Miniaturized luminous flux optical system and optical device

Abstract

To provide a luminous flux separation optical system for a miniaturized multiplate camera capable of using a C mount compatible lens that is not subjected to glass correction in an infrared and visible luminous flux separation optical system.SOLUTION: In a luminous flux separation optical system, a lens mount is a mount for a lens compatible to a lens that is not subjected to glass correction, a visible light imaging element shortens a light path length of an optical axis glass material of a visible light prism within a range that does not interfere with other optical members as much as possible, an apex angle of the infrared light separation prism is reduced with a critical angle at which infrared light separated by a separation film of an infrared light separation prism is totally reflected by a reflective surface in the infrared light separation prism as a limit, the light path length shortened by the optical axis glass material of the visible light prism increases a light path length of an air part, and a flange back length due to air conversion determined in the lens mount is secured in the light path length of visible light.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a light beam splitting optical system used in optical devices such as video cameras, and in particular to a light beam splitting optical system that provides a compact prism configuration in two-chip or multi-chip cameras that split infrared light and visible light, which are useful in medical cameras, surveillance cameras, image analysis and measurement cameras, etc. [Background technology]

[0002] Endoscopic cameras, skin observation dermascopes, and microscope cameras require the separation of visible light and infrared light (including near-infrared and mid-infrared light) to obtain separate visible and infrared images in order to diagnose and observe the condition of the epidermis and affected areas. Comparing and analyzing the skin surface image obtained using visible light and the state of the interior near the epidermis using infrared light images is used to observe many skin diseases. These skin diseases, such as malignant tumors called melanoma and benign color tumors called melanocytic nevus, are difficult to distinguish from each other by surface observation alone. Especially when internal inflammation and pigmentation have spread deeper, such as in folliculitis and skin cancer, it is necessary to observe the tissue structure of the interior of the skin to more accurately distinguish between the skin diseases.

[0003] In addition, security surveillance cameras and night vision cameras use infrared light to capture images of movements in low-light environments such as at night, and use infrared images for surveillance monitoring. These surveillance cameras capture visible light images during the day, and switch to infrared images at night or in the dark, which allows for image capture under low light conditions.

[0004] Medical and surveillance cameras that use infrared and visible light, such as those mentioned above, are required to be smaller so that they can be built into endoscopes, microscopes, etc., and so that they are not noticed by the person being monitored. In this field, C-mount (industry standard) compatible lenses with short back focal lengths have come to be used in order to achieve smaller sizes, but most of these C-mount compatible lenses are designed for single-chip cameras, and are not suitable for use with multi-chip cameras such as two-chip and three-chip cameras that use prisms or other devices to separate colors and extract multiple images using multiple image sensors, due to the effects of aberrations caused by prisms and other elements.

[0005] In recent years, by miniaturizing the image size of image sensors and prisms, C-mounts have been applied to multi-chip cameras that use prisms, and C-mount compatible lenses that have been subjected to glass correction to take into account the aberration of the prism have been developed, but these lenses have the problem that the types are limited, they are expensive, and they are extremely inconvenient.In this invention, for convenience, medical cameras, surveillance cameras, military cameras, etc. will be referred to as industrial cameras, and cameras that acquire two or more types of images using two or more types of image sensors will be referred to as multi-chip cameras, but this does not limit the applications.

[0006] There are many technologies for miniaturizing multi-chip cameras that use color separation prisms by using small lenses with short back focal lengths or flange focal lengths. For example, Patent Document 1 discloses a device for miniaturizing a color separation prism to use a small lens with a back focal length of 20 mm or less, and for setting the distance between the image sensor sensor and the prism exit surface to 1 mm or more to prevent scratches on the exit surface from being picked up by the image sensor and becoming less noticeable. While there are many examples of such devices for using lenses with short back focal lengths or flange focal lengths, miniaturization itself is limited by the dimensions of the image sensor, the diameter of the lens, the physical size of the optical elements, etc., and the lenses that can be used are limited, resulting in a lack of convenience.

