Spectroscopic camera

Abstract

This invention provides a spectral camera capable of capturing spectral images with suppressed ghosting effects. [Solution] The spectroscopic camera 1 comprises a plurality of planar elements including an etalon, a first lens group positioned on the object side of the etalon, a second lens group positioned on the image side of the etalon, and an image sensor that receives light that has passed from the etalon through the second lens group. Parallel light collimated by the first lens group is incident on the plurality of planar elements, and the second lens group constitutes an imaging optical system that forms an image on the image sensor of the light that has passed through the plurality of planar elements. In the plurality of planar elements into which the parallel light is incident, there are two or fewer Fresnel reflection interfaces where an anti-reflective coating is not provided.

Description

[Technical Field]

[0001] This invention relates to a spectroscopic camera. [Background technology]

[0002] An imaging camera has an optical system in which multiple lenses are arranged between the objective lens and the image sensor, and a flat-panel element may be incorporated into such an optical system. In particular, in spectroscopic cameras that have a tunable etalon in the optical system of the imaging camera, the etalon may be housed in a package housing that maintains an airtight seal inside in order to suppress mechanical shock to the etalon and the ingress of water droplets. In this case, the package housing requires an inlet section to allow incident light to pass to the etalon and an outlet section to allow outgoing light from the etalon to pass to the etalon, and flat plates such as glass are used for these inlet and outlet sections, respectively (see Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-142387 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, in a configuration where multiple planar elements are incorporated into the optical system of a spectroscopic camera and parallel light is incident on these elements, there is a problem in that light is reflected at the interface of each planar element, causing multiple reflections of light and resulting in ghosting in the spectroscopic image. [Means for solving the problem]

[0005] A spectroscopic camera according to a first aspect of the present disclosure comprises a plurality of planar elements including an etalon, a first lens group positioned on the object side of the etalon, a second lens group positioned on the image side of the etalon, and an image sensor that receives light that has passed from the etalon through the second lens group, wherein parallel light collimated by the first lens group is incident on the plurality of planar elements, the second lens group constitutes an imaging optical system that forms an image on the image sensor with light that has passed through the plurality of planar elements, and in the plurality of planar elements into which the parallel light is incident, there are two or fewer Fresnel reflection interfaces that are not provided with an anti-reflective coating. [Brief explanation of the drawing]

[0006] [Figure 1] A schematic diagram showing the general configuration of the spectroscopic camera of the first embodiment. [Figure 2] A schematic diagram showing a part of the optical system components of this embodiment. [Figure 3] A cross-sectional view showing the schematic configuration of the etalon, filter package, and bandpass filter of this embodiment. [Figure 4] A schematic diagram illustrating the mechanism of ghosting when parallel light is incident on multiple flat plate elements. [Figure 5] This figure shows an example of a simulation result visualizing the positions of the real image and ghost image when no anti-reflective coating is applied to any of the multiple flat plate elements. [Figure 6] A diagram showing the placement of the anti-reflective coating in this embodiment. [Figure 7] This figure shows an example of a simulation result indicating the position of ghost images, obtained by optically simulating the spectroscopic camera of this embodiment. [Figure 8] This figure shows the ghost reduction rate when an anti-reflective coating is applied to the Fresnel reflection interface of each planar element arranged in a spectroscopic camera. [Figure 9] A diagram showing the placement of the anti-reflective coating in the second embodiment. [Figure 10] A diagram showing the placement of the anti-reflective coating in the third embodiment. [Figure 11]This figure shows an example of a simulation result obtained by optically simulating the spectroscopic camera of the third embodiment, visualizing the positions of the real image and ghost image of the object. [Figure 12] A diagram showing the placement of the anti-reflective coating in the fourth embodiment. [Modes for carrying out the invention]

[0007] [First Embodiment] The following describes a spectroscopic camera according to the first embodiment of this disclosure. [Overall configuration of the spectroscopic camera] Figure 1 is a schematic diagram showing the general configuration of the spectroscopic camera of the first embodiment. The spectroscopic camera 1 of this embodiment comprises a camera body 10 and an interchangeable lens 20 that can be attached to or removed from the camera body 10. As shown in Figure 1, the camera body 10 comprises a camera housing 11, an optical system component 12, an image sensor 13, and a circuit board 14. The optical system component 12, the image sensor 13, and the circuit board 14 are housed within the camera housing 11.

[0008] The camera housing 11 has a space inside for housing the optical system components 12, the image sensor 13, and the circuit board 14. The camera housing 11 also has fixing mechanisms for securing each lens included in the optical system components 12, the image sensor 13, and the circuit board 14. Furthermore, the camera housing 11 has a lens mount 111 that detachably holds the interchangeable lens 20. In the spectroscopic camera 1 of this embodiment, any interchangeable lens 20 can be attached to the lens mount 111. Although not shown in Figure 1, the interchangeable lens 20 incorporates multiple lenses, and these lenses differ for each interchangeable lens 20. This makes it possible to change the imaging conditions, such as zoom magnification, for each interchangeable lens 20.

