JP2008250122A - Color separation optical system and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color separation optical system capable of improving color reproducibility by providing characteristics close to ideal spectroscopic characteristics. <P>SOLUTION: The color separation optical system 1 separates incident light L into four color light components of three color light components of blue color light LB, red color light LR and green color light LG and cyan color light LC. The cyan color light LC is a fourth color light component used for correction of color reproduction of the red color light LR. Imaging devices 4B, 4R, 4G, 4C for respective color lights such as CCD are arranged on positions corresponding to the respective color lights separated by the color separation optical system 1. The imaging device includes a calculation circuit 60 which calculates a signal value Rs' of red color corrected by a prescribed calculation, on the basis of the signal value Cs' obtained by the imaging device 4R for red color light and a signal light value Cs obtained by the imaging device 4C for cyan color light. Thereby, a negative sensitivity part of red color can be easily reproduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a color separation optical system that separates incident light into a plurality of color lights, and an imaging device that includes the color separation optical system.

  In general, an imaging apparatus such as a television camera or a video camera is provided with a color separation optical system. FIG. 13 shows a configuration example of a conventional color separation optical system. The color separation optical system 101 separates incident light L incident through the photographing lens 102 into three color light components of blue light LB, red light LR, and green light LG. Image pickup devices 4B, 4R, and 4G for each color light such as a CCD (Charge Coupled Device) are arranged at positions corresponding to the respective color lights separated by the color separation optical system 101. The color separation optical system 101 is called a Philips type color separation optical system, and in order from the light incident side along the optical axis Z1, the first prism 110, the second prism 120, and the third prism The first prism 110 extracts blue light LB, the second prism 120 extracts red light LR, and the third prism 130 extracts green light LG.

  A blue light reflecting dichroic film DB1 is formed on the reflection / transmission surface 111 of the first prism 110. On the reflection / transmission surface 121 of the second prism 120, a red light reflection dichroic film DR1 is formed. A trimming filter 151 is provided on the light exit surface of the first prism 110. A dichroic film 151 </ b> A is formed on the light exit surface of the trimming filter 151. Similarly, a trimming filter 152 formed with a dichroic film 152A is provided on the light exit surface of the second prism 120, and a trimming filter 153 formed with a dichroic film 153A is formed on the light exit surface of the third prism 130. Is provided. The trimming filters 151, 152, and 153 are provided to bring the spectral characteristics closer to the ideal characteristics, and spectral components of wavelength components that cannot be sufficiently shaped by the blue light reflecting dichroic film DB1 and the red light reflecting dichroic film DR1. Has the role of adjusting characteristics.

  FIG. 15 shows spectral characteristics that are generally ideal in a color imaging system for three colors of a red (R) component, a blue (B) component, and a green (G) component. The ideal characteristics shown in FIG. 15 are standardized so that the maximum value of each color light component is 1. This “ideal characteristic” is converted from the chromaticity coordinates of the three primary colors of the color reproduction medium, and can be obtained by primary conversion of the color matching function of the XYZ color system. Here, the “color reproduction medium” reproduces (displays) an image taken by the imaging device, and is a display device such as a liquid crystal monitor or a projector. FIG. 14 shows an example of chromaticity coordinates of the three primary colors R, G, and B for obtaining ideal characteristics. The three primary colors R, G, and B determine the color range that can be reproduced by the color reproduction medium.

  If the same characteristics as the ideal characteristics shown in FIG. 15 are obtained using the color separation optical system 101 shown in FIG. 13, ideal color reproduction can be performed. However, in practice, it is difficult to achieve the same characteristic as the ideal characteristic, and the design is such that the characteristic approximates the ideal characteristic. In the conventional color separation optical system 101, ideal characteristics are obtained by appropriately adjusting the dichroic films DB1 and DR1 formed on each prism and the dichroic films 151A, 152A, and 153A formed on the trimming filters 151, 152, and 153. It was designed to have approximate characteristics. FIG. 16 shows spectral transmission characteristics of a conventional general color separation optical system obtained by performing such a design.

  FIG. 17 shows a design example of the dichroic films DB1 and DR1 used in the conventional color separation optical system 101. As shown in FIG. 17, conventionally, as the dichroic films DB1 and DR1, the characteristic curve of the wavelength vs. transmittance shows a sharp rise or fall compared to the ideal characteristic curve shown in FIG. Something with was used. Further, unnecessary wavelength components of light emitted from the exit surface of each prism are blocked using trimming filters 151, 152, 153 provided with dichroic films 151A, 152A, 153A.

  As described above, conventionally, the characteristics are usually adjusted using various trimming filters. For example, Patent Document 1 proposes a method for improving the color reproduction by increasing the skin tone luminance level by using a trimming filter having special spectral transmission characteristics. In addition, instead of the dichroic film DR1, a half mirror is disposed on the joint surface between the second prism 120 and the third prism 130, and a dichroic film having transmission characteristics approximate to ideal characteristics is used as the trimming filters 152 and 153. A method of adjusting the transmission characteristics by applying such a method is known. FIG. 18 shows the spectral characteristics of a conventional color separation optical system approximated to ideal characteristics by performing such special adjustment.