[0007] Furthermore, Patent Document 2 discloses a color separation prism configuration that is compatible with C-mount lenses with a short flange back length for use in endoscopes, etc. Patent Document 2 discloses a method for achieving size reduction by using a prism with a high refractive index and for making it compatible with C-mount lenses, but there is a limit to how high the refractive index can be, and such lenses that are compatible with C-mounts are expensive and have glass corrections made specifically for use with prisms, so the lenses are specific to C-mounts and there are also cost issues.

[0008] For this reason, there has been a demand for a compact prism configuration that allows for the use of relatively inexpensive lenses that do not have glass compensation for prisms in multi-sensor industrial cameras without any restrictions.In other words, if lenses compatible with single-sensor C-mounts that essentially have no glass compensation could be used in multi-sensor industrial cameras that capture multiple images using prisms or the like, a wide variety of lenses would become available, allowing for the construction of cheaper and more convenient industrial camera systems.

[0009] To solve these problems, the applicant of the present application proposed in Patent Document 3 an invention in which the length of the optical axis glass material of the visible light side prism of a prism configuration that separates incident light into infrared light and visible light is shortened to a extent that does not interfere with other optical components. However, even when using the invention of Patent Document 3, the number of lenses that do not have glass correction that can be used is limited, so there is a demand for a more compact separating prism configuration for multi-chip cameras that can be used with a wider range of lenses that do not have glass correction. The present invention is an improved invention that further evolves based on Patent Document 3. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Publication number 07-22641 [Patent Document 2] Japanese Patent Application Publication No. 2017-205492 [Patent Document 3] Patent Publication No. 2021-44790 Summary of the Invention [Problem to be solved by the invention]

[0011] Therefore, the problem that the present invention aims to solve is to provide a light beam separation optical system for a multi-chip camera that is capable of widely using a wide variety of convenient, uncorrected lenses in an infrared and visible light separation optical system.

[0012] Furthermore, a further problem that the present invention aims to solve is to provide a light beam separation optical system with a more compact prism configuration that is suitable for cameras where miniaturization is desired, such as endoscopes, surveillance cameras, drive recorders, and smartphones. [Means for solving the problem]

[0013] In order to solve the above problems and achieve the above object, the light beam separating optical system according to the present invention is a light beam separating optical system having a lens mount, an infrared light separating prism that separates incident light into infrared light and visible light, an infrared light imaging element that converts the infrared light into an infrared light image, a visible light prism arranged after the infrared light separating prism, and a single-plate visible light imaging element that converts the visible light into a visible light image, wherein the lens mount is a lens mount that is compatible with a lens that has not undergone glass correction, and the optical axis of the visible light prism The optical path length of the glass material is shortened as much as possible within the range where the visible light imaging element does not interfere with other optical components, the apex angle of the infrared light separating prism is reduced up to the critical angle at which the infrared light separated by the separating film of the infrared light separating prism is totally reflected by the reflecting surface within the infrared light separating prism, and the optical path length of the air portion is increased to compensate for the optical path length shortened by the optical axis glass material of the visible light prism, so that the flange back length in air equivalent defined for the lens mount is ensured in the optical path length of the visible light.

[0014] In addition, the light beam separation optical system according to the present invention can also be configured so that the incident light beam entering the infrared light separation prism is not totally reflected by the separation film surface of the infrared light separation prism, and the apex angle of the infrared light separation prism is reduced up to the critical angle at which the infrared light beam separated by the separation film surface is totally reflected by the reflection surface within the infrared light separation prism.

[0015] Furthermore, the light beam separating optical system according to the present invention can also be configured so that the length of the prism glass material on the visible light side is shortened by using unnecessary light suppression grooves provided in the infrared light separating prism to avoid interference with the visible light imaging element.

[0016] Furthermore, the light beam separating optical system according to the present invention can also be configured so that the lens that is compatible with the lens mount is a C-mount lens that requires little optical correction for the thickness of the glass inserted on the image-forming side and has a short optical separating glass length on the image-forming side.

