Imaging device, optical component, and measurement system

Abstract

This imaging device comprises: a first optical element that separates a luminous flux from an object into a first luminous flux and a second luminous flux having optical characteristics different from those of the first luminous flux; a focusing optical system into which the first and second luminous fluxes enter at different angles and which focuses the first luminous flux to form a first image and focuses the second luminous flux to form a second image; and an image sensor that has an imaging surface. The first and second images are formed at different positions on the imaging surface. The first and second images are focused to be symmetrical on the imaging surface with respect to a plane intersecting the imaging surface.

Description

Imaging devices, optical components, and measurement systems

[0001] The present disclosure relates to imaging devices, optical components, and measurement systems.

[0002] Obtaining two images of an object with different optical properties is useful for evaluating the object. For example, obtaining two images of an object with wavelengths falling within different wavelength ranges is useful for two-color thermography, which estimates the object's temperature. The principle of two-color thermography is as follows: The intensity of thermal radiation from an object depends on the object's temperature and emissivity. Therefore, if the emissivity is unknown, measuring only the intensity of thermal radiation from the object cannot determine the object's temperature. However, if the emissivity of two different wavelength ranges can be treated as equal, the ratio of the radiation intensities in these two wavelength ranges depends on the temperature but not on the emissivity. In this case, the temperature of the object can be estimated by measuring the radiation intensities in these two wavelength ranges from the same point within the object and calculating the intensity ratio.

[0003] Acquiring two images of a subject in different wavelength ranges is also useful for fluorescence imaging. In fluorescence imaging, the fluorescence intensity is proportional to the excitation light intensity and the luminescence efficiency. Therefore, by capturing the fluorescence intensity and the excitation light intensity and calculating the intensity ratio between them, the distribution of luminescence efficiency can be visualized.

[0004] Patent Documents 1 and 2 disclose examples of imaging devices that acquire two images from a subject in different wavelength ranges.

[0005] JP 2002-214048 JP 55-124379

[0006] The present disclosure provides an imaging device that is capable of acquiring, with a simple configuration, two images that have different optical characteristics and are suitable for evaluating a subject.

[0007] An imaging device according to one aspect of the present disclosure includes: a first optical element that separates a light beam from a subject into a first light beam and a second light beam having optical properties different from those of the first light beam; an imaging optical system in which the first light beam and the second light beam are incident at different angles from each other, the imaging optical system imaging the first light beam to form a first image and the second light beam to form a second image; and an image sensor having an imaging surface. The first image and the second image are formed at different positions on the imaging surface. The first image and the second image are formed symmetrically on the imaging surface with respect to a plane intersecting the imaging surface.

[0008] A general or specific aspect of the present disclosure may be realized as a system, an apparatus, a method, an integrated circuit, a computer program, or a recording medium such as a computer-readable recording disk, or as any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a recording medium. The computer-readable recording medium may include a non-volatile recording medium such as a CD-ROM (Compact Disc-Read Only Memory). An apparatus may be composed of one or more devices. When an apparatus is composed of two or more devices, the two or more devices may be located in a single device or may be located separately in two or more separate devices. In this specification and claims, the term "apparatus" may refer not only to a single device but also to a system consisting of multiple devices.

[0009] According to the technology of the present disclosure, it is possible to realize an imaging device that can acquire, with a simple configuration, two images having different optical characteristics suitable for evaluating a subject.

[0010] FIG. 1 is a diagram schematically illustrating a configuration of an imaging device according to a first exemplary embodiment of the present disclosure. FIG. 2 is a diagram schematically illustrating a manner in which a light beam is reflected by a mirror surface. FIG. 3 is a diagram schematically illustrating a configuration of an imaging device according to a first exemplary embodiment of the present disclosure. FIG. 4 is a diagram schematically illustrating an example of a dichroic prism. FIG. 5 is a diagram schematically illustrating an example of an optical path of a light beam within a dichroic prism. FIG. 6 is a diagram schematically illustrating an example of an optical path adjustment element. FIG. 7 is a diagram schematically illustrating an example of a path of a light beam within an optical path adjustment element. FIG. 8 is a diagram schematically illustrating a path of a light beam within an optical component. FIG. 9 is a diagram for explaining general characteristics of an imaging optical system. FIG. 10 is a diagram schematically illustrating an example of a path of a light beam within an imaging device. FIG. 11 is a diagram schematically illustrating a manner in which a chief ray emitted from a certain point is imaged on an image sensor in the absence of a dichroic prism. FIG. 12A is a diagram illustrating the intermediate apparent position of a subject for the first image. FIG. 12B is a diagram illustrating the actual position of a subject for the first image. FIG. 13 is a diagram illustrating the actual position of a subject for the second image. FIG. 14 is a diagram illustrating a first light beam traveling through a first Littrow prism. FIG. 15A is a diagram illustrating a first light beam traveling through a first Littrow prism, where a light ray emitted from a certain point is focused on an image sensor. FIG. 15B is another diagram illustrating a first light beam traveling through a second Littrow prism, where a light ray emitted from a certain point is focused on an image sensor. FIG. 16 is a diagram illustrating a second light beam traveling through a second Littrow prism. FIG. 17A is a diagram illustrating a second light beam traveling through a second Littrow prism, where a light ray emitted from a certain point is focused on an image sensor. Fig. 17B is another diagram schematically showing how light rays emitted from a certain point for the second light beam are imaged on the image sensor. Fig. 18 is a diagram schematically showing the range in which the first and second light beams are imaged on the image sensor. Fig. 19 is a diagram for explaining the positional relationship between an apparent subject and an actual subject. Fig. 20 is a diagram schematically showing an example of first and second images formed on the image sensor. Fig. 21 is a diagram schematically showing how light rays emitted from a certain point for the first and second light beams are imaged on the image sensor.FIG. 22 is a diagram schematically showing the positional relationship between an apparent light blocking body, an actual light blocking body, and a dichroic prism. FIG. 23 is a diagram schematically showing a range that blocks the optical path along which the first and second light beams are imaged together on the image sensor. FIG. 24 is a diagram schematically showing an example of a filter array. FIG. 25A is a diagram schematically showing an example of connecting optical components and a lens device. FIG. 25B is a diagram schematically showing another example of connecting optical components and a lens device. FIG. 25C is a diagram schematically showing yet another example of connecting optical components and a lens device. FIG. 26 is a diagram schematically showing a specific configuration of optical components in a first modification of the image pickup device according to the first embodiment. FIG. 27 is a diagram schematically showing an optical element group in a first modification of the image pickup device according to the first embodiment. FIG. 28 is a diagram schematically showing an example of a path of a light beam within an optical element group in a first modification of the image pickup device according to the first embodiment. FIG. 29 is a diagram schematically illustrating an optical path adjusting element in a first modification of the image pickup device according to the first embodiment. FIG. 30 is a diagram schematically illustrating an example of a path of a light beam within an optical path adjusting element in the first modification of the image pickup device according to the first embodiment. FIG. 31 is a diagram schematically illustrating an example of a path of a light beam within an optical component in the first modification of the image pickup device according to the first embodiment. FIG. 32 is a diagram schematically illustrating an example of a path of a light beam within the first modification of the image pickup device according to the first embodiment. FIG. 33 is a diagram schematically illustrating a specific configuration of an optical component in a second modification of the image pickup device according to the first embodiment. FIG. 34 is a diagram schematically illustrating a dichroic prism in the second modification of the image pickup device according to the first embodiment. FIG. 35 is a diagram schematically illustrating an example of a path of a light beam within a dichroic prism in the second modification of the image pickup device according to the first embodiment. FIG. 36 is a diagram schematically illustrating an example of a path of a light beam within an optical component in the second modification of the image pickup device according to the first embodiment. FIG. 37 is a diagram schematically illustrating an example of a path of a light beam within the second modification of the image pickup device according to the first embodiment. Fig. 38 is a diagram schematically showing a specific configuration of an imaging device according to exemplary embodiment 2 of the present disclosure. Fig. 39 is a diagram schematically showing the configuration of modified example 1 of the imaging device according to embodiment 2. Fig. 40 is a diagram schematically showing the configuration of modified example 2 of the imaging device according to embodiment 2. Fig. 41 is a diagram schematically showing the configuration of modified example 3 of the imaging device according to embodiment 2.FIG. 42A is a diagram schematically illustrating an example of a measurement system including the imaging device according to Embodiment 1. FIG. 42B is a diagram schematically illustrating an example of a spectrum of thermal radiation from a subject. FIG. 43A is a diagram schematically illustrating another example of a measurement system including the imaging device according to Embodiment 1. FIG. 43B is a diagram schematically illustrating example spectra of excitation light and fluorescence. FIG. 44A is a diagram schematically illustrating yet another example of a measurement system including the imaging device according to Embodiment 1. FIG. 44B is a diagram schematically illustrating an example of an absorption spectrum of water. FIG. 44C is a diagram schematically illustrating an example of a spectrum of illumination light. FIG. 45 is a diagram schematically illustrating Example 1 of a conventional imaging device based on Patent Document 1. FIG. 46 is a diagram schematically illustrating example images of first and second wavelength ranges formed on an image sensor. FIG. 47A is a diagram schematically illustrating an example of curvature aberration. FIG. 47B is a diagram schematically illustrating another example of curvature aberration. FIG. 48 is a diagram schematically illustrating Example 2 of a conventional imaging device based on Patent Document 2.

[0011] In the present disclosure, all or part of a circuit, unit, device, component, or part, or all or part of a functional block in a block diagram, may be implemented by one or more electronic circuits, including, for example, a semiconductor device, a semiconductor integrated circuit (IC), or an LSI (large scale integration). The LSI or IC may be integrated on a single chip or may be configured by combining multiple chips. For example, functional blocks other than memory elements may be integrated on a single chip. While the terms LSI and IC are used here, the term may be changed depending on the degree of integration, and may be referred to as a system LSI, a VLSI (very large scale integration), or an ULSI (ultra large scale integration). A Field Programmable Gate Array (FPGA), which is programmed after the LSI is manufactured, or a reconfigurable logic device, which can reconfigure the connection relationships within the LSI or set up circuit sections within the LSI, can also be used for the same purpose.

[0012] Furthermore, all or part of the functions or operations of a circuit, unit, device, component, or section can be implemented by software processing. In this case, the software is recorded on one or more non-transitory recording media such as ROMs, optical disks, hard disk drives, etc., and when the software is executed by a processor, the functions specified in the software are executed by the processor and peripheral devices. A system or device may include one or more non-transitory recording media on which the software is recorded, a processor, and required hardware devices, such as interfaces.

[0013] In this disclosure, "light" refers to electromagnetic waves including not only visible light with a wavelength of about 400 nm to about 700 nm, but also ultraviolet light with a wavelength of about 10 nm to about 400 nm, and infrared light with a wavelength of about 700 nm to about 1 mm.

[0014] Exemplary embodiments of the present disclosure will be described below. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, components, component placement and connection configurations, steps, and step order shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components that are not recited in the independent claims that represent the highest concepts will be described as optional components. Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Furthermore, in each figure, substantially identical components are assigned the same reference numerals, and duplicated descriptions may be omitted or simplified.

[0015] Before describing embodiments of the present disclosure, the findings underlying the present disclosure will be explained. Below, examples 1 and 2 of conventional imaging devices that acquire two images from a subject in different wavelength ranges are described. The two images in different wavelength ranges are examples of two images having different optical properties.

[0016] [Example 1 of a conventional imaging device] FIG. 45 is a diagram schematically illustrating Example 1 of a conventional imaging device based on Patent Document 1. In an imaging device 90A shown in FIG. 45, a light beam from a subject 91 is separated into two light beams by a half mirror 92a. One light beam is reflected by a mirror 92b and passes through a band-pass filter 93a that selectively transmits light having wavelengths included in a first wavelength range. The other light beam is reflected by a mirror 92c and passes through a band-pass filter 93b that selectively transmits light having wavelengths included in a second wavelength range. The dashed arrow in FIG. 45 represents a light beam having a wavelength included in the first wavelength range, and the dotted arrow in FIG. 45 represents a light beam having a wavelength included in the second wavelength range. The half mirror 92d causes these two light beams to enter an imaging optical system 94. The imaging optical system 94 forms an image of the light beams having wavelengths included in the first and second wavelength ranges on an image sensor 95.

[0017] The half mirrors 92a and 92d are arranged at an angle of 45° with respect to the optical axis of the imaging optical system 94. In contrast, the mirrors 92b and 92c are arranged so that the images of the first and second wavelength ranges formed by imaging the two light beams are formed at different positions on the imaging surface of the image sensor 95. When the images of the first and second wavelength ranges do not overlap, the intensity of each image can be easily determined.

[0018] Fig. 46 is a diagram schematically showing an example of images in the first and second wavelength ranges formed on the image sensor 95. The subject 91 shown in Fig. 45 has a part in the shape of the letter F that emits light having wavelengths included in both the first and second wavelength ranges, against a background that emits almost no light.

[0019] The image formed by the imaging optical system 94 is rotated 180 degrees relative to the subject. However, to make the relationship with the subject easier to understand, Fig. 46 shows an image rotated so that it faces the same direction as the subject.

[0020] 46, the range of the image formed on the image sensor 95 by the imaging optical system 94 is a circular range called an image circle 95-1. The image circle 95-1 is set to be wider than an imaging range 95-2 of the image sensor 95. By forming a first image 91a of the first wavelength range and a second image 91b of the second wavelength range within the imaging range 95-2, the radiation intensities of the first and second wavelength ranges can be measured simultaneously.

[0021] 46, point 91b1 in the second image 91b corresponds to point 91a1 in the first image 91a. Similarly, point 91b2 in the second image 91b corresponds to point 91a2 in the first image 91a. Point 91b3 in the second image 91b corresponds to point 91a3 in the first image 91a. Point 91b4 in the second image 91b corresponds to point 91a4 in the first image 91a.

[0022] 46, the first image 91a and the second image 91b formed on the image sensor 95 have the same orientation. This is because the light beams having wavelengths included in the first and second wavelength ranges are both reflected the same two even number of times.

[0023] The first image 91a and the second image 91b are in a translational movement relationship, which makes it impossible to make the distance from the reference position 95-3 consistent for each point corresponding to the same position within the subject 91. The reference position 95-3 is the position where the optical axis of the imaging optical system 94 passes through the imaging range 95-2.

[0024] The characteristics of the image formed by the imaging optical system 94 vary depending on the distance from the reference position 95-3, resulting in the following problems.

[0025] The first problem is curvature aberration. The image formed by the imaging optical system 94 generally does not have a correct similarity relationship with the object 91. Figures 47A and 47B are diagrams schematically showing examples of curvature aberration. Even if a square lattice is imaged as the object 91, the imaged square lattice may be distorted like a pincushion as shown in Figure 47A or a barrel as shown in Figure 47B. The amount of this distortion depends on the relative position with respect to the reference position 95-3.

[0026] 46, the line connecting points 91a1, 91a2, and 91a3 in the first image 91a is approximately straight, but the line connecting points 91b1, 91b2, and 91b3 in the second image 91b corresponding to the same range is curved. Here, a barrel distortion is shown as an example.

[0027] When curvature aberration occurs in this way, the corresponding positional relationship between the first image 91 a and the second image 91 b is expressed using a complex function. Furthermore, the characteristics of the curvature aberration differ for each imaging optical system 94. Therefore, it is not easy to identify a first position in the first image 91 a and a second position in the second image 91 b that correspond to the same position in the subject 91, and it is not easy to calculate the intensity ratio between them.

[0028] The second problem is vignetting. Generally, an image becomes darker as it moves away from the reference position 95-3. This phenomenon is called vignetting. Due to vignetting, the ratio of the intensity at the first position in the first image 91a to the intensity at the second position in the second image 91b is equal to the ratio of the radiation intensity in the first wavelength range to the radiation intensity in the second wavelength range multiplied by the ratio of the degrees of vignetting. For example, because the distance of point 91b2 from the reference position 95-3 is longer than the distance of point 91a2 from the reference position 95-3, the ratio of the degree of vignetting of point 91b2 to that of point 91a2 is large. On the other hand, because the distance of point 91a4 from the reference position 95-3 and the distance of point 91b4 from the reference position 95-3 are equal to each other, the ratio of the degree of vignetting of point 91b4 to that of point 91a4 is approximately 1.

[0029] Determining the temperature of the subject 91 requires calculating the ratio between the intensity of thermal radiation in the first wavelength range and the intensity of thermal radiation in the second wavelength range. However, in the imaging device 90A of Patent Document 1, the intensity ratio between the first image 91a and the second image 91b formed on the image sensor 95 depends not only on the intensity ratio of the thermal radiation but also on the ratio of the degree of vignetting. Furthermore, the ratio of the degree of vignetting varies depending on the position within the first image 91a and the second image 91b. The ratio of the degree of vignetting also depends on, for example, the lens aperture.

[0030] Therefore, even if it is possible to identify positions in the first image 91a and the second image 91b that correspond to the same position in the object 91, it is not easy to determine the intensities of the thermal radiation in the first and second wavelength ranges from the imaging results. As a result, it is not easy to accurately measure the temperature of the object 91. The ratio of the intensities in the first and second wavelength ranges depends on the thermal radiation and should not depend on the imaging optical system 94. The above problem occurs in all applications that require measuring the ratio of the intensities in the first and second wavelength ranges.

[0031] [Example 2 of a conventional imaging device] Fig. 48 is a diagram schematically illustrating Example 2 of a conventional imaging device based on Patent Document 2. In an imaging device 90B shown in Fig. 48, a light beam from a subject 91 is incident on an imaging optical system 94. A dichroic prism 96 separates the light beam that has passed through the imaging optical system 94 into a light beam having a wavelength included in a first wavelength range and a light beam having a wavelength included in a second wavelength range, and causes the light beam having a wavelength included in the first wavelength range to be incident on a first image sensor 95a and the light beam having a wavelength included in the second wavelength range to be incident on a second image sensor 95b. That is, the light beam having a wavelength included in the first wavelength range is imaged on the first image sensor 95a via the dichroic prism 96 by the imaging optical system 94. The light beam having a wavelength included in the second wavelength range is imaged on the second image sensor 95b via the dichroic prism 96 by the imaging optical system 94.

[0032] In the imaging device 90B, it is necessary to arrange a first image sensor 95a and a second image sensor 95b behind the dichroic prism 96. Furthermore, it is necessary to arrange two control circuits to control these two image sensors 95a and 95b, respectively. The need for two image sensors and two control circuits increases costs. Furthermore, imaging with the imaging device 90B cannot be performed using a general camera equipped with a single image sensor 95. Therefore, it is necessary to spend time and money to develop a camera specifically for the imaging device 90B.