  Here, the three-color separation optical system that includes three prisms and extracts three light components of red, blue, and green light has been described above. However, the color separation optical that includes four prisms and extracts four light components. The system is also known. For example, in paragraph [0007] of Patent Document 2, in a television camera, green light is divided into two, red, blue, first green light, and second green light are extracted, and two images for green are captured. It is described that the resolution is improved by shifting the pixel by a half pixel for green. Paragraph [0017] of Patent Document 2 describes that the prism surface is coated as a half mirror as a means for dividing green light into two. In addition, paragraph [0008] of Patent Document 2 describes that infrared light is obtained in addition to red, blue, and green light by a four-color separation optical system.

By the way, in the ideal characteristic shown in FIG. 15, there is a region where the negative spectral sensitivity is obtained, and in particular, there are many regions (region 100 in FIG. 15) where the red spectral property is negative. This negative region is theoretically obtained, and it is impossible to directly reproduce this negative portion with an actual optical system. Actually, the three-color separation optical system shown in FIG. 13 cannot reproduce the negative region as shown in FIG. Conventionally, a technique for obtaining a negative characteristic that cannot be directly reproduced by this optical system by calculation is known. For example, in Patent Document 3, in a color reader, a filter that separates white light in two directions using a half mirror and transmits light in a wavelength region corresponding to a red negative region (cyan light) in one optical path. Is arranged to take out cyan light, and a three-color splitting optical system is arranged in the other optical path to take out three colors of red, blue and green light. Then, by performing an operation of subtracting the cyan light output value from the normal red light output value, the negative red characteristic is reproduced. Further, Patent Document 4 discloses a color sensor configured to separate a plurality of color lights in the stacking direction by stacking a plurality of thin films such as organic dye thin films. This color sensor receives red, blue, green light, and cyan light and picks them up as an imaging signal by color separation using an organic dye thin film or the like instead of optical color separation.
JP-A-2005-208256 Japanese Patent No. 3507122 JP 59-230366 A JP 2005-269526 A

  However, in a conventional color separation optical system that uses a trimming filter with a dichroic film on the exit surface of the prism, the dichroic film has a wavelength range with high reflectivity as a characteristic of the dichroic film. There is a problem that multiple reflection occurs between the imaging surface and a ghost or flare, resulting in a deterioration in image quality. FIG. 19 shows, as an example, multiple reflection that occurs on the exit surface side of the third prism 130 that extracts the green light LG in the conventional color separation optical system 101. As illustrated in FIG. 19, the imaging element 4G includes an imaging surface 401G, a cover glass 402, and an extraction electrode 403. For example, part of the green light LG that has passed through the green trimming filter 153 is the imaging surface. The reflected light is reflected and reflected according to the wavelength selection characteristics of the dichroic film 153 A of the trimming filter 153. In this way, multiple reflected light 160 is generated, resulting in ghost / flare. For this reason, conventionally, it has been difficult to realize an imaging system having ideal spectral characteristics with reduced ghost and flare.

  In addition, in a light splitting optical system using a half mirror as described in Patent Document 3 in order to reproduce a negative region of ideal characteristics, each color light is extracted after the incident light is separated into two by the half mirror. There is a problem of inefficiency. For example, only cyan light is extracted from one optical path separated by a half mirror, and the other color light is wasted. Therefore, the use efficiency is halved compared to a normal three-color separation optical system. In addition, color separation using an organic dye thin film as described in Patent Document 4 has a problem that color separation is poor as compared with the case of using optical color separation means. If the four-color separation is performed by the color separation prism, it is thought that a color separation property and a good light utilization efficiency can be realized. However, conventionally, for improving the resolution as described in Patent Document 2, Although it has been proposed to divide one color light into two or use a four-color separation optical system for the purpose of obtaining infrared light, it reproduces the negative region and improves color reproducibility. For this purpose, a four-color separation optical system with high light efficiency and good color separation is not used.

  The present invention has been made in view of such problems, and a first object thereof is a color separation optical system capable of obtaining characteristics close to ideal spectral characteristics and improving color reproducibility, and An imaging device is provided. The second objective is to reduce the ghost and flare compared to the conventional wavelength selection method using a trimming filter with a dichroic film while improving the color reproducibility by obtaining characteristics close to ideal spectral characteristics. Another object of the present invention is to provide a color separation optical system and an image pickup apparatus that can be made to operate.

  The color separation optical system according to the present invention includes first to third prisms that extract blue light, red light, and green light contained in incident light as first to third color light components, and correction of color reproduction of red light. And a fourth prism for extracting a fourth color light component used in the above.

  In the color separation optical system according to the present invention, blue light, red light, and green light are extracted as the first to third color light components by the first to third prisms. In addition, the fourth color light component used for correcting the color reproduction of red light is extracted by the fourth prism. Since the four-color separation is performed by the color separation prism, the color separation property is good and the light utilization efficiency is good compared to the case where a half mirror is used. Then, by performing a predetermined calculation on the imaging device side using the imaging signal obtained from the fourth color light component, it is possible to satisfactorily reproduce a region having a negative sensitivity with respect to the red spectral characteristic.

  In the color separation optical system according to the present invention, for example, a first prism, a second prism, and a third prism are arranged in order from the light incident side, and the second prism and the third prism are arranged. A fourth prism is disposed between the first prism and the first prism as blue light, the second prism as red light as the second color light component, and the third prism as third color light component. A configuration in which green light is extracted and a portion of light in a wavelength region of 400 nm to 600 nm in the incident light is preferably extracted as the fourth color light component in the fourth prism.