[0017] Furthermore, the light beam separating optical system according to the present invention can be used to construct an optical device. The above-mentioned means for solving the problems can be used in combination as much as possible. [Effects of the Invention]

[0018] In the light beam separating optical system of the present invention, the length of the optical path of a prism with a refractive index greater than 1 is shortened as much as possible in the visible light side prism without interfering with the infrared light side component, and the remaining portion necessary to ensure the flange back air equivalent length is made of air, and the apex angle of the infrared light separating prism is reduced, thereby further shortening the visible light optical path length. By significantly shortening the prism portion, the effects of aberration are greatly reduced even when using a single-plate C-mount lens without glass correction, making it possible to use it in practice.

[0019] The wide variety of single-chip C-mount lenses currently available on the market are C-mount lenses that do not require glass correction because they do not require the use of a prism. Many C-mount compatible lenses have little optical correction for the glass thickness inserted on the image side, resulting in lenses with a short optical separation glass length on the image side. If these lenses could be used in multi-chip cameras that use prisms, a wide variety of lens replacements would become possible at low cost. Furthermore, by shortening the prism optical path length on the visible light side, which has a refractive index greater than 1, and extending the remaining optical path length through air, which has a refractive index of 1, to ensure a sufficient flange back length, the light beam splitting optical system can be made more compact. In the present invention, the prism portion on the visible light side is simply shortened, eliminating the need for an expensive high-index prism and enabling the light beam splitting optical system to be made more compact without increasing component costs.

[0020] Furthermore, in the light beam separating optical system of the present invention, by reducing the apex angle of the infrared light separating prism and utilizing unwanted light suppression grooves such as ghost cut grooves provided in the infrared light separating prism, the length of the prism glass material can be shortened without the visible light side imaging element interfering with the infrared light separating prism, etc., thereby further shortening the prism portion and enabling a configuration in which aberrations are less affected even when using a single-plate C-mount lens that does not essentially perform glass correction, thereby enabling the configuration of an inexpensive light beam separating optical system with a simple configuration and providing optical equipment such as a convenient, miniaturized industrial camera. Furthermore, a larger imaging element can be used without having to intentionally downsize the visible light side imaging element, and there is no limit to the degree of freedom in selecting the imaging element. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram illustrating a conventional light beam splitting optical system using a general-purpose splitting prism. [Figure 2] 1 is a schematic explanatory diagram of a light beam separating optical system according to a first embodiment of the present invention. [Figure 3] FIG. 10 is a schematic explanatory diagram of a light beam separating optical system according to a second embodiment of the present invention. [Figure 4]FIG. 10 is a schematic explanatory diagram of internal reflection of an infrared light separation prism in Example 2 of the present invention. [Figure 5] FIG. 10 is a schematic explanatory diagram of a light beam separating optical system according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described with reference to the drawings. All drawings described in the following examples are drawn as schematic diagrams for the purpose of explaining the present invention, and the actual dimensions and shapes are not particularly limited. Furthermore, the dimensions, materials, shapes, relative positions, etc. of the components are not intended to limit the technical scope of the invention unless otherwise specified.

[0023] Figure 1 is a schematic diagram showing an example of a conventional infrared and visible light separation optical system using a separation prism. It shows a cross section of a two-plate infrared / visible light separation prism equipped with an imaging element that separates infrared light and visible light and extracts infrared and visible light images. A lens exchange mount 1 allows various interchangeable lenses to be used, and the light beam collected by the lens enters an infrared / visible light separation prism (infrared light separation prism) 2. The light beam incident on the infrared light separation prism 2 is reflected by separation surface 3, with the infrared wavelength R reflected by reflective surface 4 of the prism 2. The light beam then passes through exit surface 5 and enters an infrared light imaging element 6, which is installed parallel to the exit surface, and outputs the infrared light image as an electrical signal.

[0024] This infrared / visible light separating surface 3 is made of a dielectric multilayer film or a metal thin film, and reflects infrared light (including near-infrared light and mid-infrared light) and transmits visible light. Depending on the purpose of use, such a separating prism separates infrared light with a wavelength of 600 to 700 nm or more as reflected light and transmits wavelengths in the visible light range.