[0033] The imaging device 90B also has limitations on the selection of the imaging optical system 94. Generally, lens devices including the imaging optical system 94 and cameras including the image sensor 95 are designed and manufactured based on standards. Lens devices and cameras can be freely combined and used within the scope of the same standard. General standards specify the shape of the joint between the lens device and the camera. Furthermore, the distance from the joint to the image sensor 95 inside the camera, i.e., the flange back, is also specified. For example, the C-mount standard, which is widely used in industry, specifies the joint's inner diameter as 25.4 mm, thread pitch as 0.794 mm, and flange back as 17.526 mm.

[0034] Although the distance from the joint to the rearmost lens surface of the imaging optical system 94 is not normally specified in the standards, this distance is generally allowed to be zero. Therefore, the minimum value of the back focus, which is the distance from the rearmost lens surface of the imaging optical system 94 to the image sensor 95, is generally the value of the flange back.

[0035] In the imaging device 90B, dichroic prisms 96 are disposed between the imaging optical system 94 and the first image sensor 95a, and between the imaging optical system 94 and the second image sensor 95b. Therefore, the back focus of the imaging optical system 94 cannot be set equal to or smaller than the size of the dichroic prism 96. Limiting the size of the dichroic prism 96 would, for example, limit the width and angle of view of the light beam passing through it. As a result, the brightness and imaging range of the captured image would be limited. Because the back focus value of an imaging optical system 94 conforming to a general camera standard is insufficient, the dichroic prism 96 cannot be disposed when such an imaging optical system 94 is used.

[0036] General camera standards stipulate that lens devices and cameras be joined together so that the optical axis of the imaging optical system 94 is perpendicular to the imaging surface of the image sensor 95. However, in the imaging device 90B, the optical axis of the imaging optical system 94 and the imaging surface of the first image sensor 95a are in an inclined relationship. The same is true for the optical axis of the imaging optical system 94 and the imaging surface of the second image sensor 95b. Due to this arrangement, lens devices and cameras that comply with general camera standards cannot be easily combined.

[0037] Furthermore, in the imaging device 90B, a dichroic prism 96 is disposed on the side of the first image sensor 95a and the second image sensor 95b with respect to the imaging optical system 94. A convergent light beam that converges from the imaging optical system 94 toward the first image sensor 95a passes through the dichroic prism 96. The same applies to a convergent light beam that converges from the imaging optical system 94 toward the second image sensor 95b.

[0038] Because the dichroic prism 96 is made of a dielectric material, a refraction phenomenon occurs when the convergent light beam enters the dichroic prism 96 and when it exits the dichroic prism 96. When the convergent light beam passes through the dichroic prism 96, spherical aberration occurs due to this refraction phenomenon. Because the refractive index of the dielectric material is wavelength dependent, chromatic aberration also occurs.

[0039] Both spherical aberration and chromatic aberration increase as the angular spread of the convergent light beam increases. In order to suppress these aberrations, the imaging device 90B requires an increased distance between the imaging optical system 94 and the first image sensor 95a, and an increased distance between the imaging optical system 94 and the second image sensor 95b. This makes it difficult to reduce the size of the imaging device 90B.

[0040] The present inventors have found the above-mentioned problem and have conceived of imaging devices according to embodiments of the present disclosure that solve this problem. Imaging devices according to embodiments 1 and 2 will be described below. The imaging device according to embodiment 1 acquires two images from a subject in different wavelength ranges as an example of two images having different optical properties. The imaging device according to embodiment 2 acquires two images from a subject in different polarization states as another example of two images having different optical properties.

[0041] (Embodiment 1) [Imaging Device] An example configuration of an imaging device according to embodiment 1 of the present disclosure will be described below with reference to FIG. 1 . FIG. 1 is a diagram schematically illustrating the configuration of an imaging device according to exemplary embodiment 1 of the present disclosure. FIG. 1 also illustrates an object 110. The imaging device 100 illustrated in FIG. 1 acquires two images of the object 110 in different wavelength ranges. As illustrated in FIG. 1 , the imaging device 100 includes an optical component 10A including a first subcomponent 10A1 and a second subcomponent 10A2, a lens device 20A including an imaging optical system 20, and a camera 30A including an image sensor 30. However, the second subcomponent 10A2 is not necessarily an essential component of the optical component 10A. The imaging device 100 has a simple configuration in which the optical component 10A is added to the lens device 20A and the camera 30A.

[0042] The first subcomponent 10A1 includes at least one optical element. The same is true for the second subcomponent 10A2. In FIG. 1, the first subcomponent 10A1, the second subcomponent 10A2, and the imaging optical system 20 are illustrated in an abstract manner.

[0043] The first subcomponent 10A1 has a dichroic surface that separates the light beam L from the object 110 into a first light beam La having a wavelength included in a first wavelength range and a second light beam Lb having a wavelength included in a second wavelength range. The dichroic surface is disposed in a plane including the optical axis of the imaging optical system 20. The solid arrows in FIG. 1 represent the light beam L from the object 110. The dashed arrows in FIG. 1 represent the first light beam La having a wavelength included in the first wavelength range, and the dotted arrows in FIG. 1 represent the second light beam Lb having a wavelength included in the second wavelength range. The first and second wavelength ranges are different wavelength ranges.

[0044] The first subcomponent 10A1 further converts the directions of a first light beam La having a wavelength included in a first wavelength range and a second light beam Lb having a wavelength included in a second wavelength range, which become increasingly distant from each other as they move away from the dichroic surface, and outputs them toward the imaging optical system 20. By making the angle formed by the two light beams after conversion smaller than the angle formed by the two light beams before conversion, it becomes easier to cause both light beams to enter the imaging optical system 20.

[0045] The imaging optical system 20 forms an image of the first light beam La and the second light beam Lb incident thereon onto the image sensor 30, forming an image of the first wavelength range and an image of the second wavelength range at different positions on the image sensor 30. The image of the first wavelength range and the image of the second wavelength range formed on the image sensor 30 are mirror-symmetric.

[0046] However, since the dichroic surface in the first sub-component 10A1 is arranged on a plane including the optical axis of the imaging optical system 20, the direction of the light beam L incident on the dichroic surface cannot be parallel to the optical axis of the imaging optical system 20.

[0047] Therefore, a second subcomponent 10A2 may be disposed between the subject 110 and the first subcomponent 10A1. The second subcomponent 10A2 emits the light beam L from the subject 110 in a direction different from the incident direction, causing the light beam L from the subject 110 to be incident on the dichroic surface. Therefore, even if the subject 110 is located substantially on an extension of the optical axis of the imaging optical system 20, the light beam L from the subject 110 can be incident on the dichroic surface. As a result, the direction in which the subject 110 is located can be made to substantially coincide with the optical axis direction of the imaging optical system 20, making it possible to capture an image in a natural orientation.

[0048] The specific configurations of the first subcomponent 10A1 and the second subcomponent 10A2 will be described later.

[0049] In this specification, a light beam having a wavelength included in the first wavelength range is also referred to as a “first light beam,” and a light beam having a wavelength included in the second wavelength range is also referred to as a “second light beam.” An image in the first wavelength range is also referred to as a “first image,” and an image in the second wavelength range is also referred to as a “second image.”

[0050] Note that changes in the direction of travel of a light beam in an actual optical element are caused by refraction or reflection. The change in the direction of travel of a light beam due to refraction can depend, for example, on the refractive index of the optical element, the angle of incidence at which the light beam is incident on the incident surface of the optical element, and the angle of emission at which the light beam is emitted from the emission surface of the optical element. The closer the incident angle and emission angle are to perpendicular to the incident surface and emission surface, respectively, the smaller the change in the direction of travel of light due to refraction. If the incident angle and emission angle are completely perpendicular, the change in the direction of travel of light due to refraction is zero. For simplicity, in the following explanation, the change in the direction of travel of a light beam due to refraction will be ignored.

[0051] Reflection of light is caused by metals, dielectric multilayer films, or total internal reflection. Reflection caused by dielectric multilayer films other than metals and total internal reflection requires certain angular or wavelength range conditions. These conditions are well known and easily understood by those skilled in the art, so a detailed explanation is omitted. When a statement is made in this specification that reflection occurs, it is assumed that the conditions are met.

[0052] The propagation directions of the light beam L, the first light beam La, and the second light beam Lb are defined as follows. Here, the propagation direction of the light beam L is taken as an example. FIG. 2 is a diagram schematically illustrating the state in which the light beam L is reflected by a mirror surface. As shown in FIG. 2, when the light beam L is reflected by the mirror surface, the propagation direction of the light beam L changes to a direction that is a mirror image of the light beam L, with a plane perpendicular to the mirror surface as the reference direction. The direction from left to right on the paper is defined as the reference direction, and the propagation direction of the light beam L is defined by an angle from the reference direction, with a counterclockwise direction being positive. The curved arrows in FIG. 2 represent clockwise or counterclockwise. When the light beam L traveling in a direction θ is reflected by a mirror surface that forms an angle φ with the reference direction, the propagation direction of the light beam L after reflection changes to −θ + 2φ or 2π − θ + 2φ. π is the ratio of the circumference of a circle to its diameter, and angles including π are expressed in radians.

[0053] The following describes the changes in the propagation directions of the light beam L, the first light beam La, and the second light beam Lb based on the above general rule. The angles representing the propagation directions of the light beam L, the first light beam La, and the second light beam Lb can have both positive and negative values. As shown in FIG. 2 , two angles with a difference of 2nπ (n is an integer) represent the same propagation direction. All other angles basically have positive values. The angle in question can be, for example, the angle formed by two surfaces within a prism.

[0054] [Specific Configuration Example of Imaging Device] A specific configuration example of an imaging device according to the first embodiment of the present disclosure will be described below with reference to Fig. 3. Fig. 3 is a diagram schematically illustrating a specific configuration of an imaging device according to the first exemplary embodiment of the present disclosure. Fig. 3 also illustrates a subject 110. The imaging device 100 illustrated in Fig. 3 acquires two images in different wavelength ranges from the subject 110. As illustrated in Fig. 3, the imaging device 100 includes an optical component 10A, a lens device 20A, and a camera 30A.

[0055] The optical component 10A includes a dichroic prism 10, an optical path adjusting element 10-1, a light blocking body 10-2, and a housing 12 that accommodates them. However, the optical path adjusting element 10-1, the light blocking body 10-2, and the housing 12 are not essential components. The dichroic prism 10 corresponds to the first sub-component 10A1 shown in FIG. 1, and the optical path adjusting element 10-1 corresponds to the second sub-component 10A2 shown in FIG. 1.

[0056] In this specification, the dichroic prism 10 is also referred to as the "first optical element," and the optical path adjusting element 10-1 is also referred to as the "second optical element."

[0057] The lens device 20A includes an imaging optical system 20 and a lens housing 22 that houses the imaging optical system 20. The camera 30A includes an image sensor 30 and a camera housing 32 that houses the image sensor 30. However, the lens housing 22 and the camera housing 32 are not essential components. The lens device 20A and the camera 30A may be, for example, a general commercially available lens device and camera, respectively.

[0058] The imaging device 100 includes at least a dichroic prism 10, an imaging optical system 20, and an image sensor 30. The imaging device 100 may further include other components as necessary.

[0059] The imaging optical system 20 may be composed of multiple lenses, but for simplicity, it may be illustrated as a single lens or two lenses. The shapes of the lenses illustrated are also unrelated to the shapes of actual lenses. The direction and spread of the light beam may also be exaggerated.

[0060] As will be explained in detail later, in the imaging device 100, the dichroic prism 10 separates the light beam L from the subject 110 into a first light beam La and a second light beam Lb, and emits the first light beam La and the second light beam Lb symmetrically with respect to a certain plane, as shown in FIG. 3 . This plane includes the optical axis of the imaging optical system 20. The imaging optical system 20 forms an image of the first light beam La and the second light beam Lb, which are incident on the imaging optical system 20 at different angles, on the imaging surface of the image sensor 30, forming a first image and a second image at different positions on the imaging surface.

[0061] The first and second images at the imaging plane are mirror-symmetric rather than translationally displaced, which reduces the effects of aberrations. Therefore, the first and second images are suitable for evaluating the object 110 in methods such as two-color thermography and fluorescence imaging. Furthermore, the above configuration of adding the optical component 10A to the lens device 20A and camera 30A is a simple configuration.

[0062] As described above, the imaging device 100 according to the first embodiment can acquire, with a simple configuration, two images in different wavelength ranges suitable for evaluating the subject 110. Furthermore, according to the imaging device 100 according to the first embodiment, an optical path adjustment element 10-1 may be disposed between the subject 110 and the dichroic prism 10. The optical path adjustment element 10-1 changes the direction of the light beam L from the subject 110 and causes it to enter the dichroic prism 10. Therefore, the subject 110 can be imaged in a natural orientation, in which the subject 110 is positioned in the optical axis direction of the imaging optical system 20 and faces the image sensor 30.

[0063] The components of the imaging device 100 will be described in detail below.

[0064] [Components of the Imaging Device 100] <Dichroic Prism 10> Fig. 4 is a diagram schematically illustrating an example of the dichroic prism 10. As shown in Fig. 4, the dichroic prism 10 includes a first Littrow prism 10a and a second Littrow prism 10b. The first Littrow prism 10a has surfaces 10a1, 10a2, and 10a3. The second Littrow prism 10b has surfaces 10b1, 10b2, and 10b3.

[0065] The first Littrow prism 10a has a triangular prism shape and, in addition to surfaces 10a1 to 10a3, has two bottom surfaces located opposite each other. However, since these two bottom surfaces do not contribute to operation, their description will be omitted. The two bottom surfaces of the first Littrow prism 10a may be painted black to prevent reflections. The same applies to the two bottom surfaces of the second Littrow prism 10b. It is assumed that the first Littrow prism 10a and the second Littrow prism 10b have a thickness sufficient to form an image of the light beam L from the subject on the image sensor 30.

[0066] In the first Littrow prism 10a, surfaces 10a1 and 10a2 form an angle α, and surfaces 10a1 and 10a3 form an angle α'. In the second Littrow prism 10b, surfaces 10b1 and 10b2 form an angle β, and surfaces 10b1 and 10b3 form an angle β'. These angles have positive values. Because it is a Littrow prism, angles α and β are each 30°, and angles α' and β' are each 60°. However, Littrow prisms are not necessarily required, and the values ​​of the three interior angles of the prism are arbitrary. Angle α and angle β may be equal to or different from each other. Angle α' and angle β' may be equal to or different from each other. For ease of explanation, the following description will be made assuming that angles α and β are equal to each other and angles α' and β' are equal to each other.

[0067] The surfaces 10a2 and 10b2 are bonded together with an adhesive layer. The adhesive layer is transparent to light in the second wavelength range. The surfaces 10a2 and 10b2 may be parallel to each other, for example. As a result of bonding the surfaces 10a2 and 10b2 together, the first Littrow prism 10a and the second Littrow prism 10b are arranged as mirror images of each other.

[0068] One or both of surfaces 10a2 and 10b2 may be dichroic surfaces that reflect a first light beam La and transmit a second light beam Lb of the light beam L incident from a specific range of directions. The dichroic surfaces have the above-described function when the first Littrow prism 10a and the second Littrow prism 10b are bonded together. Here, the specific range of directions refers to the range of directions in which the light beam L from the subject 110 is incident. Thus, the dichroic prism 10 has at least one of the above-described dichroic surfaces.

[0069] The following description assumes that surface 10a2 is a dichroic surface, the specific range direction is close to the normal to surface 10a1, and surfaces 10a2 and 10b2 are parallel to each other. Surface 10b1 is a reflective surface that reflects second light beam Lb. Surface 10b1 may include a metal film, such as gold, silver, or aluminum, or a dielectric multilayer film. Metal films and dielectric multilayer films have high reflectivity of 60% or 80% or more for second light beam Lb. The reflection of second light beam Lb by surface 10b1 may be due to the metal film or dielectric multilayer film. Alternatively, the reflection may be due to total reflection caused by the difference between the refractive index of the material constituting second Littrow prism 10b and the external refractive index.

[0070] The paths of the light beam L, the first light beam La, and the second light beam Lb within the dichroic prism 10 will now be described. FIG. 5 is a diagram schematically illustrating an example of the paths of the light beams L, La, and Lb within the dichroic prism 10. The light beam L, the first light beam La, and the second light beam Lb shown in FIG. 5 represent only the optical paths of the chief ray. An actual dichroic prism 10 passes the light beam L, the first light beam La, and the second light beam Lb, each having a width and angular range. Even in this case, the symmetry and positional relationship required for the surfaces 10a1 to 10a3 and the surfaces 10b1 to 10b3 remain as described above. The size of the dichroic prism 10 is designed appropriately according to the widths of the light beam L, the first light beam La, and the second light beam Lb and the specifications of the imaging optical system 20.

[0071] In the first Littrow prism 10a, a light beam L incident on surface 10a1 from the outside reaches surface 10a2, as shown in FIG. 5. A component of light beam L within a first wavelength range is reflected by surface 10a2, which is a dichroic surface, to become a first light beam La. The first light beam La is reflected by surface 10a1 and emitted to the outside from surface 10a3. The reflection of first light beam La by surface 10a1 is total reflection, and the angle of incidence of first light beam La on surface 10a1 is equal to or greater than the critical angle.

[0072] The component of the light beam L within the second wavelength range passes through the dichroic surface 10a2 and the adhesive layer, and becomes a second light beam Lb in the second Littrow prism 10b. The second light beam Lb is reflected by the surface 10b1 and emitted to the outside from the surface 10b3. The reflection of the second light beam Lb by the surface 10b1 is total reflection or reflection by a metal film or a dielectric multilayer film.

[0073] In the second Littrow prism 10b, when a light beam L is incident on the surface 10b1 from the outside, a first light beam La is emitted from the surface 10b3 and a second light beam Lb is emitted from the surface 10a3, in contrast to the light beam L. However, the light shielding body 10-2 shown in FIG. 3 prevents the light beam L from being incident on the surface 10b1 from the outside. As a result, the first light beam La is emitted from the surface 10a3 of the dichroic prism 10, and the second light beam Lb is emitted from the surface 10b3 of the dichroic prism 10.

[0074] As described above, the dichroic prism 10 separates the light beam L into the first light beam La and the second light beam Lb by the surface 10a2. The dichroic prism 10 further converts the directions of the first light beam La and the second light beam Lb by the surfaces 10a1 and 10b1 and emits them.

[0075] In the dichroic prism 10, the angles α and β are equal to each other, and the angles α' and β' are equal to each other. Therefore, the optical paths of the first light beam La and the second light beam Lb are substantially symmetrical with respect to the surface 10a2.