[0009] Figure 2 is a schematic diagram showing a part of the optical system component 12. As shown in FIG. 2, the optical system component 12 includes a first lens group 31 and a second lens group 32. In the following description, the optical axis L of each lens constituting the optical system component 12 is assumed to coincide with the optical axis L of the image sensor 13, and the direction along the optical axis L is defined as the Z direction (the side facing the image sensor 13 is +Z). Also, one direction orthogonal to the Z direction is defined as the X direction, and the direction orthogonal to the X direction and the Z direction is defined as the Y direction. The first lens group 31 (a part on the +Z side is shown in FIG. 2) guides the light incident from the interchangeable lens 20 to the etalon 40 and the second lens group 32. As shown in FIG. 2, the first lens group 31 includes a collimator optical system 311 that makes the incident light parallel light, and the light made parallel by the collimator optical system 311 passes through the etalon 40 and is guided from the second lens group 32 to the image sensor 13.

[0010] The etalon 40 selects and transmits a predetermined wavelength from the incident light. As a result, at the image sensor 13, the light of the predetermined wavelength that has passed through the etalon 40 is received, and a spectroscopic image is captured. Also, a plurality of flat plate elements are arranged between the first lens group 31 and the second lens group 32. Examples of the flat plate elements include the glass substrates (the first substrate 41 and the second substrate 42 described later) constituting the etalon 40, the cover glass 51 and the lid glass 52 provided on the filter package 50 (see FIG. 3) that holds the etalon 40, and the band-pass filter 60 that transmits only light in a predetermined wavelength range. Note that the description of the etalon 40, the filter package 50, and the band-pass filter 60 will be given later.

[0011] <s The second lens group 32 is an imaging optical system that forms an image of the light that has passed through the etalon 40 on the image sensor 13. For example, a telecentric optical system is constituted by a plurality of lenses.

[0012] The image sensor is an image sensor having a plurality of pixels, and outputs image information of the spectroscopic image by receiving the light guided by the optical system component 12. The circuit board 14 is equipped with circuits for controlling the drive of the image sensor 13 and the etalon 40. Although not shown in the diagram, the circuit board 14 includes recording circuits for recording various information, arithmetic circuits for executing various programs, and driver circuits for controlling the drive of the image sensor 13 and the etalon 40. Furthermore, as shown in Figure 1, multiple circuit boards 14 may be provided. In the example shown in Figure 1, there is a circuit board 14 to which a filter package 50 containing an etalon 40 is fixed, and a circuit board 14 to which an image sensor 13 is fixed. In a configuration in which the filter package 50 and the image sensor 13 are fixed to a circuit board 14, the filter package 50 and the image sensor 13 can be positioned at a desired position (fixing mechanism) in the optical system component 12 by fixing the circuit board 14 to a predetermined fixing position in the camera housing 11.

[0013] [Etalon and filter package configuration] Next, we will describe the etalon 40, the filter package 50, and the bandpass filter 60. Figure 3 is a cross-sectional view showing the schematic configuration of the etalon 40, filter package 50, and bandpass filter 60 of this embodiment. In this embodiment, the etalon 40 is housed in a filter package 50, and a bandpass filter 60 is bonded to the filter package 50, thereby integrally configuring the etalon 40, filter package 50, and bandpass filter 60.

[0014] The etalon 40 is composed of a first substrate 41, a second substrate 42, a first reflective film 43, a second reflective film 44, and an actuator 45. The first substrate 41 and the second substrate 42 are substrates that are transparent to each wavelength of the spectral image captured by the spectroscopic camera 1. For example, when capturing spectral images of predetermined wavelengths in the visible light range, they are made of glass substrates. However, when capturing spectral images in the near-infrared range with the spectroscopic camera 1, the first substrate 41 and the second substrate 42 may be made of substrates that can transmit near-infrared light, such as silicon. The first substrate 41 and the second substrate 42 are integrally formed by bonding them together with a bonding layer. In this embodiment, an etalon 40 is formed by joining a first substrate 41 and a second substrate 42, and in the etalon 40, the direction from the second substrate 42 toward the first substrate 41 is Z E Direction(+Z E )

[0015] The surface of the first substrate 41 facing the second substrate 42 is provided with a first reflective film 43 and a first electrode 451 that constitutes the actuator 45. A second reflective film 44 and a second electrode 452 constituting the actuator 45 are provided on the surface of the second substrate 42 facing the first substrate 41. The surface of the first substrate 41 facing the second substrate 42 has recesses formed on it, for example, by etching. As a result, when the first substrate 41 and the second substrate 42 are joined together, the first reflective film 43 and the second reflective film 44 face each other with a predetermined first gap G1, and the first electrode 451 and the second electrode 452 face each other with a predetermined second gap G2. On the side of the second substrate 42 opposite to the first substrate 41, for example, an annular recess is formed. Of the second substrate 42, the inside of the annular recess (the central part of the substrate) constitutes the movable part 421, and the annular recess constitutes the diaphragm part 422 that holds the movable part 421. On the second substrate 42, the second reflective film 44 is provided on the surface of the movable part 421 facing the first substrate 41. The second electrode 452 may be provided on the movable part 421, on the diaphragm part 422, or extending from the movable part 421 to the diaphragm part 422.