[0025] The transmitted light (visible light) T that passes through the separation surface 3 enters a prism 7 located after the infrared light separation prism 2, and then enters a visible light imaging element 9 arranged parallel to the exit surface 8 of the prism 7, outputting a visible light image as an electrical signal. The output visible light image may be a black-and-white image or a color image depending on the intended use. In such a prism configuration, various filters can be inserted in the optical path or on the exit side of each prism to correct output characteristics, prevent reflection, and suppress unnecessary light.

[0026] In such a prism configuration, each lens mount specifies the flange back optical path length (La+Lb) (in air) between the flange back reference plane A and the infrared and visible light imaging element plane B. For example, the C-mount, known as a compact lens mount, is specified as 17.526 mm. This flange back length is the optical path length in air terms, and if a member with a refractive index different from that of air, such as a filter, glass, or prism, is inserted in the optical path, the optical path length will change depending on the thickness and refractive index of the member.

[0027] Because the refractive index of materials inserted into the optical path, such as glass or prisms, is greater than 1, the optical path length is longer than the air-equivalent optical path length. Therefore, when miniaturization is the goal, high-index prisms are used. In a general-purpose prism, as shown in Figure 1, the light beam enters the prism, exits, and is composed almost entirely of prism materials, with refractive indices typically ranging from 1.5 to 1.8. In a conventional two-plate prism configuration, the infrared and visible light prisms are each equipped with respective image sensors via trimming filters or other filters appropriate for the intended application. Multi-plate industrial cameras, which use prisms to separate the light beam and capture multiple images, typically use C-mount lenses with glass correction to reduce the effects of prism aberration. [Example]

[0028] 2 is a schematic diagram of a two-plate light beam separation optical system for separating infrared light and visible light according to a first embodiment of the present invention. Various interchangeable lenses 10 are interchangeable using a lens interchange mount 11, and the light beam collected by the lens 10 enters an infrared / visible light separation prism (infrared light separation prism) 12. The light beam incident on the prism 12 has wavelengths in the infrared band reflected by separation surface 13, is totally reflected by reflecting surface 14 of the prism 12 as reflected light R, and enters infrared light imaging element 16, which is provided parallel to the exit surface, via exit surface 15, and outputs an infrared light image as an electrical signal.

[0029] Furthermore, transmitted light (visible light) T that has passed through separation surface 13 enters prism 17, which is arranged downstream of separation prism 12, and passes through exit surface 18 and air gap 19 of prism 17 to a visible light imaging element 20 that is arranged parallel to the exit surface, outputting a color or black-and-white visible light image as an electrical signal. Here, the optical path length of prism 17 on the visible light side is shortened to Lb' from the conventional prism length Lb in Figure 1, and the flange back length of lens interchangeable mount 11 is maintained by adjusting air gap 19 (optical path length Lc) accordingly.

[0030] 2, visible light side prism 17 is shortened by being brought as close as possible to separation prism 12 without mutual interference, and the flange back length is secured by adjusting air gap 19 and air gap La from the flange back reference plane to the prism entrance surface. Here, because the flange back length is calculated in terms of air, the prism (or glass) portion having a refractive index greater than the refractive index of 1 in air (strictly speaking, a vacuum) is shortened and the air gap portion having a refractive index of 1 is extended, so that the actual dimension (La+Lb'+Lc) between flange back reference plane A and image sensor reference plane B shown in Fig. 2 is shorter than the actual dimension (La+Lb) between flange back reference plane A and image sensor reference plane B shown in Fig. 1.

[0031] The percentage reduction in the visible light optical path length in this prism section varies depending on the infrared light separation prism, C-mount lens standard, and image sensor dimensions, but with available general prism components, it is possible to reduce the prism section of the conventional configuration by approximately 30 to 40%. With this configuration, the prism length on the visible light side is reduced to the point where single-chip C-mount lenses without glass correction can be used, making it possible to configure an optical system that is inexpensive and does not pose a problem with aberrations even when using a wide variety of single-chip industrial C-mount lenses.

[0032] Here, the single-plate C-mount lens 10 suitable for the present invention is assumed to have little optical correction for the glass thickness inserted on the image-forming side and a short optical separation glass length on the image-forming side. Such lenses are generally referred to as lenses without glass or prism correction and are widely available commercially. Since they are single-plate lenses (lenses for one imaging element) that do not require multiple color separations using prisms or the like, there are many lenses that do not require prism glass correction.