[0076] Here, "substantially symmetrical with respect to surface 10a2" means that differences due to wavelength dependence in the refraction of light beam L, first light beam La, and second light beam Lb are negligible in the following cases: when second light beam Lb of light beam L enters second Littrow prism 10b from first Littrow prism 10a; when first light beam La is emitted from first Littrow prism 10a; and when second light beam Lb is emitted from second Littrow prism 10b. The refraction of light beam L, first light beam La, and second light beam Lb depends on the angle of incidence of light beam L on surface 10a2, the angle of incidence of first light beam La on surface 10a3, and the angle of incidence of second light beam Lb on surface 10b3. The closer these angles of incidence are to right angles, the smaller the refraction.

[0077] The first Littrow prism 10a and the second Littrow prism 10b may be designed so that the angle at which the first light beam La is emitted from the surface 10a3 and the angle at which the second light beam Lb is emitted from the surface 10b3 are close to a right angle. Alternatively, glass materials with small differences in refractive index between the first and second wavelength ranges may be selected for the first Littrow prism 10a and the second Littrow prism 10b. Selecting such glass materials reduces the possibility that the first light beam La and the second light beam Lb will not be symmetrical.

[0078] The traveling directions of the first light beam La and the second light beam Lb are as follows. With surface 10a2 as the angular reference, the traveling direction of light beam L incident on surface 10a1 is θ. In this case, the traveling direction of first light beam La reflected by surface 10a2 is −θ, and the traveling direction of first light beam La reflected by surface 10a1 is θ+2α. The traveling direction of second light beam Lb reflected by surface 10b1 is −θ−2α.

[0079] In particular, when the incident direction of the light beam L is θ=−2α, the traveling direction of the first light beam La is θ+2α=0, and the traveling direction of the second light beam Lb is −θ−2α=0. Therefore, both the first light beam La and the second light beam Lb emitted from the dichroic prism 10 are parallel to the surface 10a2.

[0080] When the incident direction of the light beam L is θ>−2α, the traveling direction of the first light beam La is θ+2α>0, and the traveling direction of the second light beam Lb is −θ−2α<0. Therefore, the first light beam La and the second light beam Lb move away from each other as they travel.

[0081] When the incident direction of the light beam L is θ<−2α, the traveling direction of the first light beam La is θ+2α<0, and the traveling direction of the second light beam Lb is −θ−2α> 0. Therefore, the first light beam La and the second light beam Lb approach each other as they travel.

[0082] As shown in Fig. 3, the first light beam La and the second light beam Lb are both incident on the imaging optical system 20. The dichroic prism 10 and the imaging optical system 20 are arranged so as to satisfy the following condition. This condition is that the first light beam La and the second light beam Lb are incident on the imaging optical system 20 so as to be substantially symmetrical with respect to a plane 24 that includes the optical axis of the imaging optical system 20, as shown in Fig. 5. This condition is satisfied when the plane 24 includes the surface 10a2.

[0083] <Imaging Optical System 20> The imaging optical system 20 is substantially symmetrical with respect to the plane 24 and has optically symmetrical properties with respect to its optical axis. The first light beam La and the second light beam Lb are incident on the imaging optical system 20 at different angles and symmetrically with respect to the plane 24. The optical axes of the first light beam La and the second light beam Lb are non-parallel to each other. The imaging optical system 20 has refractive power and forms a first image by imaging the first light beam La and a second image by imaging the second light beam Lb. Due to the symmetric incidence of the first light beam La and the second light beam Lb, the first and second images are mirror-symmetrical to each other, as will be described later.

[0084] Here, "the imaging optical system 20 is substantially symmetrical with respect to the plane 24" means that elements of the imaging optical system 20 that significantly affect the symmetry of the shapes and brightness of the first and second images are substantially symmetrical with respect to the plane 24. Fluctuations in shape, decentering, and slight positional deviations due to manufacturing tolerances may exist.

[0085] It goes without saying that the arrangement of elements that do not affect the symmetry of the first and second images is irrelevant, such as the housing 12, the lens housing 22, the camera housing 32, and the electrical circuitry. Even if symmetry is not strictly satisfied because, for example, the aperture has a polygonal shape, strict symmetry does not have to be satisfied if the effect on the symmetry of the image shape and brightness is substantially negligible.

[0086] The imaging optical system 20 is disposed so that the plane 24 includes the normal vector of the imaging surface of the image sensor 30. This includes not only the case where the optical axis of the imaging optical system 20 and the normal vector of the imaging surface of the image sensor 30 are parallel, but also the case of so-called tilt imaging, in which the optical axis of the imaging optical system 20 and the normal vector of the imaging surface of the image sensor 30 are non-parallel. Even in tilt imaging, the symmetry of the first light beam La and the second light beam Lb is maintained.

[0087] If the imaging area of ​​image sensor 30 has a symmetrical shape, plane 24 may include an axis or point of symmetry of the imaging area. For example, if the imaging area has a rectangular shape, plane 24 may be located parallel to the short side of the imaging area and pass through the midpoint of the long side.

[0088] The imaging optical system 20 may have, for example, substantially the same optical characteristics in the first and second wavelength ranges, such as lateral chromatic aberration, axial chromatic aberration, field curvature, and vignetting.

[0089] The smaller both the lateral chromatic aberration and the axial chromatic aberration are in the first and second wavelength ranges, the easier it is to identify corresponding positions in the first and second images. When the imaging optical system 20 has known lateral chromatic aberration characteristics, the corresponding positions in the first and second images may be identified based on known information.

[0090] If the curvature of field in the first and second wavelength ranges is the same, it is easier to identify corresponding positions in the first and second images. The same applies to vignetting in the first and second wavelength ranges.

[0091] <Image Sensor 30> The image sensor 30 has an imaging surface. First and second images are formed at different positions on the imaging surface. The first and second images are mirror images of each other. Even a single image sensor 30 can acquire the first and second images thus formed.

[0092] The image sensor 30 includes a plurality of photoelectric conversion elements arranged one-dimensionally or two-dimensionally. The plurality of photoelectric conversion elements form an imaging surface. The photoelectric conversion elements are sensitive to each of the first and second wavelength ranges. The photoelectric conversion elements convert the light intensity at each point in the first and second images into an electrical signal.

[0093] The sensitivity of the photoelectric conversion element in the first and second wavelength ranges may be the same or different. When capturing images of thermal radiation in the first and second wavelength ranges, one of the intensities of the thermal radiation in the first and second wavelength ranges emitted from the subject 110 is often relatively high and the other relatively low. In this case, the sensitivity in the wavelength range with the relatively high intensity may be low and the sensitivity in the wavelength range with the relatively low intensity may be high. By adjusting the sensitivity in this way, the signal intensities of the two signals become closer. As a result, the possibility of one signal being saturated due to excessive signal intensity or the other signal being buried in noise due to insufficient signal intensity can be reduced.

[0094] If the image sensor 30 includes a plurality of photoelectric conversion elements arranged one-dimensionally, the camera 30A may further include a scanning device for acquiring a two-dimensional image. The camera 30A may further include a filter array having a specific optical function, as will be described later.

[0095] The camera 30A includes a control circuit that controls the operation of the image sensor 30. The control circuit acquires the electrical signals output from each high-voltage conversion element and outputs image data.

[0096] In the imaging device 100, the lens equipment 20A and the camera 30A do not require any special elements or configurations other than those used for general imaging. Therefore, general lens equipment and cameras can be used in any combination in the imaging device 100. Because the lens equipment 20A and the camera 30A are detachable, such any combination is possible.

[0097] The lens equipment 20A and the camera 30A can be lens equipment and cameras that comply with standards such as C-mount and F-mount. In this case, it is also possible to replace one or both of the lens equipment 20A and the camera 30A within the range that complies with the standard. Such replacement is effective when changing the focal length of the lens to change the imaging range depending on the size of the subject 110, or when changing to a camera with a high frame rate for high-speed shooting.

[0098] <Optical Path Adjusting Element 10-1> The optical path adjusting element 10-1 is provided as an auxiliary element as needed. For example, as shown in FIG. 3, the optical path adjusting element 10-1 changes the direction of the light beam L from the subject 110 and causes the light beam L to enter the dichroic prism 10. The optical path adjusting element may be composed of, for example, a reflecting prism such as a Littrow prism or a half pentaprism, and a mirror.

[0099] 3, if the optical path adjusting element 10-1 is not provided, the subject 110 is disposed diagonally above the imaging optical system 20, in a direction non-parallel to the optical axis of the imaging optical system 20. When a general lens device and a camera are combined, the subject 110 is almost always positioned in the direction of the optical axis of the imaging optical system 20. Therefore, it is counterintuitive to dispose the subject 110 diagonally above the imaging optical system 20. This problem can be solved by disposing the optical path adjusting element 10-1 between the subject 110 and the dichroic prism 10.

[0100] The optical path adjustment element 10-1 reflects or totally reflects the light beam L incident on the imaging optical system 20 in a direction substantially parallel to the optical axis of the imaging optical system 20 in a direction different from the original direction. By appropriately designing the optical path adjustment element 10-1, the first light beam La and the second light beam Lb separated from the light beam L by the dichroic prism 10 are emitted from the dichroic prism 10 at an appropriate angle. As a result, the first light beam La and the second light beam Lb can be imaged by the imaging optical system 20 to form first and second images, respectively, at desired positions on the image sensor 30. The optical path adjustment element 10-1 can be designed, for example, by adjusting the angle of the surface at which reflection or total reflection occurs.

[0101] FIG. 6 is a schematic diagram illustrating an example of the light path adjusting element 10-1. In the example shown in FIG. 6, the light path adjusting element 10-1 is a Littrow prism having a triangular prism shape. The light path adjusting element 10-1 has side surfaces 10-1a1, 10-1a2, and 10-1a3. In addition to surfaces 10-1a1 to 10-1a3, the light path adjusting element 10-1 also has two bottom surfaces located on opposite sides. However, since these two bottom surfaces do not contribute to operation, their description will be omitted. Surfaces 10-1a2 and 10-1a3 form an angle γ. Since the light path adjusting element 10-1 is a Littrow prism, the angle γ is π / 6. However, the use of a Littrow prism is not necessary, and the values ​​of the three interior angles of the light path adjusting element 10-1 are arbitrary. Surface 10-1a3 may have a metal film or a dielectric multilayer film to achieve high light reflectivity.

[0102] 7 is a diagram schematically showing an example of the path of the light beam L in the optical path adjusting element 10-1. As shown in Fig. 7, the surface 10-1a3 is inclined at an angle η with respect to the surface 10a2 shown in Fig. 5.

[0103] Light beam L traveling in a direction φ is incident on surface 10-1a1 and then totally reflected by surface 10-1a2. Because surface 10-1a2 is tilted by an angle η+γ with respect to surface 10a2, the traveling direction of light beam L totally reflected by surface 10-1a2 is −φ+2(η+γ). Light beam L totally reflected by surface 10-1a2 is then totally reflected by surface 10-1a3. The traveling direction of light beam L totally reflected by surface 10-1a3 is −(−φ+2(η+γ))+2η=φ-2γ. In other words, the traveling direction of light beam L totally reflected by surface 10-1a3 is rotated by an angle −2γ from the traveling direction of light beam L incident on surface 10-1a1 and is independent of angle η. This is because the effect of angle η is canceled out by reflections from surfaces 10-1a2 and 10-1a3.

[0104] This phenomenon occurs in all prisms in which the light beam L, the first light beam La, and the second light beam Lb are reflected twice on the inner surface. Therefore, in the following, when the light beam L, the first light beam La, and the second light beam Lb are reflected twice on the inner surface of a prism, the arrangement angle of the prism will not be specifically mentioned.

[0105] In the imaging device 100, instead of or in addition to the optical path adjusting element 10-1, at least one of the following may be arranged: an optical filter, an optical system, and a light blocking body. The optical filter blocks or attenuates light beams in wavelength ranges other than the first and second wavelength ranges. The optical system corrects spherical aberration caused by a prism. The light blocking body limits the imaging range of the subject 110.

[0106] <Light Blocking Body 10-2> The light blocking body 10-2 is provided as an auxiliary element as needed. The light blocking body 10-2 blocks unintended light beams from entering the dichroic prism 10. As a result, stray light can be reduced. As shown in FIG. 3, the light blocking body 10-2 is provided so that the light beam L from the outside is incident on a specific surface of the first Littrow prism 10a shown in FIG. 5 of the dichroic prism 10, but is prevented from entering any other surface. This specific surface is surface 10a1 shown in FIG. 5. The light blocking body 10-2 blocks the light beam L from the outside from entering surface 10b1 of the second Littrow prism 10b shown in FIG. 5 of the dichroic prism 10. The light blocking body 10-2 further blocks the light beam L from entering the two bottom surfaces of the first Littrow prism 10a and the two bottom surfaces of the second Littrow prism 10b.

[0107] 3, the light blocking body 10-2 may be a light blocking object disposed at a distance from the dichroic prism 10. Alternatively, the light blocking body 10-2 may be a light blocking layer formed on one of the surfaces of the dichroic prism 10 onto which the light beam is not intended to be incident. The metal film or dielectric multilayer film on the surface 10b1 that reflects the second light beam Lb may also be configured to function as the light blocking body 10-2.

[0108] [Paths of the Light Beam L, First Light Beam La, and Second Light Beam Lb Within the Optical Component 10A] Figure 8 is a diagram schematically showing the paths of the light beam L, first light beam La, and second light beam Lb within the optical component 10A. Note that the light blocking body 10-2 and the housing 12 shown in Figure 3 are omitted from Figure 8. The light beam L incident on the optical path adjustment element 10-1 in the direction φ is reflected on the inner surface and finally exits from the optical path adjustment element 10-1 in the direction φ-2γ.

[0109] Light beam L enters dichroic prism 10 through surface 10a1 and is separated by surface 10a2 into a first light beam La and a second light beam Lb. Ultimately, first light beam La is emitted from dichroic prism 10 in a direction φ-2γ+2α, and second light beam Lb is emitted from dichroic prism 10 in a direction -φ+2γ-2α. In other words, optical component 10A emits incident light beam L as first light beam La and second light beam Lb that are mirror-symmetric with respect to surface 10a2.

[0110] In particular, when φ=2γ−2α is satisfied, the directions of travel of the first light beam La and the second light beam Lb emitted from the dichroic prism 10 are both zero. If the angle γ is made to approximately coincide with the angle α, the direction φ is also approximately zero. Therefore, when the direction of travel of the light beam L incident on the optical path adjustment element 10-1 is approximately parallel to the optical axis of the imaging optical system 20, the directions of travel of the first light beam La and the second light beam Lb emitted from the dichroic prism 10 are also approximately parallel to the optical axis of the imaging optical system 20.

[0111] In this specification, the phrase "the traveling directions of the light beam L, the first light beam La, and the second light beam Lb are approximately parallel to the optical axis direction of the imaging optical system 20" means not only when the traveling directions of the light beam L, the first light beam La, and the second light beam Lb are strictly parallel to the optical axis direction of the imaging optical system 20, but also when the angle between the traveling directions of the light beam L, the first light beam La, and the second light beam Lb and the optical axis direction of the imaging optical system 20 is π / 36 or less.

[0112] 9 is a diagram for explaining the general characteristics of the imaging optical system 20. The imaging optical system 20 has a front principal point 26a and a rear principal point 26b on its optical axis.

[0113] Of the light rays that are incident in a direction -θ with respect to the optical axis of the imaging optical system 20, those that pass through the front principal point 26a become light rays that are emitted from the rear principal point 26b in a direction -θ. Similarly, of the light rays that are incident in a direction θ with respect to the optical axis of the imaging optical system, those that pass through the front principal point 26a become light rays that are emitted from the rear principal point 26b in a direction θ. Here, the light rays that pass through the front principal point 26a are called chief rays.

[0114] If the distance from rear principal point 26b to image sensor 30 is D, then object 110, whose image is formed at a position D tan θ on image sensor 30 using plane 24 as the reference, is located in the direction θ+π using front principal point 26a as the reference. Similarly, object 110, whose image is formed at a position −D tan θ on image sensor 30 using plane 24 as the reference, is located in the direction −θ−π using front principal point 26a as the reference. The relationship between the direction of object 110 and the image position on image sensor 30 can be determined from the above chief ray.

[0115] 10 is a diagram schematically illustrating an example of the paths of the light beam L, the first light beam La, and the second light beam Lb within the image capturing device 100. However, in FIG. 10, the light blocking body 10-2, the housing 12, the lens housing 22, and the camera housing 32 shown in FIG. 3 are omitted. From the relationship between the incident direction of the light beam L and the emission directions of the first light beam La and the second light beam Lb, the relationship between the direction in which the subject 110 is located and the imaging position can be determined.

[0116] 10 , when the light beam L is incident on the optical path adjustment element 10-1 in a direction φ=−θ+2γ−2α, the first light beam La is incident on the imaging optical system 20 in a direction −θ and passes through the front principal point 26a, and the second light beam Lb is incident on the imaging optical system 20 in a direction θ and passes through the front principal point 26a. In this case, the first light beam La forms an image at a position of −D tan θ on the image sensor 30, and the second light beam Lb forms an image at a position of D tan θ on the image sensor 30. In other words, the first and second images on the image sensor 30 are mirror-symmetric with respect to a plane including the surface 10a2.

[0117] The first light beam La is emitted from the surface 10a3 of the first Littrow prism 10a. Therefore, when the traveling direction -θ of the first light beam La is negative, the first light beam La may include a chief ray passing through the front principal point 26a. In contrast, when the traveling direction -θ of the first light beam La is positive, the first light beam La does not include such a chief ray. With respect to the plane 24 as the reference, the first image is formed on the image sensor 30 on the side of the second Littrow prism 10b. Although the first image may be formed on the image sensor 30 on the side of the first Littrow prism 10a, it is generally darkened due to the effects of vignetting.

[0118] The second light beam Lb is emitted from the surface 10b3 of the second Littrow prism 10b. Therefore, if the traveling direction θ of the second light beam Lb is positive, the second light beam Lb may include a chief ray passing through the front principal point 26a. If the traveling direction θ of the second light beam Lb is negative, the second light beam Lb does not include such a chief ray. With respect to the plane 24 as the reference, the second image is formed on the image sensor 30 on the side of the first Littrow prism 10a. Although the second image may be formed on the image sensor 30 on the side of the second Littrow prism 10b, it is generally dark due to the effects of vignetting.

[0119] Therefore, the areas on the image sensor 30 where the first and second images are primarily formed are different.

[0120] When the direction θ is zero, it is the object 110 located in the direction φ=2γ−2α that is formed as the first and second images at the positions where the optical axis of the imaging optical system 20 intersects with the image sensor 30. In other words, the object 110 located in the direction φ=2γ−2α is imaged at the center of the image sensor 30.

[0121] Here, when α = γ, the direction in which the subject 110 is located is φ = 0. Therefore, the light beam L from the subject 110, which is located in the optical axis direction of the imaging optical system 20, is formed as first and second images at positions where the optical axis of the imaging optical system 20 intersects with the image sensor 30. The centers of the areas in which the first and second images are formed are located in the direction of θ = 0.