  Further, the first prism has a first dichroic film that reflects blue light, and the reflected blue light is extracted as a first color light component. The second prism has a first dichroic film. The second dichroic film that reflects the red light that has passed through the light source, and the reflected red light is extracted as a second color light component. The fourth prism is transmitted through the first and second dichroic films. The third dichroic film that reflects part of the light in the wavelength region of 400 nm to 600 nm is extracted, and the reflected light is extracted as a fourth color light component. A configuration may be adopted in which green light transmitted through the second dichroic film and further transmitted through the third dichroic film is extracted as a third color light component.

  In such a configuration, blue light is reflected as the first color light component by the first dichroic film, and the blue light is extracted by the first prism. Further, the second dichroic film reflects red light as the second color light component, and the red light is extracted by the second prism. The third dichroic film reflects a part of light having a wavelength range of 400 nm to 600 nm transmitted through the first and second dichroic films as the fourth color light component, and the reflected light is the fourth color light component. Extracted as a color light component. Further, green light transmitted through the first, second and third dichroic films is extracted from the third prism as a third color light component. Since wavelength selection is performed by the dichroic film formed on each prism surface, characteristics close to ideal spectral characteristics can be obtained without using a trimming filter with a dichroic film on the exit surface of the prism. Since it is not necessary to use a trimming filter with a dichroic film, it is possible to suppress the occurrence of ghosts and flares conventionally caused by the dichroic film of the trimming filter. Thus, it is possible to realize an imaging system having ideal spectral characteristics with reduced ghost and flare.

  The color separation optical system according to the present invention may further include an absorptive filter disposed on the front side of the first prism or on the exit surface side of the prism that extracts red light and having characteristics approximating the visibility. good. Further, a coat type infrared cut filter that is disposed in front of the first prism and cuts infrared light may be further provided. Further, an ultraviolet cut filter that is disposed in front of the first prism and blocks ultraviolet light may be further provided. As a result, it becomes easier to obtain characteristics close to ideal spectral characteristics.

  Further, an antireflection film may be provided on the exit surface of at least one prism. This is advantageous in reducing ghost and flare.

An image pickup apparatus according to the present invention includes a color separation optical system according to the present invention and an image pickup element that is provided corresponding to each color light separated by the color separation optical system and outputs an electrical signal corresponding to each incident color light. It is provided.
In the imaging apparatus according to the present invention, an imaging signal with high color reproducibility can be obtained based on each color light obtained by the color separation optical system of the present invention.

The image pickup apparatus according to the present invention corrects the red signal corrected by the following equation based on the signal value obtained by the image sensor for red light and the signal value obtained by the image sensor for fourth color light. It is preferable to further include an arithmetic circuit for calculating the value Rs ′. However, Rs is a red signal value obtained by an image sensor for red light, Cs is a signal value obtained by an image sensor for fourth color light, and k is optimized to obtain an ideal red characteristic. Coefficient.
Rs ′ = Rs−kCs

  According to the color separation optical system of the present invention, blue light, red light, and green light are extracted as the first to third color light components by the first to third prisms, and the color of red light is extracted by the fourth prism. Since the fourth color light component used for correction of reproduction is extracted, compared to the case where four color components are obtained by using a half mirror or the like, a light separation efficiency and light utilization efficiency can be realized. . Then, by performing a predetermined calculation on the imaging apparatus side using the imaging signal obtained by the fourth color light component, the negative sensitivity region of the red spectral characteristic can be reproduced well, and the ideal spectral The characteristics close to the characteristics can be obtained and the color reproducibility can be improved.

  In particular, the blue light reflected by the first dichroic film is extracted from the first prism as the first color light component, and the red light reflected by the second dichroic film is used as the second color light component as the second prism. A part of the light in the wavelength region of 400 nm or more and 600 nm or less that is transmitted through the first and second dichroic films and reflected by the third dichroic film is extracted from the fourth prism as a fourth color light component, When green light that has passed through the first and second dichroic films and further passed through the third dichroic film is extracted as a third color light component, a trimming filter with a dichroic film is provided on the exit surface of the prism. It is possible to easily obtain characteristics close to ideal spectral characteristics without using them. This makes it possible to reduce ghosts and flares compared to the conventional wavelength selection method using a trimming filter with a dichroic film, and to improve the color reproducibility by obtaining characteristics close to ideal spectral characteristics. Can do.

  According to the image pickup apparatus of the present invention, since an image pickup signal corresponding to the color light obtained by the high-performance color separation optical system of the present invention is output, it is possible to perform image pickup with high color reproducibility. In particular, the corrected red signal value Rs ′ is calculated by a predetermined calculation based on the signal value obtained by the red light image sensor and the signal value obtained by the fourth color light image sensor. By doing so, the red negative sensitivity portion can be easily reproduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a main configuration of an imaging apparatus including a color separation optical system 1 according to an embodiment of the present invention. This imaging device is used as an imaging part of a television camera, for example. The color separation optical system 1 decomposes the incident light L incident through the taking lens 2 into four color light components of blue light LB, red light LR, and green light LG and four color light components of cyan light LC. It is. The cyan light LC is a fourth color light component used for correcting the color reproduction of the red light LR. Image pickup elements 4B, 4R, 4G, and 4C for each color light such as a CCD are arranged at positions corresponding to the respective color lights separated by the color separation optical system 1. This imaging device calculates a corrected red signal value Rs ′ based on the signal value Rs obtained by the red light imaging element 4R and the signal value Cs obtained by the cyan light imaging element 4C. An arithmetic circuit 60 is provided.

