JP2021044790A - Miniaturized luminous flux separation optical system and optical device - Google Patents

Abstract

To provide a miniaturized multi-plate industrial camera capable of using a wide variety of highly convenient single-plate C-mount compatible lenses in infrared and visible light separation optical systems.SOLUTION: A luminous flux separation optical system includes a lens mount, a separation 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, and a visible light imaging element that converts the visible light into a visible light image. The visible light imaging element is configured to shorten the length of an optical axis glass material of prism on the visible light side while maintaining the flange back in terms of air defined in the lens mount for the optical path length on the visible light side as much as possible without interfering with the other optical member, and increase the length of the air part to secure the flange back. There is also provided an optical device.SELECTED DRAWING: Figure 2

Description

The present invention relates to a light beam separation optical system used in an optical device such as a video camera, and is a two-plate or multi-plate camera that separates infrared light and visible light, which is particularly useful for medical cameras, surveillance cameras, image analysis / measurement cameras, and the like. In the present invention, the present invention relates to a light beam separation optical system that provides a miniaturized prism configuration.

In endoscopic cameras, dermascopes for skin observation, cameras for microscopes, etc., visible light and infrared light (including near-infrared light and mid-infrared light) for diagnosing and observing the condition of the epidermis and the affected area. It is necessary to separate and obtain the separated visible light image and infrared light image. It is used for observing many skin diseases by comparing and analyzing the appearance of the skin surface by the visible light image and the state of the inside near the epidermis by the infrared light image. It is difficult to distinguish these skin diseases from malignant tumors called melanoma and benign melanoma called melanocytic nevus only by observing the surface. Especially, internal inflammation and pigmentation are caused by hair cystitis, skin cancer, etc. This is because when it spreads more inward, it is necessary to observe the tissue structure inside the skin more accurately in order to distinguish the skin disease more accurately.

In addition, in security surveillance cameras, night-vision cameras, etc., infrared light is used to acquire trends in low-light environments such as night vision and night-vision environments as images, and infrared light images are used for monitoring and monitoring. It is carried out. These surveillance cameras acquire a visible light image for daytime images, and switch to acquire an infrared light image that enables image acquisition under low illuminance at night or under night vision. ..

Medical cameras and surveillance cameras that use infrared light and visible light as described above are required to be built into endoscopes and microscopes, and to be made smaller so that they are not noticed by the monitored person. Has been done. In this field, C-mount (industry standard) compatible lenses with a short back focus have been used in consideration of miniaturization, but most of these C-mount compatible lenses are premised on single-panel cameras. Therefore, it is suitable for use in multi-plate cameras such as 2-plate and 3-plate cameras that perform color separation using a prism or the like and take out multiple images with multiple imaging elements because of the influence of aberrations such as prisms. There wasn't.

In recent years, by reducing the image size of the image sensor and the size of the prism, C-mount is applied to multi-plate cameras that use prisms, and C-mount compatible lenses that have been glass-corrected in consideration of prism aberration have become available. Although they have been developed, these lenses have problems that they are limited in variety, expensive, and extremely inconvenient. In the present invention, for convenience, a medical camera, a surveillance camera, a military camera, etc. are referred to as an industrial camera, and a camera that acquires two or a plurality of images by two or a plurality of image sensors is referred to as a multi-plate camera. Although it is referred to, this does not limit its use.

There are many technologies for miniaturizing a multi-plate camera using a color separation prism by using a small lens with a short back focus and flange back. For example, in Patent Document 1, the color separation prism is miniaturized in order to use a small lens having a back focus of 20 mm or less, and the distance between the image sensor sensor and the prism exit surface is set to 1 mm or more to image scratches on the exit surface. A device for making it inconspicuous without picking it up with an element is disclosed. There are many examples of devising ways to use a lens with a short back focus or flange back, but the miniaturization itself is restricted by the size of the image sensor, the aperture of the lens, the physical size of the optical element, etc. It lacks convenience, such as specifying the lens to be used.

Further, Patent Document 2 discloses a color-separating prism configuration suitable for a C-mount lens having a short flange back length for use in an endoscope or the like. In Patent Document 2, a prism having a high refractive index is used to reduce the size, and a device for adapting to a C-mount lens is disclosed. However, such a high refractive index has a limit of increasing the refractive index. In addition, a lens suitable for such a C-mount is an expensive lens that has been glass-corrected for the purpose of being used for a prism, and a C-mount lens is also specified, which poses a problem in terms of cost.