[0122] In contrast, when α≠γ, the direction in which the subject 110 is located is φ≠0. Conversely, the light beam L incident in the direction φ=0 becomes a first light beam La emitted in the direction -θ=-2γ+2α, and a second light beam Lb emitted in the direction θ=2γ-2α. With this configuration, when the subject 110 is located on the optical axis of the imaging optical system 20, the first light beam La and the second light beam Lb can be imaged at different positions on the image sensor 30.

[0123] For example, the center of the range in which the first light beam La forms an image on the image sensor 30 is located at -Dtan(2γ-2α), and the center of the range in which the second light beam Lb forms an image on the image sensor 30 is located at Dtan(2γ-2α). By selecting α and γ so that these values ​​are achieved, the center of the subject 110 corresponding to the center of each of the first and second images can be positioned in the optical axis direction of the imaging optical system 20. As a result, it becomes possible to acquire the first and second images by orienting the imaging optical system 20 in a natural direction.

[0124] 10, the configuration in which the dichroic prism 10 and the optical path adjusting element 10-1 are combined is compact because the distance between them can be narrowed. Furthermore, the shape of the prism used in this configuration is simple.

[0125] [Principle of Acquiring First and Second Images] Next, the principle of acquiring the first and second images by the imaging device 100 according to the first embodiment will be described. The following describes the positional relationship in which the images of the various parts of the subject 110 shown in FIG. 3 are formed on the image sensor 30. For simplicity of explanation, the optical path adjustment element 10-1 is not taken into consideration here.

[0126] 11 is a diagram showing a schematic diagram of how a chief ray emitted from a certain point forms an image on the image sensor 30 in the absence of the dichroic prism 10. As shown in FIG. 11, in the absence of the dichroic prism 10, if a plane conjugate with the image sensor 30 by the imaging optical system 20 is defined as an object plane 112, an image on the object plane 112 is formed on the image sensor 30.

[0127] The imaging range of the image sensor 30 as viewed from the imaging optical system 20 side is determined based on the focal length of the imaging optical system 20, the range in which vignetting occurs, and the size of the image sensor 30. In the following, it is assumed that the imaging range has a rectangular shape and is symmetrical with respect to the plane 24.

[0128] When no mirror is placed in the optical path, the position on the object plane 112 that is conjugate to point a on the image sensor 30 is defined as point A, the position on the object plane 112 that is conjugate to point b on the image sensor 30 is defined as point B, and the position on the object plane 112 that is conjugate to point c on the image sensor 30 is defined as point C. Point b is located on the optical axis of the imaging optical system 20, and points a and c are located at the ends of the imaging range.

[0129] That is, an image of the subject 110 within the range of the line segment A-C on the subject plane 112 is acquired by the image sensor 30. The lengths of the line segments a-b and bc are equal, and the lengths of the line segments A-B and BC are equal.

[0130] By disposing a mirror at the following position, the object plane 112 moves to the destination of the light reflected by the mirror. This position is on the opposite side of the image sensor 30 with respect to the imaging optical system 20. This position is also closer to the imaging optical system 20 than the object plane 112. This position is also on the optical path that allows the image sensor 30 to capture an image.

[0131] The object 110 that is actually imaged is located on the object plane after this movement, but if the mirror is ignored, the object 110 appears to be located on the object plane 112. In this specification, this is referred to as the apparent object position.

[0132] The following describes an example in which the subject 110 has a planar shape, is located on a single plane perpendicular to the surface 10a2 of the dichroic prism 10, and is perpendicular to the optical axis of the imaging optical system 20. For subjects 110 that are not located on this single plane, imaging results can be calculated using elementary geometry, so a description thereof will be omitted.

[0133] <First Image> Regarding the first image, a description will be given of the positional relationship between the apparent subject and the actual subject 110. As will be described later, not all of the range of the actual subject 110 is imaged within the imaging range on the image sensor 30.

[0134] As shown in FIG. 5, when light beam L from subject 110 is incident on surface 10a1 of first Littrow prism 10a from the outside, surfaces 10a1 and 10a2 function as mirror surfaces that reflect a first light beam La separated from light beam L. On the other hand, when light beam L from subject 110 is incident on surface 10b1 of second Littrow prism 10b from the outside, surfaces 10b1 and 10b2 function as mirror surfaces that reflect the first light beam La separated from light beam L. However, because the light beam incident on surface 10b1 from the outside is blocked by light shielding body 10-2 shown in FIG. 3, the latter first light beam La does not form an image on image sensor 30. Therefore, with regard to first light beam La, only the first light beam La separated from light beam L incident on surface 10a1 is considered.

[0135] After being reflected by surface 10a2, first light beam La is further reflected by surface 10a1 and enters imaging optical system 20. By tracing the optical path of first light beam La in reverse, the actual position of subject 110 can be determined from the apparent position of the subject. That is, after determining the intermediate apparent position of the subject due to reflection by surface 10a1, the actual position of subject 110 due to reflection by surface 10a2 can be determined.

[0136] FIG. 12A is a diagram illustrating the intermediate apparent position of the subject due to reflection at surface 10a1 for the first image. As shown in FIG. 12A, the plane including surface 10a1 is designated as plane 10a4. The intersection of plane 10a4 with plane 24 and the plane including points A to C and the optical axis of the imaging optical system 20 is designated as point O. ∠BOA is designated as γ. γ has a negative value. Since the lengths of line segments B-A and B-C are equal, ∠BOC is designated as -γ. However, it is assumed that the angle increases counterclockwise on the paper, with the optical axis of the imaging optical system 20 as the zero reference.

[0137] When the optical path is viewed from the image sensor 30 side, the first reflective surface encountered is surface 10a1. When at least a portion of the light beams converging on points a, b, and c shown in Figure 11 are reflected by surface 10a1, the conjugate positions move to positions symmetrical with respect to surface 10a1. As a result, as shown in Figure 12A, points A1, B1, and C1 become conjugate with points a, b, and c, respectively.

[0138] ∠BOA1 is 2α-γ, ∠BOB1 is 2α, and ∠BOC1 is 2α+γ. The lengths of line segments AO and A1O are equal to each other. Similarly, the lengths of line segments BO and B1O are equal to each other. The lengths of line segments CO and C1O are equal to each other. The positions of points A1, B1, and C1 are the positions of the intermediate apparent object for the first luminous flux La.

[0139] 12B is a diagram illustrating the actual position of the object due to reflection from surface 10a2 in the first image. As shown in FIG. 12B, points A1, B1, and C1 move to points A2, B2, and C2, respectively, due to reflection from surface 10a2. Points A2, B2, and C2 are symmetrical to points A1, B1, and C1, respectively, with respect to plane 24. Object 110 located at points A2, B2, and C2 appears to be located at apparent points A1, B1, and C1. Points A2, B2, and C2 exist on actual object plane 114.

[0140] The lengths of line segments A1O and A2O are equal to each other. Similarly, the lengths of line segments B1O and B2O are equal to each other. The lengths of line segments C1O and C2O are equal to each other. Therefore, the lengths of line segments AO and A2O are equal to each other. Similarly, the lengths of line segments BO and B2O are equal to each other. The lengths of line segments CO and C2O are equal to each other.

[0141] ∠BOA2 is γ-2α, ∠BOB2 is -2α, and ∠BOC2 is -γ-2α. In other words, the positions of points A2, B2, and C2 are obtained by rotating points A, B, and C by -2α around point O, respectively.

[0142] In summary, with respect to the first light beam La, the object 110 that is actually located at points A2, B2, and C2 appears to be located at apparent points A, B, and C.

[0143] The object 110 reflected by the reflecting surface becomes a so-called mirror-inverted image with each reflection. Therefore, an image that has been reflected an odd number of times becomes a mirror-inverted image compared to an image that has not been reflected. An image that has been reflected an even number of times becomes a non-mirror-inverted image compared to an image that has not been reflected.

[0144] Two mirror image inversions are mathematically equivalent to one rotation. The first light beam La is reflected twice by the surfaces 10a1 and 10a2 of the dichroic prism 10. Therefore, the first image formed on the image sensor 30 is an image that is not mirror-inverted with respect to the image that has not undergone reflection. The position of the subject 110 that is actually imaged is at a position rotated by −2α from the apparent position of the subject around point O as the rotation axis.

[0145] <Second Image> The positional relationship between the apparent subject and the actual subject 110 for the second image will be described. As with the first light beam La, the light beam incident from the surface 10b1 is blocked. Therefore, for the second light beam Lb, only the optical path of the second light beam Lb separated from the light beam L incident on the surface 10a1 of the first Littrow prism 10a is taken into consideration.

[0146] FIG. 13 is a diagram illustrating the position of the actual subject 110 in the second image due to reflection from surface 10b1. When viewing the optical path from the image sensor 30 side, surface 10b1 is the only reflective surface present. As shown in FIG. 13, a plane including surface 10b1 is designated plane 10b4. Points A3, B3, and C3 are symmetrical to points A, B, and C, respectively, with plane 10b4 as the reference. The subject 110 located at points A3, B3, and C3 appears to be located at apparent points A, B, and C. Points A3, B3, and C3 exist on the actual subject plane 116.

[0147] ∠BOA3 is -γ-2β, ∠BOB3 is -2β, and ∠BOC3 is γ-2β. When α = β, ∠BOA3 is -γ-2α, ∠BOB3 is -2α, and ∠BOC3 is γ-2α. The lengths of line segments AO and A3O are equal. Similarly, the lengths of line segments BO and B3O are equal. The lengths of line segments CO and C3O are equal.

[0148] If the refractive power of imaging optical system 20 is equal in the first and second wavelength ranges, object plane 116 shown in Figure 13 is the same as object plane 114 shown in Figure 12B. That is, point A3 is the same as point C2, point B3 is the same as point B2, and point C3 is the same as point A2.

[0149] The apparent objects in the first and second wavelength ranges as seen from the actual object 110 are mirror images of each other. That is, the first and second images formed on the image sensor 30 are mirror images of each other.

[0150] This is because the first light beam La is reflected twice an even number of times by the surfaces 10a1 and 10a2, while the second light beam Lb is reflected once an odd number of times by the surface 10b1. In other words, when one of the two light beams is reflected an even number of times and the other an odd number of times, the two images are mirror images of each other.

[0151] In the above example, the optical path of the first light beam La and the optical path of the second light beam Lb have been described separately. In reality, the first light beam La and the second light beam Lb form images simultaneously. As a result, the first and second images are acquired simultaneously by the image sensor 30. This is because the optical path lengths of the first light beam La and the second light beam Lb are equal to each other.

[0152] [Areas Imaged by First Light Beam La and Second Light Beam Lb] The correspondence relationship between the subject 110 and the first and second images on the image sensor 30 is as described above. In reality, the first and second images formed on the image sensor 30 differ depending on, for example, the relative positional relationships between the dichroic prism 10, the imaging optical system 20, the image sensor 30, the optical path adjustment element 10-1, and the light blocking body 10-2. The first and second images also differ depending on, for example, the sizes, focal lengths, and aperture settings of these components.

[0153] A light ray emitted in a certain direction from a certain point within the subject 110 passes through the optical path adjustment element 10-1, the dichroic prism 10, and the imaging optical system 20, and reaches the imaging range on the image sensor 30. As a result, an image of the certain point within the subject 110 is acquired by the image sensor 30. If a light ray emitted in any direction from a certain part within the subject does not reach the imaging range on the image sensor 30, an image of that part within the subject 110 is not formed.

[0154] The following describes the range of the subject 110 that is actually imaged on the image sensor 30. The imaging device 100 is configured so that only light beams that have passed through both the dichroic prism 10 and the imaging optical system 20 reach the imaging range on the image sensor 30. Such a configuration is possible by appropriately adjusting the size of the dichroic prism 10, the positional relationship between the dichroic prism 10 and the imaging optical system 20, the focal length of the imaging optical system 20, and the size and position of the light blocking body 10-2. The following description assumes such a configuration. In other words, no light beams enter the imaging optical system 20 without passing through the dichroic prism 10.

[0155] First, we will explain the range over which the first light beam La actually forms an image on the image sensor 30. FIG. 14 is a schematic diagram showing the first light beam La traveling through the first Littrow prism 10a. The light beam L from the subject 110 includes the first light beam La as a part of it. As shown in FIG. 14, the first light beam La passes through surface 10a1 of the first Littrow prism 10a from the outside, is reflected by surfaces 10a2 and 10a1 in that order, and passes through surface 10a3. Therefore, the light beam that does not pass through or is reflected by surfaces 10a1 to 10a3 does not form an image on the image sensor 30.

[0156] If we trace the optical path from the imaging optical system 20 side, the first light beam La passes through surface 10a3, is reflected by surfaces 10a1 and 10a2 in that order, and passes through surface 10a1. Due to the reflection from surface 10a1, the first Littrow prism 10a appears to be a prism 11a. The prism 11a is symmetrical to the first Littrow prism 10a with respect to a plane including surface 10a1. The surface 10a2 appears to be the corresponding surface 11a2 of the prism 11a.

[0157] Furthermore, due to reflection at surface 10a2, prism 11a appears to be prism 13a. Prism 13a is symmetrical to prism 11a with respect to a plane including surface 11a2. Surface 10a1, which serves as a passing plane, appears to be the corresponding surface 13a1 of prism 13a.

[0158] Therefore, the first light beam La corresponds to the apparent light beam Lc that passes from the apparent subject through the thick plate that combines the actual first Littrow prism 10a and the two apparent prisms 11a and 13a. The dashed-dotted arrow in Figure 14 represents the light beam Lc. If the actual first light beam La that passes through the first Littrow prism 10a exists, the apparent light beam Lc can be considered. Conversely, if the apparent light beam Lc cannot be considered, the actual first light beam La does not exist.

[0159] The existence of a light beam passing through the surface 13a1 of the apparent prism 13a and the surface 10a3 of the first Littrow prism 10a is a necessary condition for the first light beam La to be imaged.

[0160] Figures 15A and 15B are schematic diagrams showing how light rays emitted from a certain point are imaged on the image sensor 30 for the first light beam La when apparent prisms 11a and 13a are present in addition to the dichroic prism 10.

[0161] 15A, line segment AB is located on the side of surface 13a1 and surface 10a3 through which first luminous flux La must pass, relative to plane 24. Therefore, a point on line segment AB on the apparent subject can be imaged within the imaging range of image sensor 30 by appropriately designing the size and position of first Littrow prism 10a.

[0162] In contrast, line segment BC is on the opposite side of plane 24 from surfaces 13a1 and 10a3. Therefore, the chief ray emitted from a point on line segment BC does not pass through surfaces 13a1 and 10a3, regardless of the size and position of first Littrow prism 10a. However, even if a light ray is emitted from a point on line segment BC, a light ray that travels an optical path other than that of the chief ray may be imaged within the imaging range of image sensor 30.

[0163] 15B , point F is the apparent position that is the boundary of the range where light rays that have passed through surfaces 13a1 and 10a3 are imaged in the imaging range on image sensor 30 by imaging optical system 20. Point f is the position where light rays that appear to be emitted from point F are imaged on image sensor 30.

[0164] A point on the line segment B-F on the apparent subject is imaged by the imaging optical system 20 onto a line segment b-f on the imaging range on the image sensor 30. A point on the line segment FC on the apparent subject is not imaged in the imaging range on the image sensor 30 because the chief ray emitted from that point does not pass through the imaging optical system 20.

[0165] If the dichroic prism 10 is not provided, an image of the range of the line segment A-C on the apparent subject is formed in the imaging range of the image sensor 30. In contrast, if the dichroic prism 10 is actually provided, for the first light beam La, only the ranges of the line segments A-B and B-F on the apparent subject are formed in the imaging range of the image sensor 30. An image of the range of the line segment F-C on the apparent subject is not formed because light rays do not reach the image sensor 30.

[0166] Next, the range in which the second light beam Lb actually forms an image on the image sensor 30 will be described. FIG. 16 is a schematic diagram showing the second light beam Lb traveling through the second Littrow prism 10b. The light beam L from the subject 110 includes the second light beam Lb as a part of itself. As shown in FIG. 16, the second light beam Lb passes from the outside through surfaces 10a1, 10a2, and 10b2 of the first Littrow prism 10a, is reflected by surface 10b1 of the second Littrow prism 10b, and passes through surface 10b3. Therefore, the light beam that does not pass through or is reflected by surfaces 10a1, 10a2, and surfaces 10b1 to 10b3 does not form an image on the image sensor 30.

[0167] If we follow the optical path from the imaging optical system 20 side, the second light beam Lb passes through the surface 10b3, is reflected by the surface 10b1, and passes through the surfaces 10b2, 10a2, and 10a1 in this order.

[0168] Due to reflection at surface 10b1, second Littrow prism 10b appears to be prism 11b, and first Littrow prism 10a appears to be prism 15a. Prism 11b is symmetrical to second Littrow prism 10b with respect to a plane including surface 10b1. Prism 15a is symmetrical to first Littrow prism 10a with respect to a plane including surface 10b1. Surface 10a1, as a passing plane, appears to be the corresponding surface 15a1 of prism 15a.

[0169] Therefore, the second light beam Lb corresponds to the apparent light beam Ld that passes from the apparent subject through the thick plate formed by the actual second Littrow prism 10b and the two apparent prisms 11b and 15a. The two-dot chain arrow in Figure 16 represents the apparent light beam Ld. If the actual second light beam Lb that passes through the second Littrow prism 10b exists, the apparent light beam Ld can be considered. Conversely, if the apparent light beam Ld cannot be considered, the actual second light beam Lb does not exist.

[0170] The existence of a light beam passing through the surface 15a1 of the apparent prism 15a and the surface 10b3 of the second Littrow prism 10b is a necessary condition for the second light beam Lb to form an image.

[0171] Figures 17A and 17B are schematic diagrams showing how light rays emitted from a certain point are imaged on the image sensor 30 for the second light beam Lb when apparent prisms 11b and 15a are present in addition to the dichroic prism 10.

[0172] 17A, line segment BC is located on the side of surface 15a1 and surface 10b3 through which second light beam Lb must pass, with plane 24 as the reference. Therefore, a point on line segment BC on the apparent subject can be imaged within the imaging range of image sensor 30 by appropriately designing the size and position of first Littrow prism 10a and second Littrow prism 10b.

[0173] In contrast, line segment AB is on the opposite side of plane 24 from surfaces 15a1 and 10b3. Therefore, the chief ray emitted from a point on line segment AB does not pass through surfaces 15a1 and 10b3, regardless of the size and position of first Littrow prism 10a and second Littrow prism 10b. However, even if a light ray is emitted from a point on line segment AB, a light ray that travels an optical path other than that of the chief ray may be imaged within the imaging range of image sensor 30.