[0033] The optical path length on the infrared side can also be shortened to a degree that does not interfere with components such as the prism and image sensor on the visible side. However, because infrared light has a longer wavelength than visible light and is significantly affected by focal length, and because the focus itself is almost impossible due to the effects of chromatic aberration on the infrared light path, shortening the prism length is not prioritized. In other words, in the present invention, the optical path lengths on the visible side and the infrared side are configured differently, and priority is given to shortening the prism length on the visible side as much as possible. By shortening the prism length so that it does not interfere with the infrared prism components and the visible light side components, it is possible to use commercially available single-plate C-mount lenses that do not essentially undergo glass correction. Therefore, in the prism configuration examples of the present invention, the optical path length on the infrared side is longer than that on the visible light side. [Example]

[0034] Furthermore, in the present invention, in order to further shorten the optical path length of the prism portion of the visible light path in the infrared light splitting prism 12 and the visible light prism 17, the apex angle of the infrared light splitting prism 12 is made smaller to shorten the optical path length of the visible light in the prism portion. Figure 3 shows that the infrared light splitting prism 12 can be made shorter by making the apex angle 40 (θ) smaller than that of a conventional prism (shown by the dotted line). TIFF2025160061000002.tif9166.

[0035] Traditionally, the apex angle θ of the infrared light separating prism 12 was limited by factors such as the physical dimensions of the infrared light imaging element 16, the refractive index of the glass material, and the F-number (maximum aperture) of the lens used. Most conventional apex angles were set at approximately 26° (for a glass material such as BK7 with a refractive index of 1.51 and a wavelength of 587.6λ / nm). However, recent advances in the miniaturization of infrared light imaging elements and the adoption of high-index glass materials with high refractive indexes have made it possible to shorten the apex angle of the infrared light separating prism. Reducing the apex angle θ of the infrared light separating prism 12 changes the reflected light beam from the infrared light separating film 13 and the reflecting surface 14 within the prism, so it is necessary to efficiently capture the infrared light beam under appropriate conditions.

[0036] The conditions for the apex angle 40 (θ) of the prism 12 applied to the present invention will be described with reference to Figure 4. In Figure 4, the infrared light separating prism 12 is a cross-sectional view of a triangular prism cut at the center of the incident light beam. The central light beam C of the incident light beam is perpendicularly incident on the incident surface of the prism 12, and the infrared light beam R is reflected at an angle α by the infrared light separating film 13 (point c), while the visible light beam T is transmitted. The infrared light beam R reflected by the infrared light separating film 13 (point c) is totally reflected at an angle 2α by a reflecting surface 14 (point d) inside the prism, and is emitted from the exit surface 15 perpendicular to the infrared light beam R and enters the infrared light imaging element 16.

[0037] The reflection condition for this infrared light beam is to reduce the apex angle θ of the infrared light splitter prism 12 up to the critical angle at which the infrared light beam is totally reflected by the reflecting surface 14 (point d) within the infrared light splitter prism 12. If the apex angle θ is reduced beyond the critical angle, the optical path length of visible light in the infrared light splitter prism 14 portion is shortened, but some of the infrared light begins to exit the reflecting surface 14, reducing the amount of infrared light beam incident on the infrared imaging element 16 and affecting the contrast of the infrared image. The critical angle δ of this central light beam C is determined by the following equation (1) based on the refractive index of the infrared light splitter prism used and the air:

[0038]

number

[0039] On the other hand, in a lens configuration with a short flange back and a large lens diameter, the convergence angle θ' of the incident light beam becomes large, which restricts the condition for the apex angle θ of the infrared light splitting prism 12. In such a case, at the upper part (light beam A) and the lower part (light beam B) of the incident light beam in the figure, light beam A and light beam B are incident on the entrance surface of the prism 12 at a convergence angle θ' rather than perpendicular to the surface. In Figure 4, light beam A and light beam B are symmetrical from top to bottom in the figure and have the same convergence angle θ'. Light beam A enters the infrared light prism 12 at the convergence angle θ', and the infrared light beam is split and reflected by the infrared light splitting film 13 (point a), reflected by the reflecting surface 14 (point e) within the prism 12, and emitted from the exit surface 15. Furthermore, the B light beam incident on the infrared light prism 12 at a convergence angle θ' is separated and reflected by the infrared light separation film 13 (point b), reflected by the reflecting surface 14 (point f) within the prism 12, and emitted from the exit surface 15.