[0016] The actuator 45 changes the distance of the first gap G1 between the first reflective film 43 and the second reflective film 44 by applying a voltage. In this embodiment, the actuator 45 is an electrostatic actuator and is composed of a first electrode 451 provided on the first substrate 41 and a second electrode 452 provided on the second substrate 42 and facing the first electrode 451. By applying a voltage between the first electrode 451 and the second electrode 452, the diaphragm portion 422 bends due to electrostatic attraction, and the movable portion 421 is displaced toward the first substrate 41. As a result, the dimension of the first gap G1 between the first reflective film 43 and the second reflective film 44 changes, and the wavelength of light transmitted through the etalon 40 changes. Note that since the thickness of the movable portion 421 is greater than the thickness of the diaphragm portion 422, the bending of the movable portion 421, that is, the bending of the second reflective film 44, is suppressed.

[0017] The filter package 50 is a box-shaped enclosure in which the internal space is maintained in a reduced-pressure environment, and houses the etalon 40 inside. This filter package 50 is configured, for example, as shown in Figure 3, with a container-shaped base 53 and a lid glass 52, and a housing space is formed inside when the base 53 and the lid glass 52 are joined together. The base 53 is made of, for example, ceramic, and comprises a base portion 531 and a side wall portion 532. The base portion 531 is configured as a flat plate with, for example, a rectangular outer shape when viewed from the Z direction, and a cylindrical side wall portion 532 rises from the outer circumference of this base portion 531 toward the lid glass 52.

[0018] Furthermore, the base portion 531 is provided with an opening 531A that penetrates along the Z direction. When the etalon 40 is housed in the filter package 50, the opening 531A overlaps with the first reflective film 43 and the second reflective film 44 in a plan view from the Z direction. Furthermore, a cover glass 51 that covers the opening 531A is joined to the side of the base portion 531 opposite to the lid glass 52.

[0019] Furthermore, a wiring section 541 is provided on the inner surface of the base portion 531 facing the lid glass 52, to which the first electrode 451 and the second electrode 452 of the etalon 40 are connected, respectively. This wiring section 541 is connected to an external terminal section 543 on the outer surface of the base portion 531 by a through electrode 542. The external terminal section 543 is connected to a driver circuit provided on the circuit board 14 when the filter package 50 is assembled onto the circuit board 14.

[0020] The side wall portion 532 is formed in a frame shape rising from the edge of the base portion 531, and the end face opposite to the base portion 531 is a flat surface perpendicular to the Z direction, to which the lid glass 52 is joined. The lid glass 52 is a transparent member having a rectangular outer shape in plan view, and is made of glass or the like.

[0021] In the filter package 50, the etalon 40 is fixed to the side wall portion 532 of the base 53. In this case, as shown in Figure 3, one end of the first substrate 41 of the etalon 40 is fixed to the side wall portion 532 by an elastic bonding member 533, forming a cantilever structure. In other words, the other end of the etalon 40 that is not fixed to the filter package 50 is a free end, and therefore the Z-axis direction from the second substrate 42 to the first substrate 41 of the etalon 40 E The direction (along the optical axis of the etalon 40) is slightly inclined with respect to the optical axis L (Z direction) of the image sensor 13. Thus, the etalon 40 constitutes the tilt element of this disclosure. This tilt angle is between 0.5 degrees and 5.0 degrees, and is more preferably within the range of 0.5 degrees to 1.0 degree. This fixing method makes it difficult for vibrations from the filter package 50 to propagate to the etalon 40.

[0022] The bandpass filter 60 transmits light within the spectral wavelength range of the spectral image from the light transmitted through the etalon 40, while blocking other light. In other words, the wavelength λ of light transmitted through the etalon 40 is given by using the dimension d of the first gap G1 between the first reflective film 43 and the second reflective film 44, the angle of incidence θ to the etalon 40, and the order n. 2dcosθ=nλ This is expressed as follows: Here, the order n takes the value of a positive integer, and light of wavelengths corresponding to multiple orders is transmitted through the etalon 40. The bandpass filter 60 transmits wavelengths from these multiple order wavelengths to a desired wavelength range (e.g., the visible light range), and blocks light in other wavelength ranges. The bandpass filter 60 may be located before the etalon 40 (on the opposite side from the image sensor 13) or after it (on the image sensor 13 side). In this embodiment, the bandpass filter 60 is bonded to the lid glass 52, and the lid glass 52 is positioned closer to the image sensor 13 than the etalon 40.

[0023] [Anti-reflective coating applied to a flat element, and ghost suppression effect] This section explains the ghosting that occurs in the spectroscopic camera 1. Figure 4 is a schematic diagram showing the mechanism of ghost generation when parallel light is incident on multiple planar elements. Figure 5 is a diagram showing an example of simulation results visualizing the positions of the real image and ghost image of an object when no anti-reflective coating is applied to any of the planar elements. The simulation results in Figure 5 show the position of the real image of the object obtained by optical simulation of the designed optical system, and the position of the ghost image due to multiple reflections in the optical system. The "ghosting" that occurs in the spectral image of the spectroscopic camera 1 is generally caused by multiple reflections of light between multiple planar elements. In particular, as in this embodiment, when a part of the planar elements (etalon 40) is tilted with respect to the optical axis L of the image sensor 13, ghosting occurs at a position different from the position of the real image of the object. For example, in Figure 4, the dashed line P1 shows light that enters the image sensor 13 without multiple reflections between the planar elements, and this light enters point A1 on the image sensor 13. In contrast, the solid line P2 shows light that has been reflected by the second reflective film 44 or the first reflective film 43 of the etalon 40, returned to the cover glass 51 side, and been reflected again by the cover glass 51, and in this case, it enters point A2 on the image sensor 13, which is shifted from point A1. Furthermore, the solid line P3 represents the light that has passed through the etalon 40, been reflected by the lid glass 52, and then reflected again by the second reflective film 44 or the first reflective film 43 of the etalon 40. In this case, the light is incident on point A3, which is shifted from point A1 on the image sensor 13.