Therefore, there has been a demand for a miniaturized prism configuration in which a C-mount lens for a single plate, which is not glass-corrected for a prism and can be obtained at a relatively low price, can be used without restrictions in a multi-plate industrial camera. In other words, in a multi-plate industrial camera that acquires multiple images with a prism or the like, a wide variety of lenses can be used if a lens suitable for a single-plate C mount that is not substantially glass-corrected becomes available. Therefore, a cheaper and more convenient industrial camera system can be constructed.

Jitsufuku 07-22641 Gazette JP-A-2017-205492

Therefore, the problem to be solved by the present invention is to provide a compact multi-plate industrial camera that enables the use of a wide variety of highly convenient single-plate C-mount compatible lenses in infrared and visible light separation optical systems. The purpose.

Further, a further problem to be solved by the present invention is that in a luminous flux decomposition optical system that decomposes into luminous flux of infrared light and visible light, it is desired to reduce the size of an endoscope, a surveillance camera, etc. by a smaller prism configuration. An object of the present invention is to provide a luminous flux separation optical system suitable for a multi-plate industrial camera.

Further, in the present invention, the dimensions of the camera lens and the image sensor are not limited as much as possible, and the camera lens and the image sensor can be freely selected, and the smaller configuration is suitable for an endoscope, a surveillance camera, and the like. It is an object of the present invention to provide a light beam separation optical system and an optical device using them.

In order to solve such a problem and achieve the above object, the present invention has a lens mount, a separation prism that separates incident light into infrared light and visible light, and the infrared light, as described in claim 1. In a light beam separation optical system having an infrared light imaging element that converts light into an infrared light image and a visible light imaging element that converts visible light into a visible light image, the optical path length on the visible light side is the lens mount. While maintaining the flange back in terms of air specified in the above, the length of the optical axis glass material of the prism on the visible light side is shortened as much as possible within the range where the visible light imaging element does not interfere with other optical members. It is characterized in that the length of the air portion is increased in order to secure the flange back.

Further, as described in claim 2, in the luminous flux separation optical system according to claim 1, the optical path length on the infrared light side has a longer optical path length than that on the visible light side. It is a feature.

Further, as described in claim 3, the present invention prevents the visible light imaging element from interfering with the unnecessary light suppression groove provided in the separation prism in the light beam separation optical system according to claim 1. The feature is that the length of the prism glass material on the visible light side is shortened.

Further, as described in claim 4, in the luminous flux separation optical system according to any one of claims 1 to 3, the lens mount is a C mount having a flange back of 17.526 mm. It is a feature.

Further, as described in claim 5, in the light beam separation optical system according to claim 4, the lens compatible with the lens mount is a C mount compatible lens without glass correction.

Further, the present invention is characterized in that it is an optical device provided with the luminous flux separation optical system according to any one of claims 1 to 5. The means for solving the above problems can be used in combination as much as possible.

In the light beam separation optical system of the present invention, the length of the prism having a refractive index greater than 1 on the optical path is shortened as much as possible within the range where the prism on the visible light side does not interfere with the member on the infrared light side, and the flange back air equivalent length is shortened. The rest of the air is made up of air. Since the prism portion is considerably shortened, the influence of aberration is significantly reduced even if a C-mount lens for a single plate without glass correction is used, and actual use becomes possible.

The wide variety of single-plate C-mount lenses currently on the market are C-mount lenses that are not glass-corrected because they do not require the use of prisms. By using these lenses, a wide variety of inexpensive lenses can be used. It can be replaced. Further, since the prism optical path length on the visible light side having a refractive index larger than 1 is shortened and the flange back length is secured by extending the air having a refractive index of 1 for the remaining optical path length, the light beam separation optical system It is possible to reduce the size. In the present invention, since the prism portion on the visible light side is simply shortened, it is not necessary to use an expensive prism with a high refractive index (high index), and the luminous flux separation optical system does not increase the burden of member cost. Miniaturization can be achieved.