[0040] In other words, for the incident light beams A and B with a large convergence angle θ', they must be set so that they do not undergo total reflection at the infrared light separation film 13 (points a and b) but rather at the reflective surface 14 (points e and f) within the prism. As can be seen from Figure 4, for the upper part of the figure (light beam A), as the apex angle θ of the infrared light separation prism 12 is reduced, the critical angle for total reflection at the reflective surface 14 (point e) within the prism decreases. Therefore, for a lens with a large convergence angle θ', the critical angle for total reflection at the reflective surface 14 (point e) becomes the limit for reducing the apex angle θ of the infrared light separation prism 12. Furthermore, for the infrared / visible light separation film 13 (points a and b) of the infrared light separation prism 12, if the refractive index of the prism placed downstream is significantly different from that of the infrared light separation prism 12, due to factors such as the influence of adhesive, or if air other than a prism is placed downstream, total reflection may occur, so the film must be set within a range that does not cause total reflection.

[0041] For this reason, the apex angle θ of the infrared light splitting prism 12 must be reduced up to the critical angle at which incident light is not totally reflected by the infrared light splitting film 13 (points a and b) but is totally reflected by the reflecting surface 14 (points e and f) within the infrared light splitting prism 12. Under these conditions, the apex angle θ of the infrared light splitting prism 12 is reduced. TIFF2025160061000004.tif10167The apex angle θ of the light separation prism 12 is approximately 20° (glass material BK7), which is expected to be a reduction of approximately 20% compared to conventional prisms.This further shortens the visible light path length in the prism of the present invention, and has the effect of expanding the possibility of using lenses without glass correction.

[0042] As mentioned above, by shortening the prism transmission portion on the visible light path side, it becomes possible to use single-plate interchangeable lenses that do not have glass correction. The use of such interchangeable lenses not only enables a wide variety of uses for industrial cameras, but also reduces costs. Furthermore, by prioritizing the shortening of the prism portion on the visible light side and ensuring the flange back length by using an air gap, the length on the visible light side can be shortened, enabling compactness.

[0043] Furthermore, as described above, in the present invention, priority is given to shortening the optical path length of visible light, and there are cases in which the optical path length of infrared light is longer than the optical path length of visible light. However, by reducing the apex angle θ of the infrared light separation prism 12, the optical path length of infrared light is also shortened as a result, and becomes closer to the optical path length of visible light and closer to the flange back length. [Example]

[0044] 5 is a schematic diagram of a two-plate light beam splitting optical system that separates infrared light and visible light according to a third embodiment of the present invention. The same reference numerals are used to designate parts that correspond to the light beam splitting optical system in FIG. 2. In the third embodiment, the unnecessary light suppression grooves 30 provided in the infrared light splitting prism 12 are used to further shorten the prism module configuration.

[0045] Of the light beams incident on the infrared splitting prism 12, the infrared light is reflected by the infrared light splitting surface 13 as reflected light R, and the visible light is transmitted as transmitted light T. The transmitted visible light T enters the visible light imaging element 20 via a visible light prism 17 provided after the infrared light splitting prism.

[0046] 2 as much as possible, the visible light imaging element 20 is installed directly with the visible light prism 17, or via a desired filter 31 such as a trimming filter or a very small air gap. If the air gap 19 is omitted or significantly shortened and the visible light prism 17 is shortened, the imaging element 20 will interfere with the infrared separation prism 12, but in Example 3, unwanted light suppression grooves 30 are provided so that the imaging element 20 can fit in.