  The color separation optical system 1 is called a Philips type color separation optical system, and sequentially from the light incident side along the optical axis Z1, the IR (infrared) cut filter 3, the first prism 10, and the first Two prisms 20 and a third prism 30 are provided. The color separation optical system 1 further includes a fourth prism 40 disposed between the second prism 20 and the third prism 30. In the color separation optical system 1 in the present embodiment, the first prism 10 extracts blue light LB, the second prism 20 extracts red light LR, the third prism 30 extracts green light LG, and the fourth prism 40. This is a configuration example for extracting cyan light LC.

  The first prism 10 has a first surface 11, a second surface 12, and a third surface 13. The third surface 13 of the first prism 10 is a light exit surface. A trimming filter 51 is provided on the exit surface. The trimming filter 51 is not provided with a dichroic film for characteristic adjustment which has been conventionally used. Instead, an antireflection film 51AR for preventing ghost and flare is provided on the light emission surface of the trimming filter 51. Is formed. Note that the antireflection film 51AR may be formed directly on the third surface 13 of the first prism 10 without providing the trimming filter 51.

  A blue light reflecting dichroic film DB as a first dichroic film is formed on the second surface 12 of the first prism 10. The blue light reflecting dichroic film DB has a film configuration that reflects the blue light LB as the first color light component and transmits the red light LR and the green light LG. The blue light reflecting dichroic film DB is an ideal in which the slope of the transmission characteristic curve indicating the transmittance with respect to the wavelength is converted from the chromaticity coordinates of the three primary colors of the color reproduction medium and is determined based on the color matching function of the XYZ color system. It has a shape along the characteristic curve on the short wavelength side of the green spectral characteristic. The “ideal characteristic” here is a conventionally known characteristic as shown in FIG. 15, for example, converted from the chromaticity coordinates of the three primary colors of the color reproduction medium, and the color matching function of the XYZ color system. Can be obtained by a linear transformation. As the “ideal characteristic”, an ideal characteristic itself represented by a color matching function of the RGB color system may be used.

  FIG. 2A shows an example of a transmission characteristic curve of the blue light reflecting dichroic film DB in the configuration example of FIG. The blue light reflecting dichroic film DB has a transmission characteristic curve whose slope is in accordance with the characteristic curve on the short wavelength side of the ideal green spectral characteristic within a wavelength range of 430 nm to 670 nm. It is configured to have a shape that changes to rise. More specifically, the average slope value at which the transmission characteristic curve changes from 20% to 80% between the minimum transmittance and the maximum transmittance within a wavelength range of 430 nm to 670 nm is 0.2 (% / Nm) and 2.0 (% / nm) or less.

  The second prism 20 has a first surface 21, a second surface 22, and a third surface 23. The second prism 20 is disposed with a predetermined air interval 10AG with respect to the first prism 10. More specifically, the first surface 21 of the second prism 20 and the second surface 12 of the first prism 10 are arranged to face each other with an air gap 10AG so as to be substantially parallel. The third surface 23 of the second prism 20 is a light exit surface. A trimming filter 52 is provided on the exit surface. Similar to the trimming filter 51 in the first prism 10, the trimming filter 52 is not provided with a dichroic film for characteristic adjustment. Instead, the trimming filter 52 has a light exit surface for preventing ghost and flare. An antireflection film 52AR is formed. Note that the antireflection film 52AR may be formed directly on the third surface 23 of the second prism 20 without providing the trimming filter 52.

  A red light reflecting dichroic film DR as a second dichroic film is formed on the second surface 22 of the second prism 20. The red light reflecting dichroic film DR has a film configuration that reflects the red light LR as the second color light component and transmits the green light LG. The red light reflecting dichroic film DR has a shape in which the slope of the transmission characteristic curve indicating the transmittance with respect to the wavelength follows the characteristic curve on the long wavelength side of the ideal green spectral characteristic described above.

  FIG. 2B shows an example of a transmission characteristic curve of the red light reflecting dichroic film DR in the configuration example of FIG. The red light reflecting dichroic film DR has a transmission characteristic curve whose slope is in line with the characteristic curve on the long wavelength side of the ideal green spectral characteristic within a wavelength range of 430 nm to 670 nm. It is configured to have a shape that changes to fall. More specifically, the average slope value of the transmission characteristic curve that changes from 80% to 20% between the maximum transmittance and the minimum transmittance within the wavelength range of 430 nm to 670 nm is −2.0 ( % / Nm) to −0.2 (% / nm) or less.

  The fourth prism 40 has a first surface 41, a second surface 42, and a third surface 43. The fourth prism 40 is arranged with a predetermined air interval with respect to the second prism 20. More specifically, the second surface 20 of the second prism 20 and the first surface 41 of the fourth prism 40 are arranged to face each other with an air space therebetween so as to be substantially parallel. The third surface 43 of the fourth prism 40 is a light exit surface. A trimming filter 54 is provided on the exit surface. Similar to the trimming filter 51 in the first prism 10, the trimming filter 54 is not provided with a dichroic film for characteristic adjustment. Instead, the trimming filter 54 has a light exit surface for preventing ghost and flare. An antireflection film 53AR is formed. Note that the antireflection film 53AR may be formed directly on the third surface 43 of the fourth prism 40 without providing the trimming filter 54.