Further, the light beam separation optical system in the present invention utilizes an unnecessary light suppression groove such as a ghost cut provided in the separation prism so that the image pickup element on the visible light side does not interfere with the infrared light separation prism or the like. Since the length of the glass material can be shortened, the prism part is further shortened, and even if a C-mount lens for a single plate without glass correction is used, it is possible to configure the structure so that aberration does not affect it more. An inexpensive light beam separation optical system can be configured, and a convenient and compact optical device such as an industrial camera can be provided. Further, a larger image sensor or the like can be used without intentionally downsizing the image sensor on the visible light side, and the degree of freedom in selecting the image sensor is not limited.

It is a schematic explanatory drawing of the light flux separation optical system by the conventional general-purpose separation prism. It is a schematic explanatory drawing of the light flux separation optical system which concerns on Example 1 of this invention. It is a schematic explanatory drawing of the light flux separation optical system which concerns on Example 2 of this invention.

The present invention will be described with reference to the drawings. All of the drawings described in the following examples are drawn as schematic schematic views for the purpose of explaining the present invention, and the actual dimensions and shapes are not particularly limited. Further, the dimensions, materials, shapes, relative arrangements, etc. of the components are not intended to limit the technical scope of the invention to those alone unless otherwise specified.

FIG. 1 is a schematic explanatory view showing an example of an infrared light and visible light separation optical system using a conventional separation prism. 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 an infrared light image and a visible light image is shown. Various interchangeable lenses are interchangeable by the interchangeable lens mount 1, and the luminous flux collected from the lens is incident on the infrared / visible light separation prism 2. The light beam incident on the prism 2 is reflected by the separation surface 3 at the wavelength R of the infrared light band and totally reflected by the reflection surface 4 of the prism 2, and infrared light imaging provided in parallel with the emission surface via the emission surface 5. It is incident on the element 6 and outputs an infrared light image as an electric signal.

The infrared / visible light separation surface 3 is formed of a dielectric multilayer film or a metal thin film, reflects infrared light (including near-infrared light and mid-infrared light), and transmits visible light. For the separation wavelength of such a separation prism, infrared light having a wavelength of 600 to 700 nm or more is extracted as reflected light depending on the purpose of use, and the wavelength in the visible light region is transmitted.

The transmitted light (visible light) T transmitted through the separation surface 3 is incident on the prism 7 arranged in the subsequent stage of the separation prism 2, and is visible light provided in parallel with the emission surface via the emission surface 8 of the prism 7. It enters the image pickup element 9 and outputs a visible light image as an electric signal. The output visible light image may be a black-and-white image or a color image depending on the purpose of use. In such a prism configuration, various filters are inserted in the optical path, and various filters are also inserted on the exit side of each prism to suppress unnecessary light such as correction of output characteristics and reflection prevention. To.

In such a prism configuration, the flange back optical path length (La + Lb) (air equivalent) between the flange back reference surface A and the image sensor surface B of infrared light and visible light is defined by each lens mount, and is compact. The C mount, which is called a lens mount, is defined as 17.526 mm. This flange back length is the optical path length in terms of air, and when a member having 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 depends on the thickness and refractive index of the member. Change.

Since the refractive index of the insertion member in the optical path such as glass or prism is larger than 1, the optical path length becomes longer than the air-equivalent optical path length. Therefore, for the purpose of miniaturization, a prism of a high refractive index (high index) type is used. In a general-purpose prism as shown in FIG. 1, a light beam enters the prism, emits light, and is almost composed of prism members up to an image sensor, and a member having a refractive index of about 1.5 to 1.8 is generally used. Is used. In the conventional two-plate prism configuration, each image sensor is arranged on the emission side of the infrared light and visible light prisms via a trimming filter and other filters according to the purpose of use. Usually, a C-mount compatible lens with glass correction is used in a multi-plate industrial camera in which light flux is separated by such a prism to acquire a plurality of captured images in order to reduce the influence of aberration caused by the prism.

FIG. 2 is a schematic explanatory view of a two-plate luminous flux separation optical system for separating infrared light and visible light according to the first embodiment of the present invention. Various interchangeable lenses 10 are interchangeable by the interchangeable lens mount 11, and the luminous flux collected from the lens 10 is incident on the infrared and visible light separation prism 12. The light beam incident on the prism 12 is reflected by the separation surface 13 at a wavelength in the infrared light band, and is totally reflected by the reflecting surface 14 of the prism 12 as reflected light R, and is provided parallel to the emitting surface via the emitting surface 15. It is incident on the infrared light image pickup device 16 and outputs an infrared light image as an electric signal.