[0174] 17B, ​​point G is the apparent position that is the boundary of the range where light rays that have passed through surfaces 15a1 and 10b3 are imaged in the imaging range on image sensor 30 by imaging optical system 20. Point g is the position where light rays that appear to be emitted from point G are imaged on image sensor 30.

[0175] A point on the line segment GB on the apparent subject is imaged by the imaging optical system 20 onto the line segment gb on the imaging range on the image sensor 30. A point on the line segment A-G on the apparent subject is not imaged in the imaging range on the image sensor 30 because the chief ray emitted from that point does not pass through the imaging optical system 20.

[0176] If the dichroic prism 10 is not provided, an image of the range of the line segment A-C on the subject is formed in the imaging range of the image sensor 30. In contrast, if the dichroic prism 10 is actually provided, for the second light beam Lb, only the ranges of the line segment B-C and the line segment GB on the apparent subject are formed in the imaging range of the image sensor 30. No image is formed in the range of the line segment A-G on the apparent subject because light rays do not reach the image sensor 30.

[0177] 18 is a diagram schematically showing the ranges in which the first light beam La and the second light beam Lb are imaged on the image sensor 30. As shown in FIG. 18, a first image is formed in a range 30a of the line segment a-f on the image sensor 30, and a second image is formed in a range 30b of the line segment g-c. In this case, only the first image is formed in a range 32a of the line segment a-g, only the second image is formed in a range 32b of the line segment f-c, and the first and second images are superimposed and formed in a range 32c of the line segment g-f.

[0178] [Positional Relationship Between Apparent Subject and Actual Subject] Figure 19 is a diagram for explaining the positional relationship between the apparent subject and the actual subject. As shown in Figure 19, for the first image, points A, B, and F of the apparent subject correspond to points A2, B2, and F2 of the actual subject, respectively. Similarly, for the second image, points B, C, and G of the apparent subject correspond to points B3, C3, and G3 of the actual subject, respectively. As described above, points A2 and C3 are the same, and points B2 and B3 are the same. Similarly, points F2 and G3 are the same.

[0179] [Positional Relationship Between First and Second Images] Fig. 20 is a diagram schematically showing an example of the first and second images formed on the image sensor 30. The subject 110 shown in Fig. 3 is as described with reference to Fig. 45.

[0180] An imaging range 36 of the image sensor 30 exists within an image circle 34 formed on the image sensor 30 by the imaging optical system 20. A first image 110a and a second image 110b are formed within the imaging range 36. The first image 110a and the second image 110b are in a mirror-symmetric relationship with respect to the plane 24. The first image 110a and the second image 110b are formed within ranges 32a and 32b shown in FIG. 18 so as not to overlap each other. The range 32a corresponds to the range of the line segment A2-F2 shown in FIG. 19, and the range 32b corresponds to the range of the line segment G3-C3 shown in FIG. 19.

[0181] The first light beam La and the second light beam Lb, which are emitted from a point within the subject 110 and form an image on the image sensor 30, travel along the same optical path until they reach the surface 10a2. After reaching the surface 10a2, the first light beam La and the second light beam Lb travel along different optical paths that are symmetrical with respect to the plane 24. These different optical paths pass through the dichroic prism 10 and the imaging optical system 20.

[0182] The first light beam La and the second light beam Lb traveling along such symmetrical optical paths are subject to the same degree of vignetting by the dichroic prism 10 and the imaging optical system 20. The dichroic prism 10 and the imaging optical system 20 are also subject to the same degree of vignetting. Therefore, in the first image 110a and the second image 110b, the light rays having wavelengths included in the first and second wavelength ranges that are emitted from the same point within the subject 110 experience the same rate of vignetting and vignetting. By calculating these intensity ratios, the effects of vignetting and vignetting can be ignored.

[0183] Both the first image 110a and the second image 110b may be distorted by curvature aberration. However, the curvature aberration occurs symmetrically with respect to the plane 24. Corresponding positions in the first image 110a and the second image 110b are symmetric with respect to the plane 24, regardless of the form of the curvature aberration. Therefore, it is extremely easy to determine the corresponding positions.

[0184] As shown in FIG. 20 , point 110b1 in the second image 110b corresponds to point 110a1 in the first image 110a. Similarly, point 110b2 in the second image 110b corresponds to point 110a2 in the first image 110a. Point 110b3 in the second image 110b corresponds to point 110a3 in the first image 110a. Point 110b4 in the second image 110b corresponds to point 110a4 in the first image 110a. Points 110b1 to 110b4 in the second image 110b are symmetrical to points 110a1 to 110a4 in the first image 110a, respectively, with respect to plane 24. Points corresponding to the same position in the object 110 have the same distance from the reference position 38. The reference position 38 is the position where the optical axis of the imaging optical system 20 passes through the imaging range 36.

[0185] As described above, the first image 110a and the second image 110b are in a mirror-symmetric relationship with respect to the plane 24. The ratio of the radiation intensities from corresponding points in the first image 110a and the second image 110b is calculated, and the sensitivity of the image sensor 30 is corrected as necessary. As a result, the ratio of the radiation intensities in the first and second wavelength ranges from corresponding points in the subject 110 can be accurately obtained.

[0186] [Measures for Reducing the Area Where the First and Second Images Overlap] The area of ​​line segment F-G shown in Figure 19 corresponds to the area where the first image 110a and the second image 110b overlap on the image sensor 30. It may be possible to acquire the first image 110a and the second image 110b separately by performing a mathematical separation operation. However, it is more practical to be able to acquire the first image 110a and the second image 110b separately without such an operation.

[0187] A first method for narrowing the overlapping range of the first image 110a and the second image 110b will now be described. The first method is to use a light blocking body. FIG. 21 is a schematic diagram illustrating how light rays emitted from a certain point are imaged on the image sensor 30 when the dichroic prism 10 and the apparent prisms 11a, 13a, 15a, and 11b are present in addition to the dichroic prism 10, for the first light beam La and the second light beam Lb. As shown in FIG. 21 , point F' is the apparent position where the light rays passing through point Z, surfaces 13a1, and 10a3 are imaged in the imaging range on the image sensor 30 by the imaging optical system 20. Similarly, point G' is the apparent position where the light rays passing through point Z, surfaces 15a1, and 10b3 are imaged in the imaging range on the image sensor 30 by the imaging optical system 20. Point Z is located on the line segment O-B.

[0188] As shown in Fig. 21 , an apparent light blocking body represented by a thick line is located between point O and point Z. Light rays that cross this light blocking body are not imaged on the image sensor 30. Light rays that are emitted from line segment A-B shown in Fig. 19 and that are imaged on the image sensor 30 do not cross the apparent light blocking body. Therefore, the apparent light blocking body does not affect the range in which chief rays having wavelengths included in the first wavelength range are imaged on the image sensor 30.

[0189] In contrast, the apparent light blocking body blocks light rays having wavelengths included in the first wavelength range that are emitted from points on the apparent line segment F-F' and that are imaged on the image sensor 30. Similarly, the apparent light blocking body blocks light rays having wavelengths included in the second wavelength range that are emitted from points on the apparent line segment G-G' and that are imaged on the image sensor 30.

[0190] Let f' be the point on the image sensor 30 that is conjugate to apparent position F', and g' be the point on the image sensor 30 that is conjugate to apparent position G'. Point f' is located between points b and f shown in FIG. 18, and point g' is located between points g and b shown in FIG. 18. In this case, the range in which the first image 110a and the second image 110b overlap on the image sensor 30 is the range of line segment f'-g'. Therefore, the range in which the first image 110a and the second image 110b overlap is narrowed.

[0191] 22 is a diagram schematically showing the positional relationship between the apparent light blocking body, the actual light blocking body, and the dichroic prism 10. If the actual point corresponding to the apparent point Z is Z', then the actual light blocking body 10-3 is located between point O and point Z', as shown in Fig. 22. Point Z' is located on the line segment O-B2 or O-B3 shown in Fig. 19.

[0192] 23 is a diagram schematically illustrating the area where the first light beam La and the second light beam Lb block the optical path along which they both form an image on the image sensor 30. By arranging the light blocking body 10-3 within the area indicated by the hatched triangle OB2C2 in FIG. 23, the area where the first image 110a and the second image 110b overlap on the image sensor 30 can be reduced.

[0193] When the optical path adjustment element 10-1 is positioned as shown in FIG. 3, a light shielding body 10-3 is placed between the optical path adjustment element 10-1 and the subject 110 at a position that blocks the optical path along which the first light beam La and the second light beam Lb are both imaged on the image sensor 30.

[0194] Next, a second method for narrowing the overlapping range of the first image 110a and the second image 110b will be described. The second method is to use a filter array. FIG. 24 is a diagram schematically illustrating an example of a filter array 31. As shown in FIG. 24, the filter array 31 is disposed between the imaging optical system 20 and the image sensor 30. The filter array 31 includes a first filter portion 31a and a second filter portion 31b. The first filter portion 31a transmits the first light beam La and blocks the second light beam Lb by reflection or absorption. The second filter portion 31b transmits the second light beam Lb and blocks the first light beam La by reflection or absorption.

[0195] The direction perpendicular to the imaging surface of the image sensor 30 and away from the imaging surface is defined as "up." The first filter portion 31a is disposed above a first region on the image sensor 30 that corresponds to the line segment a-b. The second filter portion 31b is disposed above a second region on the image sensor 30 that corresponds to the line segment b-c. Therefore, a first image 110a can be acquired in the first region of the image sensor 30, and a second image 110b can be acquired in the second region. When the filter array 31 is disposed directly above the image sensor 30, all of the multiple photoelectric conversion elements included in the image sensor 30 receive light having wavelengths included in either the first or second wavelength range.

[0196] When the filter array 31 is positioned away from the image sensor 30, some of the photoelectric conversion elements included in the image sensor 30 may receive light having wavelengths included in the first wavelength range and light having wavelengths included in the second wavelength range due to the influence of light that passes obliquely through the first filter portion 31 a or the second filter portion 31 b. The number of these photoelectric conversion elements can be reduced, for example, by the following method. One method is to limit the distance between the filter array 31 and the image sensor 30 relative to the size of the image sensor 30. Alternatively, one method is to increase the telecentricity of the imaging optical system 20.

[0197] The filter array 31 includes a single first filter portion 31a and a single second filter portion 31b. Therefore, the filter array 31 is easier to fabricate than a configuration in which multiple filters are formed corresponding to multiple photoelectric conversion elements. In a configuration in which multiple filters are formed corresponding to multiple photoelectric conversion elements, the positional relationship between each photoelectric conversion element and its corresponding filter is designed so that the positional deviation between them is sufficiently small compared to the size of each photoelectric conversion element. In contrast, the positional relationship between the first region and the first filter portion 31a does not need to be designed very strictly because the influence of the positional deviation between them is small. The same applies to the positional relationship between the second region and the second filter portion 31b.

[0198] [Additional Description of the Optical Path Adjustment Element 10-1] As shown in Fig. 19, unlike the apparent object, the actual subject 110 is not located on an extension of the optical axis of the imaging optical system 20. Therefore, the orientation of the imaging optical system 20 differs significantly depending on whether or not the dichroic prism 10 is provided. This problem can be solved by providing an optical path adjustment element 10-1 between the subject 110 and the dichroic prism 10. The optical path adjustment element 10-1 allows the imaging optical system 20 to be oriented in a natural direction.

[0199] The natural direction of the imaging optical system 20 is, for example, a direction in which the first image 110a and the second image 110b are formed on the image sensor 30 so as not to overlap each other, and is a direction in which the central axis of the area between the first image 110a and the second image 110b intersects with the object 110. When this direction coincides with the optical axis of the imaging optical system 20, the object 110 is located in the optical axis direction of the imaging optical system 20 and faces the image sensor 30. In this case, the first image 110a and the second image 110b of the object 110 located in that direction can be formed on the image sensor 30 so as not to overlap each other.

[0200] When the apparent subject is within the range of the line segment AB, the optical path adjustment element 10-1 can be designed, for example, so that the light beam from the midpoint of the line segment AB is parallel to the optical axis of the imaging optical system 20.

[0201] The imaging device 100 may further include an adjustment device for adjusting the positions and orientations of the optical path adjustment element 10-1 and the dichroic prism 10. Alternatively, when the optical path adjustment element 10-1 is configured from a plurality of mirrors or prisms, the imaging device 100 may further include an adjustment device for adjusting the positions and orientations of a plurality of components included in the optical path adjustment element 10-1.

[0202] Changing lenses and operating the zoom lens can change the focal length of the imaging optical system 20, which can change the range of the subject image on the image sensor 30. This can also change the center of the imaging range on the imaging surface of the image sensor 30. Even in this case, the above-mentioned adjustment tool can be used to adjust the optical axis of the imaging optical system 20 so that it passes through the center in a direction perpendicular to the imaging surface of the image sensor 30.

[0203] [Arrangement of Dichroic Prism 10] The size of the image sensor 30 is usually several millimeters to several tens of millimeters. Therefore, the area of ​​the subject 110 is often larger than the imaging surface of the image sensor 30. Therefore, each of the first and second images formed on the image sensor 30, more specifically on its imaging surface, is smaller than the subject 110. When imaging an area of ​​the subject 110 that is larger than the imaging surface of the image sensor 30, the spread angle of the light beam formed by the imaging optical system 20 is smaller on the side of the subject 110 and larger on the side of the image sensor 30.

[0204] In the imaging device 100, the dichroic prism 10 is disposed on the subject 110 side with respect to the imaging optical system 20. As a result, the aberration that occurs when a light beam having a divergence angle passes through the dichroic prism 10 can be reduced compared to a configuration in which the dichroic prism 10 is disposed on the image sensor 30 side.

[0205] [Connection of Optical Component 10A and Lens Equipment 20A] In the imaging device 100, a general commercially available lens equipment and camera can be used as the lens equipment 20A and the camera 30A. Below, an example of connection of the optical component 10A and the lens equipment 20A that makes it easy to use a commercially available lens equipment and camera will be described. The optical component 10A is detachable from the lens equipment 20A and can be connected to a commercially available lens equipment.

[0206] FIG. 25A is a schematic diagram illustrating an example of connecting an optical component 10A and a lens device 20A. The optical component 10A includes a dichroic prism 10, an optical path adjusting element 10-1, and a housing 12 that houses them. The housing 12 includes a sidewall 12a and a light-transmitting window 12b. The sidewall 12a surrounds and supports the dichroic prism 10 and the optical path adjusting element 10-1. The sidewall 12a has light-blocking properties and may function as the light-blocking body 10-2 shown in FIG. 3. The light-transmitting window 12b transmits light beams L from the subject 110. The light-transmitting window 12b is located near the front end of the sidewall 12a. The light-transmitting window 12b may be, for example, an optical filter that is transparent to first and second wavelength ranges and blocks or attenuates light beams having wavelengths included in wavelength ranges other than the first and second wavelength ranges. Alternatively, the light-transmitting window 12b may be omitted.

[0207] The housing 12 further includes a connection structure 12c located near the rear end of the side wall 12a. The connection structure 12c is a structure for connecting the optical component 10A and the lens device 20A. The connection structure 12c may be, for example, a male screw.

[0208] The lens device 20A includes an imaging optical system 20 and a lens housing 22 that houses the imaging optical system 20. The lens housing 22 may include a side wall 22a and light-transmitting windows 22b1 and 22b2. The side wall 22a surrounds and supports the imaging optical system 20. The light-transmitting windows 22b1 and 22b2 transmit the first light beam La and the second light beam Lb. The light-transmitting window 22b1 is located near the front end of the side wall 22a, and the light-transmitting window 22b2 is located near the rear end of the side wall 22a. The light-transmitting windows 22b1 and 22b2 may be formed from a light-transmitting member such as glass, or may simply be hollow.

[0209] The lens housing 22 further includes a connection structure 22c1 located near the front end of the side wall 22a and a connection structure 22c2 located near the rear end of the side wall 22a. The connection structure 22c1 is a structure for attaching a camera lens filter. The connection structure 22c2 is a structure for connecting the lens device 20A and the camera 30A. The connection structures 22c1 and 22c2 may be, for example, female screws.

[0210] The optical component 10A and the lens equipment 20A can be connected by the connection structure 12c of the optical component 10A and the connection structure 22c1 of the lens equipment 20A. The central axis of the connection structure 12c of the optical component 10A is located on the optical axis of the imaging optical system 20. The dichroic prism 10 can be fixed in the housing 12, for example, so that the central axis is included in the surface 10a2 of the dichroic prism 10. In this case, by connecting the optical component 10A and the lens equipment 20A, the plane including the surface 10a2 can include the optical axis of the imaging optical system 20.

[0211] FIG. 25B is a diagram schematically illustrating another example of connecting the optical component 10A and the lens equipment 20A. The imaging device 100 shown in FIG. 3 may further include an adjustment tool 40 shown in FIG. 25B. The adjustment tool 40 adjusts the positional relationship between the dichroic prism 10 and the imaging optical system 20. The positional relationship between the two may be, for example, the relative angle between the two. The optical component 10A and the imaging optical system 20 are connected via the adjustment tool 40. The connection structure 12c of the optical component 10A may be, for example, a female screw. The relative angle may be adjusted, for example, by adjusting the amount of threading of the female screw.

[0212] The adjustment tool 40 has a generally cylindrical shape. The adjustment tool 40 may include, for example, a complete screw 40a and a clamping ring 40b. The front end of the complete screw 40a is connected to a female screw near the rear end of the optical component 10A, and the rear end of the complete screw 40a is connected to a female screw near the front end of the lens equipment 20A. After the front end of the complete screw 40a is screwed into the female screw near the rear end of the optical component 10A to a desired position, the optical component 10A and the lens equipment 20A are fixed by the clamping ring 40b. As a result, the positional relationship between the dichroic prism 10 and the imaging optical system 20 can be adjusted to a desired positional relationship, more specifically, a desired angular relationship.

[0213] FIG. 25C is a schematic diagram illustrating yet another example of connecting the optical component 10A and the lens equipment 20A. As shown in FIG. 25C, the connecting structure 12c of the optical component 10A and the connecting structure 22c1 of the lens equipment 20A may have a flange structure similar to an ISO-KF flange, for example. The imaging device 100 shown in FIG. 3 may further include a fixing fixture 42 shown in FIG. 25C. The fixing fixture 42 may include, for example, a centering ring 42a and a clamp ring 42b. The centering ring 42a facilitates alignment of the connecting structure 12c of the optical component 10A, which has a flange structure, and the connecting structure 22c1 of the lens equipment 20A. The clamp ring 42b allows connection of the connecting structure 12c of the optical component 10A, which has a flange structure, and the connecting structure 22c1 of the lens equipment 20A. As a result, the dichroic prism 10 and the imaging optical system 20 achieve a desired positional relationship, more specifically, a desired angular relationship.