  A cyan light reflecting dichroic film DC as a third dichroic film is formed on the second surface 22 of the fourth prism 40. The cyan light reflecting dichroic film DC has a film configuration that reflects part of the light in the cyan color region of 400 nm or more and 600 nm or less as the fourth color light component and transmits the green light LG.

FIG. 3A shows characteristics of a specific design example of the blue light reflecting dichroic film DB, the red light reflecting dichroic film DR, and the cyan light reflecting dichroic film DC used in the color separation optical system 1. ing. Among the characteristics shown in FIG. 3A, the characteristics of the blue light reflecting dichroic film DB and the red light reflecting dichroic film DR are obtained by, for example, film design specifically shown as numerical data in FIGS. Further, the characteristics of the cyan light reflecting dichroic film DC can be obtained by, for example, film design specifically shown as numerical data in FIG. In FIG. 3B, “Sub-H4” represents a substance H4 (manufactured by Merck & Co., Germany) whose main component is LaTiO ₃ . However, the film material, the number of layers, and the film thickness of each layer are not limited to the examples shown in FIGS. 4, 5, and 3 (B).

  The third prism 30 has a first surface 31 and a second surface 32. The third prism 30 is configured to take out the green light LG that is transmitted through the blue light reflecting dichroic film DB and the red light reflecting dichroic film DR and further transmitted through the cyan light reflecting dichroic film DC. The third prism 30 is bonded to the fourth prism 40 via a cyan light reflecting dichroic film DC. More specifically, the second surface 42 of the fourth prism 40 and the first surface 31 of the third prism 30 are joined via a cyan light reflecting dichroic film DC. The second surface 32 of the third prism 30 is a light exit surface. A trimming filter 53 is provided on the exit surface. Similar to the trimming filter 51 in the first prism 10, the trimming filter 53 is not provided with a dichroic film for characteristic adjustment. Instead, the trimming filter 53 has a light exit surface for preventing ghost and flare. An antireflection film 53AR is formed. Note that the antireflection film 53AR may be formed directly on the second surface 32 of the third prism 30 without providing the trimming filter 53.

  The IR cut filter 3 is disposed on the front side of the first prism 10. The IR cut filter 3 is preferably composed of an absorptive filter having characteristics approximating to visual sensitivity in order to easily obtain characteristics close to ideal spectral characteristics. Further, when infrared light cannot be sufficiently removed only by the absorption filter, a coat type infrared cut filter that cuts infrared light may be further provided. FIG. 1 shows a configuration example in which a flat absorption filter is coated with a film 3R that cuts infrared light. Note that the IR cut filter 3 may be disposed not on the front side of the first prism 10 but on the light exit surface side of a prism (second prism 20 in FIG. 1) that extracts red light.

  Although not shown, the color separation optical system 1 may further include an absorption type or coat type ultraviolet cut filter that is disposed in front of the first prism 10 and cuts ultraviolet light.

  Next, the operation of the imaging apparatus in the present embodiment, particularly the optical operation and effect of the color separation optical system 1 will be described.

  In this imaging apparatus, subject light from a subject (not shown) irradiated by a light source (not shown) is incident on the color separation optical system 1 via the photographing lens 2. In the color separation optical system 1, the incident light L is decomposed into three color light components of blue light LB, red light LR, and green light LG and four color light components of cyan light LC. More specifically, first, the blue light LB of the incident light L is reflected by the blue light reflecting dichroic film DB and extracted from the first prism 10 as the first color light component. Further, the red light LR that has passed through the blue light reflecting dichroic film DB is reflected by the red light reflecting dichroic film DR and is extracted from the second prism 20 as the second color light component. Further, part of the light in the wavelength range of 400 nm to 600 nm transmitted through the blue light reflecting dichroic film DB and the red light reflecting dichroic film DR is reflected by the cyan light reflecting dichroic film DC, and the reflected light is the fourth light. Are extracted from the fourth prism 40 as the color light components. Further, the green light LG transmitted through the blue light reflecting dichroic film DB, the red light reflecting dichroic film DR, and the cyan light reflecting dichroic film DC is extracted from the third prism 30 as a third color light component. Each color light separated by the color separation optical system 1 is incident on the image pickup devices 4B, 4R, 4G, and 4C provided for the respective color lights. The image sensors 4B, 4R, 4G, and 4C output electrical signals corresponding to the incident color lights as image signals.

In this imaging apparatus, imaging with four color light components obtained by adding cyan light LC as the fourth color light component in addition to the blue light LB, the red light LR, and the green light LG, makes the imaging system more ideal. It can be close to the characteristics. In the ideal characteristics of the imaging system shown in FIG. 15, there are areas where the sensitivity is negative, and in particular, there are many areas where the red spectral characteristics are negative (area 100 in FIG. 15). This negative sensitivity region is difficult to reproduce by the usual three-color separation method. However, in the present embodiment, the negative sensitivity portion can be reproduced by the calculation in the calculation circuit 60 on the imaging device side by acquiring the cyan light LC corresponding to the negative sensitivity region as the color light component. It becomes possible. That is, the arithmetic circuit 60 performs an operation of appropriately optimizing the characteristic value obtained from the cyan light LC from the characteristic value obtained from the color-separated red light LR as in the following arithmetic expression. By doing so, it is possible to obtain a characteristic value that reproduces the negative sensitivity portion.
Rs ′ = Rs−kCs
However,
Rs: Red signal value obtained by the image sensor 4R for red light Cs: Signal value obtained by the image sensor 4C for cyan light k: Optimized to obtain an ideal red characteristic (negative sensitivity) Coefficient.