Further, the transmitted light (visible light) T transmitted through the separation surface 13 is incident on the prism 17 arranged after the separation prism 12, and is parallel to the emission surface of the prism 17 through the emission surface 18 and the air gap 19. It is incident on the visible light imaging element 20 provided in the above, and outputs a color or black and white visible light image as an electric signal. Here, the prism 17 on the visible light side has an optical path length shorter than that of the conventional prism length Lb in FIG. 1 to Lb', and the lens interchangeable mount is formed by adjusting the air gap 19 (optical path length Lc) accordingly. The flange back length of 11 is maintained.

In the embodiment of FIG. 2, the visible light side prisms 17 are shortened as close as possible to each other within a range that does not interfere with the separation prism 12, and are adjusted by the air gap 19 to secure the flange back length. Here, since the flange back length is in terms of air, the prism (or glass) portion having a refractive index larger than the refractive index 1 in air (strictly speaking, vacuum) is shortened, and the air gap portion having a refractive index 1 is shortened. By extending, the actual size (La + Lb'+ Lc) between the flange back reference surface A and the image sensor reference surface B shown in FIG. 2 becomes the actual size between the flange back reference surface A and the image sensor reference surface B shown in FIG. It is shortened as compared with (La + Lb).

The shortening ratio of this prism portion varies depending on the infrared light separation prism, the C-mount lens standard, and the dimensions of the image sensor, but in the example of the general prism member available, the prism portion having the conventional configuration is about 30% to 40%. Can be shortened to. With such a configuration, the prism length on the visible light side is shortened to the extent that a single-plate C-mount lens without glass correction can be used, and a wide variety of single-plate industrial C-mount lenses are used at low cost. However, it is possible to construct an optical system to which aberration does not become a problem.

Here, the single-plate C-mount lens 10 conforming to the present invention is an industrial C-mount compatible lens generally used in a commercially available single-plate camera, which is generally referred to as no glass correction or no prism correction. Such a lens is a lens for a single plate (for one image pickup element) that does not require multiple color separations by a prism or the like, and therefore does not require glass correction for the prism. Is.

On the other hand, the optical path length on the infrared light side can be shortened as long as it does not interfere with members such as prisms and imaging elements on the visible light side, but infrared light has a longer wavelength than visible light and is greatly affected by the focal distance, and is red. Since the focus itself is almost out of focus due to the influence of chromatic aberration on the external light path, shortening the prism length is not given priority. That is, in the present invention, the optical path length on the visible light side and the optical path length on the infrared light side are configured differently, and priority is given to shortening the prism length on the visible light side as much as possible, and infrared light is used. By shortening so that the prism member and the member on the visible light side do not interfere with each other, it is shortened so that a commercially available C-mount lens for a single plate that is not substantially glass-corrected can be used. Therefore, in the prism configuration example of the present invention, it can be said that the optical path length on the infrared light side is longer than that on the visible light side.

Further, in the first embodiment, as shown in FIG. 2, the prism on the visible light side is shortened as much as possible to the infrared separation prism side, and the flange back length is secured by extending the air gap. However, by slightly extending the distance from the flange back reference surface A to the front surface of the prism, it is possible to shorten the air gap 19 by that amount. With such a prism configuration, the optical path length on the visible light side is further shortened, and the luminous flux separation prism configuration itself can be further miniaturized.

In this way, the prism transmission portion on the visible light side is significantly shortened, so that an interchangeable lens for a single plate that is compatible with the C mount and has not been subjected to glass correction can be used. By making such an interchangeable lens usable, not only can a wide variety of uses be possible in industrial cameras, but also cost reduction can be achieved. Further, by preferentially shortening the prism portion on the visible light side and securing the flange back length by an air gap, the length on the visible light side can be shortened and miniaturization becomes possible. In this method, not only the shortening is possible but also the cost can be reduced as compared with the case of simply using a high index prism.