[0214] As described above, by connecting the optical component 10A and the lens equipment 20A, the dichroic prism 10 and the imaging optical system 20 can be fixed in a desired angular relationship. Furthermore, by connecting the lens equipment 20A and the camera 30A, the imaging optical system 20 and the image sensor 30 can be fixed in a desired angular relationship. Therefore, by connecting the optical component 10A, the lens equipment 20A, and the camera 30A, the dichroic prism 10 and the image sensor 30 can be fixed in a desired angular relationship. As a result, as shown in FIG. 20 , the plane 24 can be positioned so as to be parallel to the short side of the rectangular imaging range and pass through the midpoint of the long side.

[0215] If the components shown in Figures 25A to 25C are not used, the phase of the female screws provided in commercially available lens devices differs from lens device to lens device, making it difficult to fix the dichroic prism 10 and the image sensor 30 in the desired angular relationship.

[0216] As described above, according to the imaging device 100 of the first embodiment, the first image 110a and the second image 110b are mirror-symmetric to each other. This relationship allows for easy identification of corresponding positions within these two images. Because the first light beam La and the second light beam Lb travel symmetrically with respect to the plane 24 including the optical axis of the imaging optical system 20, curvature aberration and vignetting occur approximately equally in the first and second wavelength ranges. Therefore, the intensity ratio at corresponding positions within the first image 110a and the second image 110b is hardly affected by curvature aberration and vignetting. Thus, the first image 110a and the second image 110b are suitable for evaluation of the subject 110 using methods such as two-color thermography and fluorescence imaging.

[0217] Furthermore, according to the imaging device 100 of the first embodiment, commercially available lens equipment and cameras can be used as the lens equipment 20A and the camera 30A, respectively. In the imaging device 100, the optical component 10A is added to such lens equipment 20A and camera 30A. In this way, the imaging device 100 has a simple configuration.

[0218] Therefore, the imaging device 100 according to the first embodiment can acquire, with a simple configuration, two images in different wavelength ranges suitable for evaluating the subject 110. Furthermore, the imaging device 100 according to the first embodiment can also include an optical path adjustment element 10-1 disposed between the subject 110 and the dichroic prism 10. The optical path adjustment element 10-1 allows the subject 110 to be imaged in a natural orientation, in which the subject 110 is positioned in the optical axis direction of the imaging optical system 20 and faces the image sensor 30.

[0219] (Modifications of the Image Capturing Device 100 According to Embodiment 1) Modifications 1 and 2 of the image capturing device 100 according to Embodiment 1 will be described below. The first sub-component 10A1 and the second sub-component 10A2 shown in FIG. 1 are not limited to the dichroic prism 10 and the optical path adjusting element 10-1 shown in FIG. 3, respectively.

[0220] [Variation 1] FIG. 26 is a diagram schematically illustrating a specific configuration of an optical component 10A in Variation 1 of the imaging device 100 according to Embodiment 1. The optical component 10A illustrated in FIG. 26 includes an optical element group 14 and an optical path adjusting element 11-1. The optical component 10A illustrated in FIG. 26 may further include the light blocking body 10-2 and the housing 12 illustrated in FIG. 3. The optical element group 14 includes a dichroic mirror 16 having a dichroic surface 16a, two mirrors 17a and 17b, and a triangular prism 18. The optical path adjusting element 11-1 is a half pentaprism. The optical element group 14 corresponds to the first sub-component 10A1 illustrated in FIG. 1, and the optical path adjusting element 11-1 corresponds to the second sub-component 10A2 illustrated in FIG. 1. In this specification, the optical element group 14 will also be simply referred to as the "first optical element," and the optical path adjusting element 11-1 will also be simply referred to as the "second optical element."

[0221] Fig. 27 is a diagram schematically showing the optical element group 14 in Modification 1. As shown in Fig. 27, the dichroic mirror 16 is a flat optical element having a dichroic surface 16a. The dichroic surface 16a is arranged within a plane 24. The two mirrors 17a and 17b are arranged symmetrically with respect to the plane 24. An angle ε is formed between the mirror 17a and the plane 24. The same applies to the angle formed between the mirror 17b and the plane 24. However, the tilt directions of the mirrors 17a and 17b are opposite to each other.

[0222] Triangular prism 18 has a triangular prism shape and has three side surfaces: surface 18a1, surface 18a2, and surface 18a3. Surfaces 18a1 and 18a2 are arranged symmetrically with respect to plane 24. Surface 18a1 forms an angle δ with plane 24. The same applies to the angle formed by surface 18a2 and plane 24. However, surfaces 18a1 and 18a2 are inclined in opposite directions.

[0223] 28 is a diagram schematically illustrating an example of the paths of the light beam L, the first light beam La, and the second light beam Lb within the optical element group 14 in Modification 1. As shown in Fig. 28, the dichroic surface 16a of the dichroic mirror 16 reflects the first light beam La of the light beam L incident in the direction θ in the direction -θ and transmits the second light beam Lb in the direction θ. In this way, the dichroic surface 16a separates the light beam L into the first light beam La and the second light beam Lb.

[0224] The mirror 17a reflects the first light beam La to make it incident on the triangular prism 18, and the mirror 17b reflects the second light beam Lb to make it incident on the triangular prism 18. The traveling direction of the first light beam La reflected by the mirror 17a is θ-2ε, and the traveling direction of the second light beam Lb reflected by the mirror 17b is −θ+2ε.

[0225] The triangular prism 18 emits the incident first light beam La and second light beam Lb to the outside of the triangular prism 18. The first light beam La is incident on surface 18a1, is totally reflected by surface 18a2, and is emitted to the outside of the triangular prism 18 from surface 18a3. The traveling direction of the first light beam La emitted to the outside is -θ+2ε-2δ. The second light beam Lb is incident on surface 18a2, is totally reflected by surface 18a1, and is emitted to the outside of the triangular prism 18 from surface 18a3. The traveling direction of the second light beam Lb emitted to the outside is θ-2ε+2δ. The first light beam La and the second light beam Lb are symmetrical with respect to the plane 24.

[0226] As described above, the optical element group 14 separates the light beam L into the first light beam La and the second light beam Lb by the dichroic surface 16a. The optical element group 14 further converts the directions of the first light beam La and the second light beam Lb by the two mirrors 17a and 17b and the triangular prism 18, and then emits the first light beam La and the second light beam Lb.

[0227] Assume that light beam L is incident on dichroic surface 16a in a direction θ=−π / 4. When angle ε is π / 24, first light beam La is incident on surface 18a1 in a direction −π / 3, and second light beam Lb is incident on surface 18a2 in a direction π / 3. Furthermore, when angle δ is approximately π / 6, the directions of travel of first light beam La and second light beam Lb emitted to the outside are approximately zero.

[0228] Fig. 29 is a diagram schematically illustrating the optical path adjusting element 11-1 in Modification 1. As shown in Fig. 29, the optical path adjusting element 11-1 has a surface 11-1a1, a surface 11-1a2, and a surface 11-1a3. The optical path adjusting element 11-1 further has a surface 11-1a4 and a surface 11-1a5. The surfaces 11-1a4 and 11-1a5 are surfaces through which the light beam L does not pass, and may be absent.

[0229] The surface 11-1a1 and the surface 11-1a2 form an angle ρ. The surface 11-1a1 and the surface 11-1a3 form an angle μ. The surface 11-1a3 may have a metal film or a dielectric multilayer film to achieve high light reflectivity.

[0230] 30 is a diagram schematically illustrating an example of the path of the light beam L within the optical path adjusting element 11-1 in Modification 1. In the example illustrated in FIG. 30, it is assumed that the surface 11-1a1 is perpendicular to the plane 24 illustrated in FIG. 27. In the optical path adjusting element 11-1, the light beam L is reflected twice inside. Therefore, as long as the light beam L passes through the incident surface and the reflecting surface in the order described below, the orientation of the optical path adjusting element 11-1 does not affect the change in the path of the light beam L.

[0231] Light beam L is incident on surface 11-1a1. The traveling direction of light beam L incident on surface 11-1a1 is φ. Light beam L incident on surface 11-1a1 is totally reflected by surface 11-1a2. The traveling direction of light beam L totally reflected by surface 11-1a2 is -φ+π-2ρ. Light beam L totally reflected by surface 11-1a2 is totally reflected by surface 11-1a3 and emitted to the outside from surface 11-1a2. The traveling direction of light beam L emitted to the outside from surface 11-1a2 is φ+2ρ+2μ. However, this utilizes the fact that the angle remains the same regardless of a difference of ±2π.

[0232] When ρ is approximately π / 4 and μ is approximately 5π / 8, 2ρ+2μ is approximately −π / 4. Therefore, the optical path adjusting element 11-1 has the function of changing the traveling direction of the light beam L by approximately −π / 4.

[0233] 31 is a diagram schematically illustrating an example of paths of the light beam L, the first light beam La, and the second light beam Lb within the optical component 10A in Modification 1. As shown in FIG. 31 , the light beam L incident on the optical path adjustment element 11-1 in the direction φ is reflected internally and then emitted to the outside. The traveling direction of the light beam L emitted from the optical path adjustment element 11-1 to the outside is φ+2ρ+2μ.

[0234] The light beam L emitted from the optical path adjusting element 11-1 to the outside is separated into a first light beam La and a second light beam Lb by the dichroic mirror 16. The first light beam La is reflected by the mirror 17a and the surface 18a2, and then emitted from the surface 18a3. The second light beam Lb is reflected by the mirror 17b and the surface 18a1, and then emitted from the surface 18a3.

[0235] The direction of travel of the first light beam La emitted to the outside from the surface 18a3 is −φ−2ρ−2μ+2ε−2δ. The direction of travel of the second light beam Lb emitted to the outside from the surface 18a3 is φ+2ρ+2μ−2ε+2δ. Therefore, the first light beam La and the second light beam Lb are in a mirror-symmetric relationship with respect to the plane 24.

[0236] The orientation of the surface of the optical path adjustment element 11-1, the orientation of the two mirrors 17a and 17b, and the orientation of the surface of the triangular prism 18 may be set so that 2ρ + 2μ - 2ε + 2δ is approximately zero. With such settings, when the traveling direction of the light beam L incident on the optical path adjustment element 11-1 is zero, the traveling directions of the first light beam La and the second light beam Lb are also approximately zero. However, as in the first embodiment, the traveling directions of the first light beam La and the second light beam Lb do not need to be completely zero. As in the first embodiment, even when the traveling direction of the light beam L incident on the optical path adjustment element 11-1 is approximately zero, an angular difference can be imparted to the traveling directions of the first light beam La and the second light beam Lb. When the first light beam La and the second light beam Lb travel toward each other, first and second images that are mirror-symmetric with respect to the plane 24 can be formed at different positions on the image sensor 30.

[0237] In 2ρ+2μ−2ε+2δ, ρ, μ, and δ are fixed by the shapes of the optical path adjusting element 11-1 and the triangular prism 18, while ε depends on the orientations of the two mirrors 17a and 17b. Therefore, ε can be easily adjusted.

[0238] By changing ε, it is possible to move the positions of the first and second images on the image sensor 30. Therefore, the positions of the first and second images on the image sensor 30 can be set to desired positions according to the size of the subject 110, the focal length of the imaging optical system 20, and the size of the image sensor 30.

[0239] 32 is a diagram schematically illustrating an example of paths of the light beam L, the first light beam La, and the second light beam Lb in the image pickup device of Modification 1. As in Embodiment 1, as shown in FIG. 32 , by combining the optical element group 14 and the optical path adjustment element 11-1 in Modification 1 with the imaging optical system 20, the first and second images can be formed on the image sensor 30.

[0240] In the first modification, the dichroic mirror 16 is commercially available and easily available. By replacing the dichroic mirror 16, the first and second wavelength ranges can be easily changed.

[0241] Furthermore, in Modification 1, the angle between the light beam L and the dichroic surface 16a is defined as the angle of incidence, and the incident angle of the light beam L on the dichroic surface 16a can be, for example, π / 4. Therefore, compared to Embodiment 1, in which the incident angle is steep, such as π / 3, the dielectric multilayer film that constitutes the dichroic surface 16a is easier to design and manufacture.

[0242] Furthermore, in the first modification, the positions of the first and second images on the image sensor 30 can be adjusted by changing the orientations of the two mirrors 17a and 17b.

[0243] [Modification 2] Figure 33 is a diagram schematically illustrating a specific configuration of an optical component 10A in Modification 2 of the imaging device 100 according to Embodiment 1. The optical component 10A illustrated in Figure 33 includes a dichroic prism 19 and an optical path adjusting element 11-1. The optical component 10A illustrated in Figure 33 may further include the light blocking body 10-2 and housing 12 illustrated in Figure 3. The dichroic prism 19 corresponds to the first sub-component 10A1 illustrated in Figure 1, and the optical path adjusting element 11-1 corresponds to the second sub-component 10A2 illustrated in Figure 1. In this specification, the dichroic prism 19 is also referred to as the "first optical element."

[0244] Fig. 34 is a diagram schematically showing a dichroic prism 19 in Modification Example 2. As shown in Fig. 34, the dichroic prism 19 includes a first prism 19a and a second prism 19b. The first prism 19a has surfaces 19a1, 19a2, 19a3, and 19a4. The second prism 19b has surfaces 19b1, 19b2, 19b3, and 19b4.

[0245] In the first prism 19a, surfaces 19a1 and 19a2 form an angle ξ, and surfaces 19a2 and 19a3 form an angle τ. Surfaces 19a2 and 19a4 form an angle π / 2. In the second prism 19b, surfaces 19b1 and 19b2 form an angle ξ, and surfaces 19b2 and 19b3 form an angle τ. Surfaces 19b2 and 19b4 form an angle π / 2.

[0246] The surfaces 19a2 and 19b2 are bonded together with an adhesive layer. The adhesive layer is transparent to light in the second wavelength range. The surfaces 19a2 and 19b2 may be parallel to each other, for example. As a result of bonding the surfaces 19a2 and 19b2 together, the first prism 19a and the second prism 19b are arranged to be mirror images of each other.

[0247] One or both of surfaces 19a2 and 19b2 may be dichroic surfaces that reflect a first light beam La and transmit a second light beam Lb of the light beam L incident from a specific range of directions. The dichroic surfaces have the above-described function when first prism 19a and second prism 19b are bonded together. Here, the specific range of directions refers to the range of directions in which the light beam L from subject 110 is incident. Thus, dichroic prism 19 has at least one of the above-described dichroic surfaces. Surfaces 19a3 and 19b3 may have a metal film or a dielectric multilayer film to achieve high light reflectivity.

[0248] FIG. 35 is a diagram schematically illustrating an example of the paths of the light beam L, the first light beam La, and the second light beam Lb within the dichroic prism 19 in Modification Example 2. As shown in FIG. 35, the surface 19a2 of the dichroic prism 19 reflects the first light beam La of the light beam L incident in the direction θ in the direction −θ and transmits the second light beam Lb in the direction θ. In the first prism 19a, the first light beam La is totally reflected by the surface 19a3 and emitted to the outside from the surface 19a4. The traveling direction of the first light beam La emitted to the outside is θ+2ξ+2τ. In the second prism 19b, the second light beam Lb is totally reflected by the surface 19b3 and emitted to the outside from the surface 19b4. The traveling direction of the second light beam Lb emitted to the outside is −θ-2ξ-2τ.

[0249] As described above, the dichroic prism 19 separates the light beam L into the first light beam La and the second light beam Lb by the surface 19a2. The dichroic prism 19 further converts the directions of the first light beam La and the second light beam Lb by the surfaces 19a3 and 19b3 and emits them.

[0250] When θ is approximately −π / 4, ξ is approximately π / 4, and τ is approximately (7 / 8)π, the traveling directions of the first light beam La and the second light beam Lb emitted to the outside become approximately zero. Because θ is approximately −π / 4 and ξ is approximately π / 4, the light beam L can be made to enter the surface 19a1 approximately perpendicularly, and the influence of wavelength dispersion due to refraction can be reduced.

[0251] Fig. 36 is a diagram schematically illustrating an example of paths of the light beam L, the first light beam La, and the second light beam Lb within the optical component 10A in Modification 2. As shown in Fig. 36, the light beam L incident on the optical path adjustment element 11-1 in the direction φ is reflected internally and then emitted to the outside. The traveling direction of the light beam L emitted from the optical path adjustment element 11-1 to the outside is φ+2ρ+2μ.

[0252] Light beam L is incident on surface 19a1 and separated by surface 19a2 into a first light beam La and a second light beam Lb. The first light beam La is totally reflected by surface 19a3 and emitted to the outside from surface 19a4. The second light beam Lb is totally reflected by surface 19b3 and emitted to the outside from surface 19b4.

[0253] The traveling direction of the first light beam La emitted to the outside from the surface 19a4 is φ+2ρ+2μ+2ξ+2τ. The traveling direction of the second light beam Lb emitted to the outside from the surface 19b4 is −φ−2ρ−2μ−2ξ−2τ. Therefore, similar to the first embodiment and its first modification, the first light beam La and the second light beam Lb are in a mirror-symmetric relationship with respect to the plane 24.

[0254] When ρ is approximately π / 4 and μ is approximately 5π / 8, if φ is approximately zero, then φ + 2ρ + 2μ is approximately −π / 4. Furthermore, when ξ is approximately π / 4 and τ is approximately (7 / 8)π, the propagation directions of the first light beam La and the second light beam Lb are approximately zero. However, as in the first embodiment and its first modification, the propagation directions of the first light beam La and the second light beam Lb do not need to be completely zero. By adjusting any of ρ, μ, ξ, and τ, an angular difference can be imparted to the propagation directions of the first light beam La and the second light beam Lb even when φ is approximately zero. When the first light beam La and the second light beam Lb travel toward each other, first and second images that are mirror-symmetric with respect to the plane 24 can be formed at different positions on the image sensor 30.

[0255] 37 is a diagram schematically illustrating an example of paths of the light beam L, the first light beam La, and the second light beam Lb in the image pickup device according to Modification 2. As in the first embodiment and Modification 1 thereof, as shown in FIG. 37 , by combining the dichroic prism 19 and the optical path adjustment element 11-1 with the imaging optical system 20, the first and second images can be formed on the image sensor 30.

[0256] In Modification 2, the incident angle of the light beam L on the surface 19a2 is π / 4. Therefore, compared to Embodiment 1 in which the incident angle is steep, such as π / 3, the dielectric multilayer film that constitutes the surface 19a2 is easier to design and manufacture.

[0257] Furthermore, in the second modification, the surface 19a1, which is the incident surface onto which the light beam L is incident, and the surface 19a3, which is the reflecting surface that reflects the first light beam La and emits it to the outside of the dichroic prism 19, are separated. Therefore, it is not necessary to consider the total reflection condition of the first light beam La for the surface 19a1, and the restrictions on the material of the dichroic prism 19 are relaxed.

[0258] Furthermore, in Modification 2, the dichroic prism 19 is composed of a single optical element. Therefore, as compared to Modification 1 in which the optical element group 14 includes a plurality of optical elements, the dichroic prism 19 is easier to assemble and adjust.