  In the present embodiment, the curve indicating the characteristic of the blue light reflecting dichroic film DB and the curve indicating the characteristic of the red light reflecting dichroic film DR have a shape along the characteristic curve of the ideal green spectral characteristic. Therefore, characteristics close to ideal spectral characteristics can be obtained without using a trimming filter with a dichroic film on the exit surface of the prism. Since it is not necessary to use a trimming filter with a dichroic film, it is possible to suppress the occurrence of ghosts and flares conventionally caused by the dichroic film of the trimming filter. Thus, it is possible to realize an imaging system having ideal spectral characteristics with reduced ghost and flare.

Hereinafter, the spectral characteristics obtained by this embodiment will be shown by actual design examples.
FIG. 6 shows an example of spectral characteristics of optical elements other than the prism portion in the imaging apparatus. In FIG. 6, as the characteristics of the optical elements other than the prism portion, a light source having a color temperature of 3200K, a photographing lens 2, an IR cut filter 3, and a CCD as the image sensors 4R, 4G, 4B, 4C are shown. Yes.

  FIG. 7 shows the spectral transmission characteristics of the entire prism portion (the first, second, third, and fourth prisms 10, 20, 30, 40) having the film design shown in FIG. . FIG. 8 shows a total spectral transmission characteristic of the entire optical system in the imaging apparatus, which combines the characteristics of the optical elements other than the prism part shown in FIG. 6 and the characteristics of the entire prism part shown in FIG. ing. 7 and 8, C indicates the spectral characteristic of the cyan light LC.

  FIG. 9 shows characteristics obtained by normalizing the overall spectral transmission characteristics shown in FIG. FIG. 9 also shows ideal characteristics (B0, R0, G0) for comparison. The ideal characteristic here is the characteristic shown in FIG. 15 which has been conventionally known. In FIG. 9, B1, R1, G1, and C1 indicate characteristics obtained directly in the design example according to the present embodiment. In FIG. 9, C1 indicates the spectral characteristics of the cyan light LC. “R1-2C1” is a characteristic corresponding to Rs ′ obtained by the above-described optimized calculation. It can be seen that the characteristic of “R1-2C1” obtained by the calculation reproduces the negative sensitivity and is closer to the red ideal characteristic (R0).

  FIG. 10 is a u′v ′ chromaticity diagram showing the color reproducibility in the design example according to the present embodiment in comparison with the prior art. The horizontal axis represents the u ′ chromaticity coordinate value, and the vertical axis represents the v ′ chromaticity coordinate value. In the figure, a triangular area surrounded by a broken line connects the chromaticity coordinate values of the three primary colors R, G, and B of the color reproduction medium (monitor), and indicates a color range that can be reproduced on the color reproduction medium. . The closer to the triangle, the higher the saturation. 10 is hidden because the chromaticity coordinates are enlarged, the primary red color R coordinate point of the color reproduction medium is present in the upper right direction, and the primary blue color B coordinate point is in the lower left direction. Existing. In the figure, the coordinate point of the white circle “◯” in the triangular area indicates the object white color. Also, in the figure, coordinate points indicated by black triangles “▲” in the triangular area represent coordinate points of an arbitrary color according to the conventional configuration. Coordinate points indicated by white squares “□” represent coordinate points of an arbitrary color in the design example according to the present embodiment. In the conventional configuration and the design example according to the present embodiment, the deviation amount from the ideal point (reproduction color deviation amount) is indicated by a solid line connecting the coordinate points. In the conventional configuration, the reproduced color has moved in the red area in the upper right, but the design example according to the present embodiment is greatly improved. In the design example according to the present embodiment, as a whole balance, there is no place where the color moves from the ideal point, and the color reproducibility is improved. In particular, the color reproducibility in cyan is improved. The average color difference for the seven colors B (blue), G (green), R (red), C (cyan), Y (yellow), M (magenta), and skin (skin color) is 8.84 to 5.96. Improved.

  FIG. 11 shows the amount of ghost generation in the color separation optical system 1 according to the present embodiment in comparison with the conventional configuration. Here, the conventional configuration is the case of the color separation optical system 101 including trimming filters 151, 152, 153 on which dichroic films 151A, 152A, 153A are formed, as shown in FIG. On the other hand, in the color separation optical system 1 according to the present embodiment, antireflection films 51AR and 52AR for preventing ghost and flare are provided on the light exit surfaces of the trimming filters 51, 52, 53, and 54 instead of the dichroic film. , 53AR, 54AR are formed.