[0024] Thus, when light that has been multiple-reflected between a tilted plate element (tilted element) and other plate elements enters the image sensor 13, the light enters at a position shifted from its original entry point. As a result, as shown in Figure 5, a ghost G appears in the spectral image near the image of the object (real image T). Generally, when the ghost intensity is 1% or less, it is difficult to see with the human eye, and has little impact on the measurement results. Therefore, it is preferable to deposit an anti-reflective coating on the flat plate element so that ghosts G with an intensity exceeding 1% can be excluded. However, if an anti-reflective coating is not provided on the flat plate element, ghosts G with an intensity of 1% or more will appear.

[0025] To suppress ghosting in the spectroscopic camera 1, it is ideal to provide an anti-reflective coating on all the flat plate elements arranged in the spectroscopic camera 1. However, if an anti-reflective coating is applied to all planar elements, the manufacturing cost of the anti-reflective coating (for example, the cost of the film material used to form the anti-reflective coating, the labor involved in forming the anti-reflective coating, etc.) will increase accordingly. Furthermore, even if an anti-reflective coating is not applied to all planar elements, if the ghosting is at a level that is not perceptible to the human eye, for example, it will not affect the measurement. Therefore, in the spectroscopic camera 1 of this disclosure, an anti-reflective coating is applied to the planar elements as described below, with the aim of minimizing manufacturing costs and suppressing ghosting to an extent that does not affect measurement accuracy.

[0026] In other words, in this embodiment, the Fresnel reflection interfaces of the five planar elements, the first substrate 41, the second substrate 42, the cover glass 51, the lid glass 52, and the bandpass filter 60, are configured such that there are two or fewer Fresnel interfaces where an anti-reflective coating is not provided. Here, the first reflective film 43 and the first electrode 451 are provided on the surface of the first substrate 41 of the etalon 40 facing the second substrate 42, and the first reflective film 43 and the first electrode 451 are provided on the surface of the second substrate 42 facing the first substrate 41. Therefore, these surfaces of the first substrate 41 facing the second substrate 42 and the surface of the second substrate 42 facing the first substrate 41 are excluded from the formation of the anti-reflective film. In other words, the anti-reflective film is provided on 6 or 7 of the 8 surfaces: the surface of the first substrate 41 facing the lid glass 52, the surface of the second substrate 42 facing the cover glass 51, both sides (±Z planes) of the cover glass 51, both sides (±Z planes) of the lid glass 52, and both sides (±Z planes) of the bandpass filter 60.

[0027] Figure 6 shows the arrangement of the anti-reflective coating 70 in this embodiment, and Figure 7 shows an example of a simulation result that visualizes the position of ghost images obtained by optically simulating the spectroscopic camera 1 of this embodiment. In this embodiment, as described above, the anti-reflective coating 70 is provided such that there are two or fewer Fresnel reflective interfaces among the multiple flat plate elements that do not have the anti-reflective coating 70. In the example shown in Figure 6, the anti-reflective coating 70 is formed on both sides of the cover glass 51, both sides of the lid glass 52, and both sides of the bandpass filter 60. Therefore, the only Fresnel reflective interfaces that do not have the anti-reflective coating 70 are the surface of the first substrate 41 facing the lid glass 52 and the surface of the second substrate 42 facing the cover glass 51. These anti-reflective coatings 70 can be any commonly used anti-reflective coating. That is, each anti-reflective coating 70 is formed by stacking multiple optical layers with different refractive indices, and a film is deposited that has a Fresnel reflectance of 0.5% or less for the wavelength range of the spectral image captured by the spectroscopic camera 1. For example, in this embodiment, spectral images of each wavelength in the visible light range are captured by the spectroscopic camera 1. In this case, an anti-reflective coating 70 having a reflectance characteristic of 0.5% or less for the visible light range from 400 nm to 700 nm is formed.

[0028] As can be seen by comparing Figure 7 and Figure 5, when using the spectroscopic camera 1 of this embodiment, the intensity of ghosting G is significantly reduced compared to an optical system without an anti-reflective coating as shown in Figure 5.

[0029] In this embodiment, the number of Fresnel reflection interfaces on which the anti-reflective coating 70 cannot be applied among the multiple flat plate elements is two or less, and the flat plate elements on which the anti-reflective coating 70 is applied are not limited to the example shown in Figure 6. For example, the anti-reflective coating 70 may not be provided on both sides of the lid glass 52, but rather on the other flat elements, namely both sides of the cover glass 51, the surface of the first substrate 41 facing the cover glass 51, the surface of the second substrate 42 facing the lid glass 52, and both sides of the bandpass filter 60. In this configuration, an example of the spectral image obtained is omitted, but a spectral image substantially similar to that in Figure 6 can be obtained.