[0259] In the first embodiment and its modifications 1 and 2, the imaging device acquires two images from a subject in different wavelength ranges as an example of two images having different optical properties. The imaging device may acquire two images from a subject having different polarization states as another example of two images having different optical properties.

[0260] Fig. 38 is a diagram schematically illustrating a specific configuration of an imaging device according to the second exemplary embodiment of the present disclosure. The imaging device 100-1 illustrated in Fig. 38 acquires two images having different polarization states from a subject 110. As illustrated in Fig. 38, the imaging device 100-1 includes an optical component 10A, a lens device 20A, and a camera 30A.

[0261] The optical component 10A includes an optical path adjustment element 11-1, a prism 19-1, and a phase plate 19c. However, the phase plate 19c is not an essential component. The lens equipment 20A includes an imaging optical system 20. The camera 30A includes an image sensor 30. The optical path adjustment element 11-1, the imaging optical system 20, and the image sensor 30 are as described above. As shown in FIG. 3, the lens equipment 20A may further include a lens housing 22 that houses the imaging optical system 20. As shown in FIG. 3, the camera 30A may further include a camera housing 32 that houses the image sensor 30. In this specification, the prism 19-1 is also referred to as a "first optical element."

[0262] The prism 19-1 shown in FIG. 38 differs from the dichroic prism 19 shown in FIG. 34 in that one or both of surfaces 19a2 and 19b2 is a polarizing beam splitter surface that reflects a first light beam La having a first polarization state and transmits a second light beam Lb having a second polarization state, among light beams L incident from directions within a specific range. The first and second polarization states are mutually different polarization states. The polarizing beam splitter surface reflects light having an electric field vector parallel to itself and transmits light having an electric field vector perpendicular to itself. In the example shown in FIG. 38, the first polarization state is S-polarized light and the second polarization state is P-polarized light. The polarizing beam splitter surface is disposed on a plane 24.

[0263] When light is incident on the polarizing beam splitter surface from a direction of approximately -π / 4, it is easy to design a film having the above function. Therefore, prism 19-1 has the shape shown in Figure 38 so that light beam L is incident on one or both of surfaces 19a2 and 19b2 from a direction of approximately -π / 4, and light beam L is incident on surface 19a1 almost perpendicularly.

[0264] However, there is a possibility that the polarization states of the incident light and the outgoing light may change as they pass through the optical path adjusting element 11-1. For example, linearly polarized light incident on the optical path adjusting element 11-1 may be changed to elliptically polarized light before being emitted. This is because reflection within the optical path adjusting element 11-1 may change the polarization state.

[0265] The phase plate 19c compensates for the change in polarization state caused by the optical path adjusting element 11-1, so that the linearly polarized light incident on the optical path adjusting element 11-1 can be made incident on the prism 19-1 as linearly polarized light.

[0266] The first light beam La and the second light beam Lb emitted from the prism 19-1 are symmetrical with respect to the plane 24. Therefore, two images having different polarization states can be simultaneously formed in mirror symmetry on the imaging surface of the image sensor 30. As a result, even in the image sensor 30 in which the sensitivity of each pixel does not have polarization dependency, it is possible to acquire two images having different polarization states. The image sensor 30 may be, for example, a normal image sensor or a hyperspectral image sensor capable of acquiring spectral information of light.

[0267] Even if the light beam L incident on the prism 19-1 is linearly polarized, the first light beam La and the second light beam Lb emitted from the prism 19-1 may become elliptically polarized after passing through the prism 19-1. Even in this case, in the image sensor 30 in which the sensitivity of each pixel does not have polarization dependency, the polarization state of the image capture result is determined only by the image position on the image sensor 30, so there is no need to compensate for the change in polarization state caused by the prism 19-1.

[0268] As described above, the image capturing device 100-1 according to the second embodiment can capture two images having different polarization states suitable for evaluating the subject 110. As explained in the first embodiment, the simple configuration and the ability to capture images in natural orientations are also achieved.

[0269] (Modifications of the Image Capturing Apparatus 100-1 According to the Second Embodiment) Modifications 1 to 3 of the image capturing apparatus 100-1 according to the second embodiment will be described below.

[0270] [Variation 1] FIG. 39 is a diagram schematically illustrating the configuration of Variation 1 of the imaging device 100-1 according to Embodiment 2. The imaging device 110-1 illustrated in FIG. 39 differs from the imaging device 100-1 illustrated in FIG. 38 in the configuration of the optical component 10A. The optical component 10A illustrated in FIG. 39 includes an optical path adjustment element 11-1, an optical path adjustment element 11-2, an optical path adjustment element 11-3, a beam splitter cube 19-2, and a phase plate 19c. However, the phase plate 19c is not an essential component. Commercially available half pentaprisms can be used as the optical path adjustment elements 11-1, 11-2, and 11-3, and a commercially available polarizing beam splitter cube can be used as the beam splitter cube 19-2. In this specification, the beam splitter cube 19-2, the optical path adjustment element 11-2, and the optical path adjustment element 11-3 are collectively referred to as the "first optical element."

[0271] The beam splitter cube 19-2 includes a prism 19-2a and a prism 19-2b, each of which is a right-angle prism, and is combined to form a rectangular parallelepiped.

[0272] Prism 19-2a has surfaces 19-2a1, 19-2a2, and 19-2a3. Surfaces 19-2a1 and 19-2a3 form a right angle. Surface 19-2a2 forms an acute angle with surface 19-2a1 and also forms an acute angle with surface 19-2a3.

[0273] Similarly, prism 19-2b has surfaces 19-2b1, 19-2b2, and 19-2b3. Surfaces 19-2b1 and 19-2b3 form a right angle. Surface 19-2b2 forms an acute angle with surface 19-2b1 and an acute angle with surface 19-2b3.

[0274] The beam splitter cube 19-2 has a polarizing beam splitter surface at the interface between the surface 19-2a2 and the surface 19-2b2. The polarizing beam splitter surface is as described above. Of the light beam L from the subject 110, the first light beam La is incident on the surface 19-2a1, reflected by the surface 19-2a2, and emitted from the surface 19-2a3. Of the light beam L from the subject 110, the second light beam Lb is incident on the surface 19-2a1, passes through the surfaces 19-2a2 and 19-2b2, and is emitted from the surface 19-2b3. A phase plate 19c that compensates for the change in polarization state caused by the light path adjustment element 11-1 may be disposed between the light path adjustment element 11-1 and the beam splitter cube 19-2.

[0275] The optical path adjustment element 11-1 changes the traveling direction of the light beam L from the subject 110, which is incident from a direction approximately parallel to the optical axis of the imaging optical system 20, by approximately −π / 4, and causes the light beam L to enter the beam splitter cube 19-2. The beam splitter cube 19-2 emits a first light beam La of the light beam L from the subject 110 in a direction whose traveling direction is reversed with respect to the polarizing beam splitter surface, and causes the first light beam La to enter the optical path adjustment element 11-2. The beam splitter cube 19-2 emits a second light beam Lb of the light beam L from the subject 110 in the same direction as the traveling direction at the time of incidence, and causes the second light beam Lb to enter the optical path adjustment element 11-3.

[0276] The optical path adjustment element 11-2 changes the traveling direction of the incident first light beam La by approximately −π / 4 and causes it to enter the imaging optical system 20. The optical path adjustment element 11-3 changes the traveling direction of the incident second light beam Lb by approximately π / 4 and causes it to enter the imaging optical system 20. By arranging the polarizing beam splitter surface on the plane 24, the first light beam La emitted from the optical path adjustment element 11-2 and the second light beam Lb emitted from the optical path adjustment element 11-3 are symmetrical with respect to the plane 24. Therefore, two images having different optical states can be formed as mirror images, and two images having different polarization states can be acquired even with the image sensor 30, in which the sensitivity of each pixel does not have polarization dependency.

[0277] [Modification 2] Fig. 40 is a diagram schematically illustrating the configuration of Modification 2 of the image pickup device 100-1 according to Embodiment 2. The image pickup device 120-1 shown in Fig. 40 enables full-Stokes imaging. The image pickup device 120-1 shown in Fig. 40 differs from the image pickup device 110-1 shown in Fig. 39 in the configurations of the optical component 10A and the camera 30A.

[0278] The optical component 10A shown in FIG. 40 includes a beam splitter cube 19-3, which is a polarization-independent beam splitter cube, instead of the beam splitter cube 19-2 shown in FIG. 39. The optical component 10A shown in FIG. 40 further includes a phase plate 19c1 arranged on the light output side of the optical path adjustment element 11-2 and a phase plate 19c2 arranged on the light output side of the optical path adjustment element 11-3, instead of the phase plate 19c shown in FIG. 39. The camera 30A shown in FIG. 40 includes a polarization image sensor 30-1 capable of measuring linearly polarized light components, instead of the image sensor 30 shown in FIG. 39. In this specification, the beam splitter cube 19-3, the optical path adjustment elements 11-2, the optical path adjustment elements 11-3, the phase plate 19c1, and the phase plate 19c2 are collectively referred to as the "first optical element."

[0279] Beam splitter cube 19-3 is the same as beam splitter cube 19-2, except that one or both of surfaces 19-2a2 and 19-2b2 are semi-transparent films. The semi-transparent films reflect half of the light beam L incident from a direction of approximately π / 4 as a first light beam La and transmit the other half as a second light beam Lb, regardless of the polarization state. The semi-transparent films are disposed on plane 24.

[0280] The optical path adjustment element 11-1 changes the traveling direction of the light beam L from the subject 110, which is incident from a direction approximately parallel to the optical axis of the imaging optical system 20, by approximately −π / 4, and causes the light beam L to enter the beam splitter cube 19-3. The beam splitter cube 19-3 emits a first light beam La of the light beam L from the subject 110 in a direction whose traveling direction is reversed with respect to the polarizing beam splitter surface, and causes the first light beam La to enter the optical path adjustment element 11-2. The beam splitter cube 19-3 emits a second light beam Lb of the light beam L from the subject 110 in the same direction as the traveling direction at the time of incidence, and causes the second light beam Lb to enter the optical path adjustment element 11-3.

[0281] The optical path adjustment element 11-2 changes the traveling direction of the incident first light beam La by approximately −π / 4 and causes it to be incident on the imaging optical system 20 via the phase plate 19c1. The optical path adjustment element 11-3 changes the traveling direction of the incident second light beam Lb by approximately π / 4 and causes it to be incident on the imaging optical system 20 via the phase plate 19c2.

[0282] The first light beam La incident on the imaging optical system 20 via the phase plate 19c1 undergoes changes in its polarization state due to passing through the optical path adjustment element 11-1, reflection at the beam splitter cube 19-3, and passing through the optical path adjustment element 11-2 before it enters the phase plate 19c1. The second light beam Lb incident on the imaging optical system 20 via the phase plate 19c2 undergoes changes in its polarization state due to passing through the optical path adjustment element 11-1, reflection at the beam splitter cube 19-3, and passing through the optical path adjustment element 11-3 before it enters the phase plate 19c2.

[0283] Therefore, the phase plate 19c1 compensates for the change in the polarization state of the first light beam La, thereby returning the polarization state of the first light beam La to the polarization state at the object 110. On the other hand, the phase plate 19c2 compensates for the change in the polarization state of the second light beam Lb, thereby returning the polarization state of the second light beam Lb to the polarization state at the object 110, and further imparts a polarization phase of π / 4 to the second light beam Lb.

[0284] In this case, the image of the first light beam La formed by the imaging optical system 20 is an image that retains the polarization state at the subject 110. The image of the second light beam Lb formed by the imaging optical system 20 is an image that is shifted in phase by π / 4 from the polarization state at the subject 110. By capturing these two images using the polarization image sensor 30-1, all components of the Stokes parameters can be acquired in a single capture. Information about the elliptically polarized light of the subject 110 can be acquired from all components of the Stokes parameters. Acquiring all components of the Stokes parameters is effective for, for example, product inspection and material analysis.

[0285] [Modification 3] Fig. 41 is a diagram schematically showing the configuration of Modification 3 of the image pickup device 100-1 according to Embodiment 2. The image pickup device 130-1 shown in Fig. 41 differs from the image pickup device 120-1 shown in Fig. 40 in the configuration of the optical component 10A.

[0286] The optical component 10A shown in Fig. 41 includes optical path adjusting elements 11-4, 11-5, and 11-6, which are metal mirrors, instead of the optical path adjusting elements 11-1, 11-2, and 11-3, which are half pentaprisms shown in Fig. 40. Changes in the polarization state occur due to reflection at dielectric interfaces, not due to reflection at metal interfaces. Therefore, the optical component 10A shown in Fig. 41 does not need to compensate for changes in the polarization state.

[0287] 41 further includes a phase plate 19c3 on the light output side of the optical path adjustment element 11-6. The phase plate 19c3 changes the polarization phase of the second light beam Lb by π / 4.

[0288] In this specification, the beam splitter cube 19-3, the optical path adjusting elements 11-5 and 11-6, and the phase plate 19c3 are collectively referred to as the "first optical element," and the optical path adjusting element 11-4 is also referred to as the "second optical element."

[0289] In the third modification, as in the second modification, all components of the Stokes parameters can be acquired in one imaging.

[0290] (Application Examples) Application examples 1 to 3 of the imaging device 100 according to the first embodiment will be described below.

[0291] 42A and 42B, temperature measurement using the image capture device 100 according to embodiment 1 will be described. Fig. 42A is a diagram schematically illustrating an example of a measurement system including the image capture device 100 according to embodiment 1. The measurement system 200A shown in Fig. 42A measures the temperature of a subject 110.

[0292] As shown in Fig. 42A , the measurement system 200A includes an imaging device 100 that images the subject 110 and a heating device 120 that heats the subject 110. The heating device 120 may locally heat a portion of the subject 110, or may heat the entire subject 110. For example, as shown in Fig. 42A , the heating device 120 may be a laser device that locally heats the subject 110 with laser light represented by a thick line. Alternatively, the heating device 120 may be a heat lamp or a resistance heater that heats the entire subject 110.

[0293] The first and second wavelength ranges are selected so that a sufficiently high thermal radiation intensity can be obtained in the temperature range for monitoring the subject 110. When the temperature range for monitoring is 200° C. or higher and 500° C. or lower and the image sensor 30 is formed from InGaAs or quantum dots, two different wavelength ranges can be selected as the first and second wavelength ranges from a wavelength range of 1.3 μm or higher and 1.6 μm or lower.

[0294] For example, two different wavelength ranges in which the emissivity of the object 110 is approximately equal may be selected as the first and second wavelength ranges. If the object 110 is made of a metal material or ceramic, the object 110 often does not have characteristic absorption in the wavelength range of 1.3 μm or more and 1.6 μm or less. If the object 110 is made of an organic material such as resin, the object 110 may have resonant absorption in the wavelength range of 1.3 μm or more and 1.6 μm or less. The wavelength range in which resonant absorption occurs has a significantly different emissivity from the surrounding wavelength ranges. Therefore, the first and second wavelength ranges may be avoided as wavelength ranges in which strong resonant absorption occurs.

[0295] The measurement system 200A may further include an auxiliary optical element that attenuates or blocks light of wavelengths outside the first and second wavelength ranges. For example, if the subject 110 is placed under illumination with visible light and the image sensor 30 is sensitive to the visible light, the measurement system 200A may further include an optical element that blocks the visible light.

[0296] When the subject 110 is heated by the heating device 120, the temperature of the subject 110 rises, generating thermal radiation according to the temperature and emissivity. FIG. 42B is a diagram schematically illustrating an example of the spectrum of thermal radiation from the subject 110. The solid line in FIG. 42B represents the spectrum in the high-temperature region of the subject 110, and the dashed line in FIG. 42B represents the spectrum in the low-temperature region of the subject 110. In the high-temperature region, thermal radiation occurs at a higher intensity at all wavelengths compared to the low-temperature region. However, the intensity ratio is greater on the short-wavelength side and smaller on the long-wavelength side. When two different wavelength ranges with approximately equal emissivity are selected as the first wavelength range 118a and the second wavelength range 118b, the ratio of the radiation intensities of the first and second wavelength ranges depends on the temperature but not on the emissivity.

[0297] Therefore, two different wavelength ranges that provide sufficient radiation intensity for imaging and have approximately equal emissivity are selected as the first and second wavelength ranges 118a and 118b. The widths of the first and second wavelength ranges 118a and 118b are approximately equal to each other.

[0298] In the measurement system 200A, a first image 110a and a second image 110b of the object 110 are simultaneously acquired, and the ratio of the radiation intensities of the first and second wavelength ranges 118a, 118b is calculated, thereby determining the temperature distribution of the object 110 regardless of the emissivity.

[0299] Measurement system 200A captures light having wavelengths included in a first wavelength range and light having wavelengths included in a second wavelength range, which are generated by thermal radiation. Measurement system 200A does not include an illumination device that emits light having wavelengths included in these wavelength ranges. Alternatively, such an illumination device is not used during temperature measurement. When ambient light that includes light having wavelengths included in the first wavelength range and light having wavelengths included in the second wavelength range, such as sunlight, is present, subject 110 and imaging device 100 may be surrounded by a light shield to prevent such ambient light from entering subject 110.

[0300] [Application Example 2: Measurement of Fluorescence Efficiency] Measurement of fluorescence efficiency using the imaging device 100 according to embodiment 1 will be described with reference to Figures 43A and 43B. Figure 43A is a diagram schematically illustrating another example of a measurement system including the imaging device 100 according to embodiment 1. Measurement system 200B shown in Figure 43A measures the fluorescence efficiency of a subject 110. The subject 110 contains a fluorescent dye that absorbs light having a wavelength included in a first wavelength range and emits light having a wavelength included in a second wavelength range. In this case, the second wavelength range is on the longer wavelength side than the first wavelength range.

[0301] The measurement system 200B includes an imaging device 100 that images the subject 110, and an illumination device 130 that emits excitation light Le as illumination light for irradiating the subject 110. When the subject 110 is irradiated with the excitation light Le, fluorescence Lf is emitted from a region of the subject 110 that has a non-zero luminous efficiency.

[0302] As the first wavelength range, a wavelength range is selected that includes the wavelength range of the excitation light Le but substantially excludes the wavelength range of the fluorescence Lf, and as the second wavelength range, a wavelength range is selected that includes the wavelength range of the fluorescence Lf but substantially excludes the wavelength range of the excitation light Le. The excitation light Le includes light having a wavelength included in the first wavelength range but does not include light having a wavelength included in the second wavelength range.