[0047] The main purpose of these unwanted light suppression grooves 30 is to cut infrared ghosts, and an example is shown in which the unwanted light suppression grooves 30 cut out ghost light indicated by dotted lines G. The unwanted light suppression grooves 30 are formed in locations that do not affect the optical path in the infrared light separation prism 12 so as to prevent reflected ghost light from entering the imaging element. Various shapes have been considered for this type of unwanted light suppression groove 30, but a V-shaped notch is provided so that the visible light imaging element 20, which is provided with a trimming filter 31 sandwiched between it and the infrared light prism 12 while the visible light side prism 17 is shortened as much as possible.

[0048] In industrial cameras, it is desirable to be able to use image sensors ranging from full size to small sizes depending on the purpose of the visible light image sensor 20. By forming the unwanted light suppression grooves 30 of the infrared prism 17 as described above, there are fewer restrictions on the size of the image sensor 20 even if the visible light side prism 17 is shortened, and the freedom of choice of image sensor is increased.

[0049] As explained above, according to the present invention, by shortening the prism portion on the visible light side, it is possible to use relatively inexpensive interchangeable lenses that are compatible with a wide variety of C-mounts that are not essentially subjected to glass correction, even though it is a multi-plate camera that uses a prism, and because the prism configuration of the infrared and visible light separating type is made more compact, the range of uses and applications for various industrial cameras and the like is expanded, and convenience is increased. [Industrial Applicability]

[0050] In the present invention, an example has been described assuming a two-plate separating prism that uses a C-mount lens and separates infrared light from visible light, but cameras using the optical system of the present invention can be widely applied to cameras that extract and use infrared light, such as multi-plate video cameras and still image cameras for surveillance, microscopes, telescopes, and military use, as well as mounts other than C-mount lenses. The present invention is not limited to the scope disclosed in the above example, and can be widely applied to devices that use a light beam separating optical system by appropriately combining multiple components within the scope of the claims, and has great industrial utility and applicability. [Explanation of symbols]

[0051] 10 Interchangeable Lenses 11 Camera Mount 12 Infrared light separation prism 13 Infrared light separation surface (separation membrane) 14 Infrared light reflecting surface 16 Infrared imaging element 17 Visible Light Prism 19 Air gap 20 Visible light imaging element 30 Unwanted light suppression groove 31 filters 40 Apex angle (θ) of infrared light separation prism

Claims

1. A light beam separating optical system including a lens mount, an infrared light separating prism that separates incident light into infrared light and visible light, an infrared light imaging element that converts the infrared light into an infrared light image, a visible light prism that is arranged after the infrared light separating prism, and a single-plate visible light imaging element that converts the visible light into a visible light image, the lens mount is a lens mount adapted for a lens without glass correction; the optical path length of the optical axis glass material of the visible light prism is shortened as much as possible within a range in which the visible light imaging element does not interfere with other optical members; reducing the apex angle of the infrared light splitting prism to a critical angle at which the infrared light split by the splitting film of the infrared light splitting prism is totally reflected by a reflecting surface within the infrared light splitting prism; A light beam separating optical system characterized by a configuration in which the optical path length of the air portion is increased to compensate for the optical path length shortened by the optical axis glass material of the visible light prism, so that the flange back length in air equivalent defined for the lens mount is ensured in the optical path length of the visible light.

2. 2. The light beam splitting optical system according to claim 1, wherein the incident light beam incident on the infrared light splitting prism is not totally reflected by the splitting film surface of the infrared light splitting prism, and the apex angle of the infrared light splitting prism is reduced up to the critical angle at which the infrared light beam split by the splitting film surface is totally reflected by the reflecting surface within the infrared light splitting prism.

3. 3. The light beam separating optical system according to claim 1, wherein the length of the prism glass material on the visible light side is shortened by avoiding interference with the visible light imaging element by unnecessary light suppression grooves provided in the infrared light separating prism.

4. 2. The light beam separating optical system according to claim 1, wherein the lens that is compatible with the lens mount is a C-mount lens that has little optical correction for the thickness of the glass inserted on the image side and has a short optical separating glass length on the image side.

5. 5. An optical device comprising any one of the light beam separating optical systems according to claim 1 to 4.

Images