[0030] [Effects of this embodiment] The spectroscopic camera 1 of this embodiment includes a plurality of planar elements (cover glass 51, lid glass 52, bandpass filter 60, etalon 40) including an etalon 40, a first lens group 31 positioned on the object side of the etalon 40, a second lens group 32 positioned on the image side of the etalon 40, and an image sensor 13 that receives light that has passed from the etalon 40 through the second lens group 32. Parallel light collimated by the first lens group 31 is incident on the plurality of planar elements, and the second lens group 32 constitutes an imaging optical system that forms an image on the image sensor 13 with light that has passed through the plurality of planar elements. Furthermore, the plurality of planar elements into which the parallel light is incident are configured such that there are two or fewer Fresnel reflection interfaces where the anti-reflective coating 70 is not provided. In this configuration, the number of Fresnel reflection interfaces where the anti-reflective coating 70 is not provided is two or less, thus suppressing multiple reflections of light between the flat plate elements. This suppresses the generation of ghosting. Furthermore, manufacturing costs can be reduced compared to the case where the anti-reflective coating is provided on all flat plate elements.

[0031] In the spectroscopic camera 1 of this embodiment, the anti-reflective coating 70 is constructed by stacking multiple thin films with different refractive indices, and has a Fresnel reflectance of 0.5% or less over the wavelength range of visible light. This allows the spectroscopic camera to capture spectral images with minimal ghosting.

[0032] [Second Embodiment] Next, a second embodiment of the present disclosure will be described. In the following explanation, components already described will be denoted by the same reference numerals, and their explanations will be omitted or simplified. In the first embodiment described above, the occurrence of ghosting was suppressed by configuring the multiple flat plate elements provided in the spectroscopic camera 1 so that there are two or fewer Fresnel reflection interfaces where the anti-reflective coating 70 is not provided. In contrast, the second embodiment differs from the first embodiment in that the anti-reflective coating 70 is formed on the flat plate element located on the image side of the etalon 40.

[0033] The spectroscopic camera 1 of this embodiment has the same configuration as the first embodiment described above, with the only difference being the flat plate element on which the anti-reflective coating 70 is provided. Therefore, the spectroscopic camera 1 of the second embodiment has the same configuration as the first embodiment shown in Figures 1 to 3.

[0034] Figure 8 shows the ghost reduction rate when an anti-reflective coating 70 is applied to the Fresnel reflection interface of each planar element arranged in the spectroscopic camera 1. This figure 8 shows how much ghosting was reduced compared to when no anti-reflective coating 70 was applied to any of the planar elements. Here, in Figure 8, the surface labeled "object side" refers to the direction of the target object being imaged by the spectroscopic camera 1, that is, the -Z side surface in Figure 1, and the surface labeled "image side" refers to the direction of the image formed on the image sensor 13, that is, the +Z side surface in Figure 1. For example, "cover glass (object side)" refers to the side of the cover glass 51 opposite to the etalon 40 (-Z side), and "cover glass (image side)" refers to the +Z side surface of the cover glass 51 facing the etalon 40. Also, "etalon (object side)" refers to the -Z side of the second substrate 42. E This refers to the side surface, the surface facing the cover glass 51. "Etalon (image side)" refers to the +Z of the first substrate 41. E This refers to the side surface, specifically the surface facing the lid glass 52.

[0035] In the spectroscopic camera 1, if a Fresnel reflection interface of a planar element exists on the image side of the etalon 40, light reflected by these Fresnel reflection interfaces enters the etalon 40 from the image side. This incident light is reflected towards the image side by the first reflective film 43 of the etalon 40, which makes it highly likely to result in ghosting. On the other hand, light that enters the etalon 40 from the object side and is reflected towards the object side by the second reflective film 44 of the etalon 40 does not enter the image sensor 13, so the ghosting contribution of the planar element on the object side is reduced. Therefore, by providing the anti-reflective coating 70 to the flat plate element that is positioned on the image side of the etalon 40, the contribution to ghost reduction is higher than when the anti-reflective coating 70 is provided to the flat plate element that is positioned on the object side.

[0036] Figure 9 shows the arrangement position of the anti-reflective coating 70 in this embodiment. In this embodiment, an anti-reflective coating 70 is provided on both sides of the lid glass 52, which is a flat plate element that contributes highly to ghost reduction, that is, a flat plate element positioned on the image side of the etalon 40, and on both sides of the bandpass filter 60.