  FIG. 11 shows, as an example, the amount of ghost generated on the side where the green light LG is emitted. In FIG. 11, a curve denoted by reference numeral 95 indicates the transmittance of the green light LG between the trimming filter 153 in the conventional configuration and the trimming filter 53 in the present embodiment. A curve denoted by reference numeral 91 indicates the reflectance of the dichroic film 153A of the trimming filter 153 in the conventional configuration. A curve denoted by reference numeral 92 indicates the reflectance of the antireflection film 53AR of the trimming filter 53 in the present embodiment. The amount of ghost of the green light LG in the conventional configuration is obtained by multiplying the transmittance indicated by reference numeral 95 and the reflectance indicated by reference numeral 91. A curve denoted by reference numeral 93 represents the conventional ghost generation amount. On the other hand, the ghost generation amount of the green light LG in the present embodiment is obtained by multiplying the transmittance indicated by reference numeral 95 and the reflectance indicated by reference numeral 92. A curve denoted by reference numeral 94 indicates the amount of ghost generated in this embodiment. Compared with the prior art, the amount of ghost generation is greatly reduced in the present embodiment. In addition, in FIG. 11, the example of the general antireflection coating which reduces reflection in the visible light whole region is shown as antireflection film 53AR. However, an antireflection coating in a specific wavelength range that reduces the reflectance particularly in the wavelength band emitted from the prism exit surface may be used.

  As described above, according to the color separation optical system 1 and the imaging apparatus according to the present embodiment, the four color light components including the fourth color light component are extracted by the four color separation optical system using the color separation prism, Since the fourth color light component is used for correcting the color reproduction of red light, compared with the case where four color components are obtained by using a half mirror or the like, the color light component has a better light utilization efficiency. realizable. Then, by performing a predetermined calculation on the imaging apparatus side using the imaging signal obtained by the fourth color light component, the negative sensitivity region of the red spectral characteristic can be reproduced well, and the ideal spectral The characteristics close to the characteristics can be obtained and the color reproducibility can be improved. Further, according to the color separation optical system 1 according to the present embodiment, ghosts and flares can be reduced as compared with the conventional wavelength selection method using a trimming filter with a dichroic film, and ideal spectral characteristics. It is possible to improve the color reproducibility by obtaining characteristics close to.

In particular, according to the imaging apparatus according to the present embodiment, since the imaging signal corresponding to the color light obtained by the color separation optical system 1 according to the present embodiment is output, imaging with high color reproducibility is performed. It can be carried out. In particular, the red signal value Rs ′ corrected by a predetermined calculation based on the signal value obtained by the image sensor 4R for red light and the signal value obtained by the image sensor 4C for fourth color light. By calculating, the red negative sensitivity part can be easily reproduced.
<Modification>

In addition, this invention is not limited to the said embodiment, A various deformation | transformation implementation is possible.
FIG. 12 shows a configuration of a color separation optical system 1-1 according to the modification. The color separation optical system 1-1 is different from the color separation optical system 1 in FIG. The color separation optical system 1-1 is configured to extract red light LR with the first prism 10 and blue light LB with the second prism 20. This modification differs from the color separation optical system 1 of FIG. 1 in that the prism surfaces forming the red light reflecting dichroic film DR and the blue light reflecting dichroic film DB are different, and the order of taking out the red light LR and the blue light LB is different. The basic configuration, operation, and effect are the same as those of the color separation optical system 1 shown in FIG.

  In the color separation optical system 1 of FIG. 1, the blue light reflecting dichroic film DB is formed as the first dichroic film on the second surface 12 of the first prism 10. In the optical system 1-1, a red light reflecting dichroic film DR is formed instead of the blue light reflecting dichroic film DB. The red light reflecting dichroic film DR has a film configuration that reflects the red light LR as the first color light component and transmits the blue light LB and the green light LG. The red light reflecting dichroic film DR in the present modification example is different only in the surface of the prism on which the film is formed, and the characteristic itself is different from that of the red light reflecting dichroic film DR in the color separation optical system 1 in FIG. It is the same. The transmission characteristic curve is the same as the transmission characteristic curve shown in FIG.

  Further, in the color separation optical system 1 of FIG. 1, the red light reflecting dichroic film DR is formed as the second dichroic film on the second surface 22 of the second prism 20. In the color separation optical system 1-1, a blue light reflecting dichroic film DB is formed as a second dichroic film instead of the red light reflecting dichroic film DR. The blue light reflecting dichroic film DB is configured to reflect the blue light LB as the second color light component and transmit the green light LG. The blue light reflecting dichroic film DB in this modification example is different only in the surface of the prism on which the film is formed, and the characteristic itself is different from that of the blue light reflecting dichroic film DB in the color separation optical system 1 in FIG. It is the same. The transmission characteristic curve is the same as the transmission characteristic curve shown in FIG.

  In the color separation optical system 1-1, first, the red light LR of the incident light L is reflected by the red light reflecting dichroic film DR and extracted from the first prism 10 as the first color light component. Further, the blue light LB transmitted through the red light reflecting dichroic film DR is reflected by the blue light reflecting dichroic film DB, and is extracted from the second prism 20 as the second color light component. The subsequent extraction of light by the fourth prism 40 and the third prism 30 is the same as that of the color separation optical system 1 of FIG.