[0303] Fig. 43B is a diagram schematically showing an example of the spectra of excitation light Le and fluorescence Lf. The solid line in Fig. 43B represents the spectrum of excitation light Le, and the dashed line in Fig. 43B represents the spectrum of fluorescence Lf. The spectral width of excitation light Le is relatively narrow, and the spectral width of fluorescence Lf is relatively wide. Therefore, the width of first wavelength range 118a corresponding to excitation light Le is relatively narrow, and the width of second wavelength range 118b corresponding to fluorescence Lf is relatively wide.

[0304] The intensity of the excitation light Le on the subject 110 is distributed two-dimensionally depending on the optical characteristics of the illumination device 130 and the shape of the subject 110. The intensity of the fluorescence Lf is proportional to the intensity and luminous efficiency of the excitation light Le.

[0305] When the subject 110 is excited by excitation light Le emitted from the illumination device 130, the intensity of the excitation light Le is obtained as a first image 110a, the intensity of the fluorescence Lf is obtained as a second image 110b, and the intensity ratio between them is calculated. As a result, the distribution of the luminous efficiency of the subject 110 can be visualized regardless of the intensity distribution of the excitation light Le.

[0306] The distribution of luminous efficiency may be related to, for example, the staining density when fluorescent staining is performed on the subject 110. If the fluorescent staining is performed by a so-called antigen-antibody staining method, the concentration of the antigen can be visualized.

[0307] Alternatively, the distribution of luminescence efficiency may be related to the distribution of, for example, a quencher. The more densely the quencher is distributed in an area, the lower the luminescence efficiency. In this way, information about the concentration of the quencher can be obtained by the measurement system 200B.

[0308] 44A to 44C, visualization of a substance distribution using the imaging device 100 according to embodiment 1 will be described. Fig. 44A is a diagram schematically illustrating yet another example of a measurement system including the imaging device 100 according to embodiment 1. The measurement system 200C shown in Fig. 44A visualizes the distribution of a specific substance in a subject 110.

[0309] The measurement system 200C includes an imaging device 100 that captures an image of a subject 110, and an illumination device 140 that emits illumination light Li to illuminate the subject 110. The illumination light Li includes light having a wavelength included in a first wavelength range and light having a wavelength included in a second wavelength range. Note that if the ambient light includes light having a wavelength included in the first wavelength range and light having a wavelength included in the second wavelength range, the illumination device 140 may be omitted.

[0310] The object 110 includes at least two types of materials. The two types of materials are designated as first and second materials, where the first material has approximately equal reflectance in the first and second wavelength ranges, and the second material has significantly different reflectance in the first and second wavelength ranges. The absolute value of the difference in reflectance of the first material in the first and second wavelength ranges may be, for example, 5% or less. The absolute value of the difference in reflectance of the second material in the first and second wavelength ranges may be, for example, 10% or more. The ratio of the reflectance of the first material in the first and second wavelength ranges is different from the ratio of the reflectance of the second material in the first and second wavelength ranges.

[0311] A first image 110a and a second image 110b of a subject 110 illuminated with illumination light Li are acquired by the imaging device 100, and the intensity ratio between the two is calculated. In a region of the subject 110 where only the first substance is distributed, the intensity ratio is close to 1, whereas in a region where the second substance is distributed in large amounts, the intensity ratio deviates from 1. Therefore, the distribution of the second substance within the subject 110 can be visualized based on the intensity ratio between the two.

[0312] An example where this visualization of substances is effective is the visualization of water-soaked clothing. Figure 44B is a diagram schematically showing an example of the absorption spectrum of water. The absorption and reflection spectra of substances vary depending on the substance. When the substance is water, as shown in Figure 44B, the absorption coefficient is small in the wavelength range of 1.35 μm or less. In contrast, the absorption coefficient is large in the wavelength range of 1.4 μm to 1.5 μm. Many fibers used in clothing do not exhibit as strong wavelength dependence of the absorption coefficient as water in this wavelength range.

[0313] Therefore, when a garment includes a first wet region and a second dry region, the reflectances of the first and second regions are not significantly different in the wavelength range of 1.35 μm or less, where the absorption coefficient of water is small, whereas the reflectance of the first region is significantly lower than the reflectance of the second region in the wavelength range of 1.4 μm to 1.5 μm, where the absorption coefficient of water is large.

[0314] Therefore, a wavelength range in which the absorption coefficient of water is small is selected as the first wavelength range, and a range in which the absorption coefficient of water is large is selected as the second wavelength range. Furthermore, an illumination device 140 is used that emits light of first and second wavelength ranges as illumination light Li. Figure 44C is a diagram schematically illustrating an example of the spectrum of illumination light Li. As shown in Figure 44C, the intensities of illumination light Li in the first and second wavelength ranges 118a, 118b are approximately equal to each other. The widths of the first and second wavelength ranges 118a, 118b are approximately equal to each other.

[0315] The intensity of the illumination light Li on the subject 110 is distributed two-dimensionally depending on the optical characteristics of the illumination device 140 and the shape of the subject 110. By adjusting the illumination light Li, it is possible to match the intensity distribution on the subject 110 of light having wavelengths included in the illumination light Li within the first and second wavelength ranges 118a and 118b.

[0316] The imaging device 100 acquires a first image 110a and a second image 110b of the subject 110 illuminated with the illumination light Li, and calculates the intensity ratio between the first and second images 110a and 110b. The intensity ratio does not depend on the intensity distribution of the illumination light Li, but on the ratio of the reflectance of the subject 110 in the first and second wavelength ranges 118a and 118b. Therefore, it is possible to visualize regions of the subject 110 where the absorption coefficient of water is large, i.e., wet regions.

[0317] [Additional Notes] The above description of the embodiments discloses the following techniques.

[0318] [Technology 1] An imaging device comprising: a first optical element that separates a light beam from a subject into a first light beam and a second light beam having optical properties different from those of the first light beam; an imaging optical system in which the first light beam and the second light beam are incident at mutually different angles, the imaging optical system imaging the first light beam to form a first image and imaging the second light beam to form a second image; and an image sensor having an imaging surface, wherein the first image and the second image are formed at mutually different positions on the imaging surface, and the first image and the second image are formed on the imaging surface symmetrically with respect to a plane that intersects with the imaging surface.

[0319] This imaging device can obtain, with a simple configuration, two images having different optical characteristics suitable for evaluating a subject.

[0320] [Technology 2] The imaging device according to Technology 1, further comprising a connection structure that fixes a positional relationship between the first optical element and the imaging optical system.

[0321] In this imaging device, the dichroic prism and the imaging optical system can be fixed in a desired positional relationship, more specifically, in a desired angular relationship.

[0322] [Technology 3] The imaging device according to Technology 1 or 2, further comprising a lens housing and a camera housing, wherein the lens housing includes the imaging optical system, and the camera housing includes the image sensor, and the lens housing and the camera housing are detachable.

[0323] This imaging device allows any combination of common lens housings and camera housings.

[0324] [Technology 4] The imaging device according to any one of Technologies 1 to 3, wherein each of the first image and the second image formed on the imaging surface is smaller than the subject.

[0325] Even in the above case, this imaging device can reduce aberrations that occur when a light beam having a divergence angle passes through an optical element.

[0326] [Technology 5] The imaging device according to any one of Technologies 1 to 4, further comprising a second optical element that changes the direction of the light beam from the subject and makes the light beam incident on the first optical element.

[0327] In this imaging device, the imaging optical system can be oriented in a natural direction.

[0328] [Technology 6] The imaging device according to any one of Technologies 1 to 5, further comprising a light blocking body that blocks unintended light beams from entering the first optical element.

[0329] This imaging device can reduce stray light.

[0330] [Technology 7] The imaging device according to any one of Technologies 1 to 6, wherein the first light beam has a wavelength included in a first wavelength range, the second light beam has a wavelength included in a second wavelength range, the first optical element has a dichroic surface that reflects the first light beam and transmits the second light beam, and the dichroic surface is disposed on the plane.

[0331] This imaging device can obtain two images in different wavelength ranges as two images having different optical characteristics.

[0332] [Technology 8] The imaging device according to Technology 7, wherein the first optical element is a dichroic prism having the dichroic surface.

[0333] In this imaging device, a single dichroic prism can separate a light beam from a subject into a first light beam and a second light beam in mutually different wavelength ranges.

[0334] [Technology 9] The imaging device described in Technology 7, wherein the first optical element includes a dichroic mirror having the dichroic surface, a first mirror, a second mirror, and a triangular prism, wherein the first mirror reflects the first light beam to make it incident on the triangular prism, the second mirror reflects the second light beam to make it incident on the triangular prism, and the triangular prism emits the first light beam and the second light beam to an outside of the triangular prism.

[0335] In this imaging device, the positions of two images in different wavelength ranges on the image sensor can be adjusted by changing the orientation of the two mirrors.

[0336] [Technology 10] The imaging device according to any one of Technologies 1 to 6, wherein the first light beam has a first polarization state, the second light beam has a second polarization state, the first optical element has a polarizing beam splitter surface that reflects the first light beam and transmits the second light beam, and the polarizing beam splitter surface is disposed on the plane.

[0337] This imaging device can obtain two images having different optical characteristics, that is, two images having different polarization states.

[0338] [Technology 11] The imaging device according to claim 10, wherein the first optical element is a prism having the polarizing beam splitter surface.

[0339] In this imaging device, a single prism can separate a light beam from a subject into a first light beam and a second light beam having different polarization states.

[0340] [Technology 12] An optical component used in an imaging device including an imaging optical system and an image sensor, comprising: a first optical element that separates a light beam from a subject into a first light beam and a second light beam having optical properties different from those of the first light beam, and emits the first light beam and the second light beam symmetrically with respect to a certain plane; the first light beam and the second light beam are incident on the imaging optical system at angles different from each other; the imaging optical system forms a first image by imaging the first light beam, and forms a second image by imaging the second light beam; and the image sensor has an imaging surface, and the first image and the second image are formed at different positions on the imaging surface.

[0341] This optical component allows two images with different optical characteristics suitable for evaluating a subject to be obtained with a simple configuration using common lens equipment and a camera.

[0342] [Technology 13] The optical component according to Technology 12, further comprising a second optical element that changes the direction of the light beam from the subject and makes the light beam incident on the first optical element.

[0343] This optical component allows the imaging optics to be oriented in a natural direction.

[0344] [Technology 14] The optical component according to Technology 12 or 13, further comprising a light blocking body that blocks unintended light beams from entering the first optical element.

[0345] This optical component can reduce stray light.

[0346] [Technology 15] The optical component according to any one of Technologies 12 to 14, wherein the imaging device further includes a lens housing, the lens housing includes the imaging optical system, and the optical component is detachable from the lens housing.

[0347] The optical component can be attached to or detached from a typical lens housing.

[0348] [Technology 16] The optical component according to any one of Techniques 12 to 15, wherein the first light beam has a wavelength included in a first wavelength range, the second light beam has a wavelength included in a second wavelength range, the first optical element has a dichroic surface that reflects the first light beam and transmits the second light beam, and the dichroic surface is disposed on the plane.

[0349] This optical component allows two images to be obtained in different wavelength ranges, with two images having different optical properties.

[0350] [Technology 17] The optical component according to Technology 16, wherein the first optical element is a dichroic prism having the dichroic surface.

[0351] This optical component allows a single dichroic prism to be used to separate a first light beam and a second light beam in mutually different wavelength ranges from a light beam of an object.

[0352] [Technology 18] The optical component according to any one of Technologies 12 to 15, wherein the first light beam has a first polarization state, the second light beam has a second polarization state, the first optical element has a polarizing beam splitter surface that reflects the first light beam and transmits the second light beam, and the polarizing beam splitter surface is disposed on the plane.

[0353] This optical component allows two images with different optical properties to be obtained, that is, two images with different polarization states.

[0354] [Technology 19] A measurement system comprising: the imaging device according to any one of technologies 1 to 9; and a heating device that heats the subject.

[0355] This measurement system can measure the temperature of the object.

[0356] [Technology 20] A measurement system comprising: the imaging device according to any one of techniques 1 to 9; and an illumination device that emits illumination light for illuminating the subject.

[0357] This measurement system can measure the fluorescence emission efficiency of a subject when the subject contains a fluorescent dye.

[0358] The imaging device of the present disclosure is particularly useful for two-color thermography and fluorescence imaging. The imaging device of the present disclosure is also useful for visualizing material distribution.

[0359] 10, 19 Dichroic prism 10-1, 11-1, 11-2, 11-3, 11-4, 11-5, 11-6 Optical path adjusting element 10-2, 10-3 Light blocking body 10A Optical component 10A1 First sub-component 10A2 Second sub-component 10a First Littrow prism 10b Second Littrow prism 10a1, 10a2, 10a3, 10b1, 10b2, 10b3, 10-1a1, 10-1a2, 10-1a3, 11a2, 11-1a1, 11-1a2, 11-1a3, 11-1a4, 11-1a5, 13a1, 15 a1, 18a1, 18a2, 18a3, 19a1, 19a2, 19a3, 19a4, 19b1, 19b2, 19b3, 19b4, 19-2a1, 19-2a2, 19-2a3, 19-2b1, 19-2b2, 19-2b3 Surface 10a4, 10b4 plane 11a, 11b, 13a, 15a, 19a, 19b, 19-2a, 19-2b Prism 14 Optical element group 16 Dichroic mirror 16a Dichroic surface 17a, 17b Mirror 18 Triangular prism 19-1 Prism 19-2, 19-3 Beam splitter cube 19c, 19c1, 19c2, 19c3 Phase plate 12 Housing 12a, 22a Side wall 12b, 22b1, 22b2 Light-transmitting window 12c, 22c1, 22c2 Connection structure 20 Imaging optical system 20A Lens equipment 22 Lens housing 24 Plane 26a Front principal point 26b Rear principal point 30 Image sensor 30-1 Polarized image sensor 30A Camera 30a, 30b, 32a, 32b, 32c Range 31 Filter array 31a First filter portion 31b Second filter portion 32 Camera housing 34 Image circle 36 Imaging range 38 Reference position 40 Adjustment tool 40a Full screw 40b Tightening ring 42 Fixing tool 42a Centering ring 42b Clamp ring90A, 90B Imaging device 91 Subject 91a First image 91a1, 91a2, 91a3, 91a4, 91b1, 91b2, 91b3, 91b4 Point 91b Second image 92a, 92d Half mirror 92b, 92c Mirror 93a, 93b Band-pass filter 94 Imaging optical system 95 Image sensor 95a First image sensor 95b Second image sensor 95-1 Image circle 95-2 Imaging range 95-3 Reference position 96 Dichroic prism 100, 100-1, 110-1, 120-1, 130-1 Imaging device 110 Subject 110a First image 110b Second image 110a1, 110a2, 110a3, 110a4, 110b1, 110b2, 110b3, 110b4 Points 112, 114, 116 Object plane 118a First wavelength range 118b Second wavelength range 120 Heating device 130, 140 Illumination device 200A, 200B, 200C Measurement system L Light flux La First light flux Lb Second light flux Lc, Ld Apparent light flux Le Excitation light Lf Fluorescence Li Illumination light

Claims

1. An imaging device comprising: a first optical element that separates a light beam from a subject into a first light beam and a second light beam having optical characteristics different from those of the first light beam; an imaging optical system in which the first light beam and the second light beam are incident at different angles from each other, the imaging optical system imaging the first light beam to form a first image and imaging the second light beam to form a second image; and an image sensor having an imaging surface, wherein the first image and the second image are formed at different positions on the imaging surface, and the first image and the second image are imaged symmetrically on the imaging surface with respect to a plane that intersects the imaging surface.

2. The imaging device according to claim 1, further comprising a connection structure that fixes the positional relationship between the first optical element and the imaging optical system.

3. The imaging device according to claim 1, further comprising a lens housing and a camera housing, the lens housing containing the imaging optical system, the camera housing containing the image sensor, and the lens housing and the camera housing being detachable.

4. The imaging device according to claim 1, wherein each of the first image and the second image formed on the imaging plane is smaller than the subject.

5. The imaging device according to claim 1, further comprising a second optical element that changes the direction of the light beam from the subject and makes the light beam incident on the first optical element.

6. The imaging device according to claim 1, further comprising a light blocking body that blocks unintended light beams from entering the first optical element.

7. The imaging device of claim 1, wherein the first light beam has a wavelength included in a first wavelength range, the second light beam has a wavelength included in a second wavelength range, the first optical element has a dichroic surface that reflects the first light beam and transmits the second light beam, and the dichroic surface is disposed on the plane.

8. The imaging device according to claim 7, wherein the first optical element is a dichroic prism having the dichroic surface.

9. The imaging device described in claim 7, wherein the first optical element comprises a dichroic mirror having the dichroic surface, a first mirror, a second mirror, and a triangular prism, the first mirror reflects the first light beam and makes it incident on the triangular prism, the second mirror reflects the second light beam and makes it incident on the triangular prism, and the triangular prism emits the first light beam and the second light beam to an outside of the triangular prism.

10. The imaging device of claim 1, wherein the first light beam has a first polarization state, the second light beam has a second polarization state, the first optical element has a polarizing beam splitter surface that reflects the first light beam and transmits the second light beam, and the polarizing beam splitter surface is disposed on the plane.

11. The imaging device according to claim 10, wherein the first optical element is a prism having the polarizing beam splitter surface.

12. An optical component used in an imaging device including an imaging optical system and an image sensor, comprising a first optical element that separates a light beam from a subject into a first light beam and a second light beam having optical properties different from those of the first light beam, and emits the first light beam and the second light beam symmetrically with respect to a certain plane, wherein the first light beam and the second light beam are incident on the imaging optical system at different angles from each other, the imaging optical system images the first light beam to form a first image, and images the second light beam to form a second image, and the image sensor has an imaging surface, and the first image and the second image are formed at different positions on the imaging surface.

13. The optical component according to claim 12, further comprising a second optical element that changes the direction of the light beam from the subject and makes the light beam incident on the first optical element.

14. The optical component according to claim 12, further comprising a light shield that blocks unintended light beams from entering the first optical element.

15. The optical component according to claim 12, wherein the imaging device further includes a lens housing, the lens housing includes the imaging optical system, and the optical component is detachable from the lens housing.

16. The optical component of claim 12, wherein the first light beam has a wavelength included in a first wavelength range, the second light beam has a wavelength included in a second wavelength range, the first optical element has a dichroic surface that reflects the first light beam and transmits the second light beam, and the dichroic surface is disposed on the plane.

17. The optical component according to claim 16, wherein the first optical element is a dichroic prism having the dichroic surface.

18. The optical component of claim 12, wherein the first light beam has a first polarization state, the second light beam has a second polarization state, the first optical element has a polarizing beam splitter surface that reflects the first light beam and transmits the second light beam, and the polarizing beam splitter surface is disposed on the plane.

19. A measurement system comprising: an imaging device according to any one of claims 1 to 9; and a heating device for heating the subject.

20. A measurement system comprising: an imaging device according to any one of claims 1 to 9; and an illumination device that emits illumination light for illuminating the subject.