[0037] [Effects of this embodiment] The spectroscopic camera 1 of this embodiment includes a plurality of planar elements (cover glass 51, lid glass 52, bandpass filter 60, etalon 40) including an etalon 40, a first lens group 31 positioned on the object side of the etalon 40, a second lens group 32 positioned on the image side of the etalon 40, and an image sensor 13 that receives light that has passed from the etalon 40 through the second lens group 32. Parallel light collimated by the first lens group 31 is incident on the plurality of planar elements, and the second lens group 32 constitutes an imaging optical system that forms an image on the image sensor 13 with the light that has passed through the plurality of planar elements. Furthermore, an anti-reflective coating 70 is provided on the planar elements (lid glass 52, bandpass filter 60) positioned on the image sensor side (image side) of the etalon 40. This suppresses multiple reflections of light at the flat plate elements positioned on the image side of the etalon, which contribute significantly to ghost formation. As a result, similar to the first embodiment, the generation of ghosts caused by multiple reflections of light at the Fresnel reflection interface of each flat plate element can be suppressed, and manufacturing costs can be reduced compared to the case where an anti-reflective coating is provided on all flat plate elements. This suppresses multiple reflections of light at the flat plate elements positioned on the image side of the etalon 40, which contribute significantly to ghost formation. Therefore, similar to the first embodiment, it is possible to suppress the generation of ghosts caused by multiple reflections of light at the Fresnel reflection interface of each flat plate element, and manufacturing costs can be reduced compared to the case where an anti-reflective coating is provided on all flat plate elements.

[0038] [Third Embodiment] Next, a third embodiment of this disclosure will be described. In the first embodiment described above, the spectroscopic camera 1 is configured such that there are two or fewer Fresnel reflection interfaces among the multiple flat plate elements provided that do not have the anti-reflective coating 70. In the second embodiment, the generation of ghosting is suppressed by providing the anti-reflective coating 70 on the image-side flat plate element of the etalon 40. In contrast, in the third embodiment, an anti-reflective coating is provided on the flat plate element that is tilted with respect to the optical axis L among the multiple flat plate elements.

[0039] Figure 10 shows the arrangement position of the anti-reflective coating 70 in the third embodiment. Figure 11 shows an example of a simulation result obtained by optically simulating the spectroscopic camera 1 of the third embodiment, which visualizes the position of the real image and the position of the ghost image of the object. In this embodiment, as shown in Figure 10, an anti-reflective coating 70 is provided on the image-side and object-side surfaces of the etalon 40, which is tilted at an angle θ with respect to the optical axis L of the image sensor 13. That is, the +Z side facing the lid glass 52 of the first substrate 41. E The -Z plane facing the cover glass 51 of the second substrate 42. E An anti-reflective coating 70 is provided on each of the surfaces.

[0040] In this case, multiple reflections between the etalon 40 and the planar elements (e.g., the cover glass 51 and the lid glass 52) positioned before and after the etalon 40 are suppressed. In other words, multiple reflections between the first substrate 41 and the second substrate 42 of the etalon 40, which are tilted with respect to the optical axis L, and the planar elements are suppressed. As a result, as can be seen from the simulation results shown in Figure 11, the formation of ghosts G near the real image T is suppressed. In this configuration, unlike the first embodiment, there are not two or fewer Fresnel reflection interfaces where the anti-reflective coating 70 is not provided. Therefore, in reality, ghosts G with a ghost intensity of 1% or more are formed at the real image T formation position. However, since the ghosts G overlap with the real image T, their impact on measurements is extremely low.

[0041] [Effects of this embodiment] The spectroscopic camera 1 of this embodiment includes a plurality of planar elements (cover glass 51, lid glass 52, bandpass filter 60, etalon 40) including an etalon 40, a first lens group 31 positioned on the object side of the etalon 40, a second lens group 32 positioned on the image side of the etalon 40, and an image sensor 13 that receives light that has passed from the etalon 40 through the second lens group 32. Parallel light collimated by the first lens group 31 is incident on the plurality of planar elements, and the second lens group 32 constitutes an imaging optical system that forms an image on the image sensor 13 of the light that has passed through the plurality of planar elements. The optical axis (Z) of the etalon 40 is... E The direction parallel to the direction is inclined with respect to the optical axis of the image sensor 13, and an anti-reflective coating 70 is provided on the etalon 40. As a result, light reflection from the first substrate 41 and the second substrate 42 of the etalon 40 is suppressed, so that even if a ghost G is formed, the ghost will overlap with the position of the real image T, thereby reducing the impact of the ghost G on measurement accuracy.

[0042] [Fourth Embodiment] Next, a fourth embodiment of this disclosure will be described. In the third embodiment described above, an example was shown in which an anti-reflective coating 70 is provided on an etalon 40 that is tilted at an angle θ with respect to the optical axis L of the image sensor 13. However, an anti-reflective coating may also be provided on flat plate elements arranged before and after the etalon 40.

[0043] Figure 12 shows a flat plate element and an anti-reflective coating 70 provided on the flat plate element in the fourth embodiment. In this embodiment, as shown in Figure 12, an anti-reflective coating 70 is provided on the cover glass 51, which is positioned on the object side of the etalon 40 and tilted at an angle θ with respect to the optical axis L of the image sensor 13, and on the lid glass 52, which is positioned on the image side of the etalon 40. In other words, an anti-reflective coating 70 is provided on the +Z plane of the cover glass 51 and the -Z plane of the lid glass 52.

[0044] In this case, by suppressing the reflection of light at the lid glass 52, multiple reflections of light between the lid glass 52 and the first substrate 41 or the first reflection film 43 are suppressed. Similarly, by suppressing the reflection of light toward the cover glass 51 side at the second substrate 42 or the second reflection film 44, multiple reflections of light between the cover glass 51 and the second substrate 42 or the second reflection film 44 are suppressed. As a result, similar to the third embodiment, even when a ghost G with a ghost intensity of 1% or more is formed, the formation position thereof overlaps with the formation position of the real image T, and the influence degree in measurement becomes extremely low.