FIG. 3 is a schematic explanatory view of a two-plate luminous flux separation optical system for separating infrared light and visible light according to the second embodiment of the present invention. The same reference numerals are given to the portions corresponding to the luminous flux separation optical system in FIG. In the second embodiment, the unnecessary light suppression groove 30 provided in the infrared light separation prism 12 is used to further shorten the prism configuration.

As for the light flux incident on the infrared separation prism 12, infrared light is reflected as reflected light R by the infrared light separation surface 13, and visible light is transmitted as transmitted light T. The transmitted visible light T is incident on the visible light imaging element 20 via the visible light prism 17 provided after the infrared light separation prism.

Here, the visible light image sensor 20 is installed directly with the visible light prism 17 without passing through the air gap 19 shown in FIG. 2, or through a desired filter 31 such as a trimming filter. When the air gap 19 is omitted or significantly shortened, and the visible light prism 17 is shortened, the image sensor 20 interferes with the infrared separation prism 12, but in the second embodiment, the unnecessary light suppression groove 30 is provided. It is provided so that the image sensor 20 can be inserted.

The unnecessary light suppression groove 30 is mainly intended for infrared ghost cutting, and an example of cutting the ghost light indicated by the dotted line G by the unnecessary light suppression groove 30 is shown. The unnecessary light suppression groove 30 forms a groove so that the ghost reflected light does not enter the image pickup device at a place that does not affect the optical path in the infrared light separation prism 12. Various shapes of this type of unnecessary light suppression groove 30 are considered, but the visible light image sensor 20 provided with the trimming filter 31 sandwiched in a state where the prism 17 on the visible light side is shortened as much as possible is infrared. A V-shaped notch is provided so as not to collide with the optical prism 12.

It is desirable that the visible light image sensor 20 can be used in an industrial camera from a full size to a small size image sensor depending on the purpose. By forming the unnecessary light suppression groove 30 of the infrared light prism 17 as described above, the size of the image sensor 20 is less limited even if the prism 17 on the visible light side is shortened, and the image sensor Increases the degree of freedom of choice.

As described above, according to the present invention, the prism portion on the visible light side is shortened, so that the camera is a multi-plate camera using a prism, but is relatively compatible with a wide variety of C mounts that are not glass-corrected. Since an inexpensive interchangeable lens can be used and the prism configuration of infrared light and visible light separation type can be miniaturized, the range of use and application in various industrial cameras is expanded, and the convenience is enhanced.

In the present invention, an example using a two-plate separation prism that separates infrared light and visible light by using a C-mount lens has been described, but the camera using the optical system of the present invention extracts infrared light. It can be widely applied to multi-plate video cameras for surveillance, microscopes, telescopes, military use, still image cameras, and mounts other than C-mount lenses. Not limited to the range disclosed in the above examples, a plurality of components can be appropriately combined within the claims, and can be widely applied to equipment using a luminous flux separation optical system, which is of great industrial usefulness. And have availability.

10 Interchangeable lens 11 Camera mount 12 Infrared light separation prism 13 Infrared light separation surface (separation film)
14 Infrared light reflecting surface 16 Infrared light imaging element 17 Visible light prism 19 Air gap 20 Visible light imaging element 30 Unnecessary light suppression groove 31 Filter

Claims (6)

A lens mount, a separation 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, and visible light that converts the visible light into a visible light image. In a light beam separation optical system having an optical image pickup element, the optical path length on the visible light side is the optical axis glass of the prism on the visible light side while maintaining the flange back in terms of air defined in the lens mount. The feature is that the length of the material is shortened as much as possible within the range where the visible light imaging element does not interfere with other optical members, and the length of the air portion is increased in order to secure the flange back. Light beam separation optical system. The luminous flux separation optical system according to claim 1, wherein the optical path length on the infrared light side has a longer optical path length than the visible light side. The first aspect of the present invention is that the length of the prism glass material on the visible light side is shortened so as to prevent the visible light imaging element from interfering with the unnecessary light suppression groove provided in the separation prism. Alternatively, the light flux separation optical system according to 2. The luminous flux separation optical system according to any one of claims 1 to 3, wherein the lens mount is a C mount having a flange back of 17.526 mm. The luminous flux separation optical system according to claim 4, wherein the lens compatible with the lens mount is a C mount compatible lens that has not been subjected to glass correction. An optical device provided with any of the luminous flux separation optical systems according to claims 1 to 5.

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