It is sectional drawing which shows one structural example of the imaging device provided with the color separation optical system which concerns on one embodiment of this invention. It is explanatory drawing about the characteristic (A) of the blue light reflection dichroic film | membrane DB used with the color separation optical system shown in FIG. 1, and the characteristic (B) of the red light reflection dichroic film | membrane DR. FIG. 1 is a characteristic diagram showing a design example of a blue light reflecting dichroic film DB, a red light reflecting dichroic film DR, and a cyan light reflecting dichroic film DC used in the color separation optical system shown in FIG. 1, and a film of the cyan light reflecting dichroic film DC. It is a figure which shows an example of data. It is a figure which shows the numerical example of the film | membrane design of the blue light reflection dichroic film | membrane DB used with the color separation optical system shown in FIG. It is a figure which shows the numerical example of the film | membrane design of the red light reflection dichroic film | membrane DR used with the color separation optical system shown in FIG. It is a characteristic view which shows the spectral characteristic of optical elements other than the prism part in the imaging device which concerns on one embodiment of this invention. It is a characteristic view which shows the spectral characteristic of the prism part in the imaging device which concerns on one embodiment of this invention. It is a characteristic view which shows the comprehensive spectral characteristic of the optical system in the imaging device which concerns on one embodiment of this invention. It is the characteristic view which showed the standardized comprehensive spectral characteristic in one embodiment of this invention compared with the ideal characteristic. FIG. 5 is a u′v ′ chromaticity diagram showing color reproducibility in an embodiment of the present invention as compared with a conventional one. FIG. 6 is a characteristic diagram showing the amount of ghost generation in a color separation optical system according to an embodiment of the present invention in comparison with the conventional art. It is sectional drawing which shows the 1st modification of the imaging device provided with the color separation optical system which concerns on one embodiment of this invention. It is sectional drawing which shows the structural example of the conventional color separation optical system. It is an xy chromaticity diagram showing chromaticity coordinates of three primary colors for obtaining ideal characteristics. It is a characteristic view which shows the normalized ideal characteristic. It is a characteristic view which shows the spectral characteristic of the conventional general color separation optical system. It is a characteristic view which shows an example of the characteristic of the dichroic film | membrane used with the conventional color separation optical system. It is a characteristic view which shows the spectral characteristic approximated to the ideal characteristic in the conventional color separation optical system. It is explanatory drawing about the multiple reflection which arises in the conventional color separation optical system.

Explanation of symbols

  L ... incident light, LB ... blue light component, LR ... red light component, LG ... green light component, LC ... cyan light component, DB ... blue light reflecting dichroic film, DR ... red light reflecting dichroic film, DC ... cyan light reflecting Dichroic film, Rs ... red signal value, Cs ... cyan signal value, Rs' ... corrected red signal value, 1, 1-1 ... color separation optical system, 2 ... photographing lens, 3 ... IR cut filter, 4R, 4G 4B, 4C... Image sensor, 10... 1st prism, 20... 2nd prism, 30... 3rd prism, 40 ... 4th prism, 51. Filter, 53 ... third trimming filter, 54 ... fourth trimming filter, 51AR ... first antireflection film, 52AR ... second antireflection film, 53AR ... third antireflection film, 54A ... fourth antireflection film, 60 ... arithmetic circuit.

Claims (9)

First to third prisms for extracting blue light, red light, and green light contained in incident light as first to third color light components;
A color separation optical system, comprising: a fourth prism that extracts a fourth color light component used for correcting color reproduction of red light. In order from the light incident side, the first prism, the second prism, and the third prism are arranged, and the second prism and the third prism are arranged between the second prism and the third prism. 4 prisms are arranged,
The first prism extracts blue light as the first color light component, the second prism extracts red light as the second color light component, and the third prism extracts green light as the third color light component. And
2. The color separation according to claim 1, wherein the fourth prism is configured to extract a part of light having a wavelength range of 400 nm or more and 600 nm or less from incident light as the fourth color light component. Optical system. The first prism includes a first dichroic film that reflects blue light, and the reflected blue light is extracted as the first color light component.
The second prism has a second dichroic film that reflects the red light transmitted through the first dichroic film, and the reflected red light is extracted as the second color light component.
The fourth prism includes a third dichroic film that reflects a part of light having a wavelength range of 400 nm to 600 nm that is transmitted through the first and second dichroic films, and the reflected light is It is set as the structure taken out as a 4th color light component,
The third prism is configured to extract green light transmitted through the first and second dichroic films and further transmitted through the third dichroic film as the third color light component. The color separation optical system according to claim 2. 4. The apparatus according to claim 1, further comprising an absorptive filter disposed on the front side of the first prism or on the exit surface side of the prism for extracting red light and having characteristics approximating the visibility. 2. The color separation optical system according to item 1. The color separation optical according to any one of claims 1 to 3, further comprising a coat type infrared cut filter that is disposed in front of the first prism and cuts infrared light. system. The color separation optical system according to any one of claims 1 to 3, further comprising an ultraviolet cut filter that is disposed in front of the first prism and blocks ultraviolet light. The color separation optical system according to any one of claims 1 to 3, wherein an antireflection film is provided on an exit surface of at least one prism. A color separation optical system according to any one of claims 1 to 7,
An image pickup apparatus comprising: an image pickup device provided corresponding to each color light separated by the color separation optical system and outputting an electrical signal corresponding to each incident color light. Based on the signal value obtained by the red light image sensor and the signal value obtained by the fourth color light image sensor, the corrected red signal value Rs ′ is calculated by the following equation. The imaging apparatus according to claim 8, further comprising an arithmetic circuit.
Rs ′ = Rs−kCs
However,
Rs: red signal value obtained by the red light image sensor Cs: signal value obtained by the fourth color light image sensor k: coefficient optimized to obtain the ideal red characteristic .

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