[0045] [Operational Effects of this Embodiment] The spectroscopic camera 1 of this embodiment includes a plurality of flat elements (cover glass 51, lid glass 52, band-pass filter 60, etalon 40) including the etalon 40, a first lens group 31 disposed on the object side with respect to the etalon 40, a second lens group 32 disposed on the image side with respect to the etalon 40, and an imaging element 13 that receives light that has passed through the second lens group 32 from the etalon 40. Parallel light collimated by the first lens group 31 is incident on the plurality of flat elements, and the second lens group 32 constitutes an imaging optical system that forms an image of the light transmitted through the plurality of flat elements on the imaging element 13. Then, the optical axis (parallel to the Z E direction) of the etalon 40 is inclined with respect to the optical axis of the imaging element 13, and an antireflection film 70 is provided on the cover glass 51 provided in the front stage of the etalon 40 and the lid glass 52 provided in the rear stage of the etalon 40. As a result, by suppressing the reflection of light between the first substrate 41 and the lid glass 52 and between the second substrate 42 and the cover glass 51, similar to the third embodiment, even when a ghost G is formed, the ghost overlaps with the position of the real image T, and the influence on the measurement accuracy due to the ghost G can be reduced.

[0046] [Modification Example] The present invention is not limited to the above-described embodiments, and includes the following modifications as long as the object of the present invention can be achieved.

[0047] [Modification Example 1] In the embodiments described above, the bandpass filter 60 is shown to be positioned closer to the image sensor 13 than the etalon 40. However, the bandpass filter 60 may also be positioned closer to the object than the etalon 40. In other words, as described in the second embodiment, the reflected light at the Fresnel reflection interface of the planar element placed on the image side of the etalon 40 is highly likely to become a ghost. For this reason, it is preferable to configure the etalon 40 so that as few planar elements as possible are placed on the image side. Therefore, by configuring the bandpass filter 60 to be placed on the object side (-Z side) of the etalon 40, the occurrence of ghosts can be suppressed more effectively.

[0048] [Differentiation 2] In the above embodiment, etalons 40, cover glass 51, lid glass 52, and bandpass filter 60 were exemplified as multiple planar elements, but other planar elements may be arranged. In this case, it is preferable to arrange the planar elements closer to the object than the etalon 40.

[0049] [Difference 3] In the above embodiments, an example was shown in which the tilt element of the present disclosure is an etalon 40, but it is not limited thereto. For example, the Z of the etalon 40 E The orientation may be maintained parallel to the optical axis L (Z direction). Alternatively, any of the flat plate elements other than the etalon 40 may be tilted elements that are inclined with respect to the optical axis L. In that case as shown in the first embodiment, the effect of ghosting can be suppressed by configuring the multiple flat plate elements so that there are two or fewer Fresnel reflection interfaces where the anti-reflective coating 70 is not provided. It is also possible to suppress the effect of ghosting, as in the second embodiment, by arranging the tilted elements in front of (on the object side of) the etalon 40. Alternatively, as in the third embodiment, the anti-reflective coating may be formed on the tilted elements, or as in the fourth embodiment, the anti-reflective coating may be formed on the flat plate elements arranged before and after the tilted elements.

[0050] [Summary of this disclosure] A spectroscopic camera according to a first aspect of the present disclosure comprises a plurality of planar elements including an etalon, a first lens group positioned on the object side of the etalon, a second lens group positioned on the image side of the etalon, and an image sensor that receives light that has passed from the etalon through the second lens group, wherein parallel light collimated by the first lens group is incident on the plurality of planar elements, the second lens group constitutes an imaging optical system that forms an image on the image sensor with light that has passed through the plurality of planar elements, and in the plurality of planar elements into which the parallel light is incident, there are two or fewer Fresnel reflection interfaces that are not provided with an anti-reflective coating. This suppresses the generation of ghosting caused by multiple reflections of light at the Fresnel reflection interface of each flat plate element, and also reduces manufacturing costs compared to the case where an anti-reflective coating is applied to all flat plate elements.

[0051] A spectroscopic camera according to a second aspect of the present disclosure comprises a plurality of planar elements including an etalon, a first lens group positioned on the object side of the etalon, a second lens group positioned on the image side of the etalon, and an image sensor that receives light that has passed from the etalon through the second lens group, wherein parallel light collimated by the first lens group is incident on the plurality of planar elements, the second lens group constitutes an imaging optical system that forms an image on the image sensor with respect to the light that has passed through the plurality of planar elements, and an anti-reflective coating is provided on one or more of the planar elements positioned on the image sensor side of the etalon. This suppresses multiple reflections of light at the flat plate elements positioned on the image side of the etalon, which contribute significantly to ghost formation. Therefore, similar to the first embodiment, the generation of ghosts caused by multiple reflections of light at the Fresnel reflection interface of each flat plate element can be suppressed, and manufacturing costs can be reduced compared to the case where an anti-reflective coating is provided on all flat plate elements.

[0052] A spectroscopic camera according to a third aspect of the present disclosure comprises a plurality of planar elements including an etalon, a first lens group positioned on the object side of the etalon, a second lens group positioned on the image side of the etalon, and an image sensor that receives light that has passed from the etalon through the second lens group, wherein parallel light collimated by the first lens group is incident on the plurality of planar elements, the second lens group constitutes an imaging optical system that forms an image on the image sensor with respect to the light that has passed through the plurality of planar elements, and at least one of the plurality of planar elements is a tilted element having an optical axis tilted with respect to the optical axis of the image sensor, and the tilted element is provided with an anti-reflective coating. This suppresses light reflection at the tilt element, so even if a ghost is formed, it will overlap with the position of the real image, thereby reducing the impact of ghosts on measurement accuracy.

[0053] A spectroscopic camera according to a third aspect of the present disclosure comprises a plurality of planar elements including an etalon, a first lens group positioned on the object side of the etalon, a second lens group positioned on the image side of the etalon, and an image sensor that receives light that has passed from the etalon through the second lens group, wherein parallel light collimated by the first lens group is incident on the plurality of planar elements, the second lens group constitutes an imaging optical system that forms an image on the image sensor with respect to the light that has passed through the plurality of planar elements, at least one of the plurality of planar elements is a tilted element having an optical axis tilted with respect to the optical axis of the image sensor, and anti-reflective coatings are provided on the planar elements positioned before and after the tilted element. As a result, even if light is reflected by the tilt element, multiple reflections of light between the tilt element and the flat plate element provided in front of it, and multiple reflections of light between the tilt element and the flat plate element provided behind it, are suppressed. This means that even if a ghost is formed, the ghost will overlap with the position of the real image, reducing the impact of ghosts on measurement accuracy.

[0054] In the spectroscopic camera according to the above embodiment, the anti-reflective coating is constructed by stacking multiple thin films, each having a different refractive index, and has a Fresnel reflectance of 0.5% or less over the wavelength range of visible light. This allows the spectroscopic camera to capture spectral images with minimal ghosting. [Explanation of Symbols]

[0055] 1...Spectroscopic camera, 12...Optical system components, 13...Image sensor, 20...Interchangeable lens, 31...First lens group, 32...Second lens group, 40...Etalon, 41...First substrate, 42...Second substrate, 43...First reflective film, 44...Second reflective film, 50...Filter package, 51...Cover glass, 52...Lid glass, 60...Bandpass filter, 70...Anti-reflective film, 311...Collimator optical system, L...Optical axis of the image sensor.

Claims

1. Multiple planar elements including an etalon, A first lens group positioned closer to the object than the aforementioned etalon, A second lens group positioned on the image side of the aforementioned etalon, The system includes an image sensor that receives light that has passed from the etalon through the second lens group, Multiple of the aforementioned flat plate elements are incident on them with parallel light collimated by the first lens group. The second lens group constitutes an imaging optical system that forms an image on the image sensor of light that has passed through the plurality of flat plate elements. A spectroscopic camera in which, among the plurality of flat plate elements into which the parallel light is incident, there are two or fewer Fresnel reflection interfaces where an anti-reflective coating is not provided.

2. Multiple planar elements including an etalon, A first lens group positioned closer to the object than the aforementioned etalon, A second lens group positioned on the image side of the aforementioned etalon, The system includes an image sensor that receives light that has passed from the etalon through the second lens group, Multiple of the aforementioned flat plate elements are incident on them with parallel light collimated by the first lens group. The second lens group constitutes an imaging optical system that forms an image on the image sensor of light that has passed through the plurality of flat plate elements. A spectroscopic camera in which an anti-reflective coating is provided on one or more of the planar elements positioned on the image sensor side of the etalon.

3. Multiple planar elements including an etalon, A first lens group positioned closer to the object than the aforementioned etalon, A second lens group positioned on the image side of the aforementioned etalon, The system includes an image sensor that receives light that has passed from the etalon through the second lens group, Multiple of the aforementioned flat plate elements are incident on them with parallel light collimated by the first lens group. The second lens group constitutes an imaging optical system that forms an image on the image sensor of light that has passed through the plurality of flat plate elements. A spectroscopic camera in which at least one of the plurality of planar elements is a tilt element having an optical axis tilted with respect to the optical axis of the image sensor, and an anti-reflective coating is provided on the tilt element.

4. Multiple planar elements including an etalon, A first lens group positioned closer to the object than the aforementioned etalon, A second lens group positioned on the image side of the aforementioned etalon, The system includes an image sensor that receives light that has passed from the etalon through the second lens group, Multiple of the aforementioned flat plate elements are incident on them with parallel light collimated by the first lens group. The second lens group constitutes an imaging optical system that forms an image on the image sensor of light that has passed through the plurality of flat plate elements. A spectroscopic camera in which at least one of the plurality of planar elements is a tilting element having an optical axis tilted with respect to the optical axis of the image sensor, and an anti-reflective coating is provided on the planar elements arranged before and after the tilting element.

5. The tilt angle between the optical axis of the tilt element and the principal ray of the parallel light is greater than 0.5 degrees. The spectroscopic camera according to claim 3 or claim 4.

6. The anti-reflective coating is constructed by laminating multiple thin films with different refractive indices, and has a Fresnel reflectance of 0.5% or less over the wavelength range of visible light. A spectroscopic camera according to any one of claims 1 to 4.

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