JP5075715B2 - Color separation optical system and imaging apparatus - Google Patents

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. 20 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. In the first prism 110 and the second prism 120, the surface 111 of the first prism 110 on which the blue light reflecting dichroic film DB1 is formed and the light incident surface of the second prism 120 are separated from each other by an air gap 110AG. It arrange | positions so that it may mutually oppose. 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. 22 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. Note that the ideal characteristics of FIG. 22 are normalized so that the maximum value of each color light component is 1, and the vertical axis indicates the transmittance intensity. 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. 21 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 characteristic as the ideal characteristic shown in FIG. 22 is obtained using the color separation optical system 101 shown in FIG. 20, 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. 23 shows spectral transmission characteristics of a conventional general color separation optical system obtained by performing such a design.

  FIG. 24 shows a design example of the dichroic films DB1 and DR1 used in the conventional color separation optical system 101. As shown in FIG. 24, 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. 25 shows spectral characteristics of a conventional color separation optical system approximated to ideal characteristics by performing such special adjustment.
JP-A-2005-208256

  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. 26 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 shown in FIG. 26, the imaging element 4G includes an imaging surface 401G, a cover glass 402, and an extraction electrode 403. For example, a part of the green light LG that has passed through the green trimming filter 153 is captured on the imaging surface 401G. The reflected light is reflected according to the wavelength selection characteristics of the dichroic film 153A of the trimming filter 153. In this way, multiple reflected light 160 is generated, resulting in ghost and flare. For this reason, conventionally, it has been difficult to realize an imaging system having ideal spectral characteristics with reduced ghost and flare.

  By the way, in the ideal characteristic shown in FIG. 22, there is a region where the negative spectral sensitivity is obtained, and in particular, there are many regions (region 100 in FIG. 22) 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. In the conventional color separation optical system, the negative region cannot be reproduced as shown in FIG. On the other hand, it is conceivable that negative characteristics that cannot be directly reproduced by the optical system are reproduced by calculation of signal processing on the imaging apparatus side. For example, a reversible conversion characteristic that eliminates the negative region is obtained with respect to the ideal characteristic shown in FIG. 22, and the conversion characteristic is an ideal characteristic that is reproduced by the color separation optical system. Then, by performing inverse transformation on the output from the color separation optical system by signal processing on the imaging device side, the negative region can be reproduced, and the original ideal characteristics can be reproduced in a pseudo manner. In designing a color separation optical system optimized for such conversion characteristics, it is preferable to obtain characteristics with a well-balanced color balance for each color so that the transmittance of a specific color component does not decrease.

  The present invention has been made in view of such a problem, and an object of the present invention is to reduce ghost and flare as compared with a conventional wavelength selection method using a trimming filter with a dichroic film, and for each color light. An object of the present invention is to provide a color separation optical system and an image pickup apparatus that are capable of improving the color reproducibility by obtaining characteristics close to ideal spectral characteristics in a well-balanced state.

  A color separation optical system according to a first aspect of the present invention is a color separation optical system that decomposes incident light into at least three color light components of blue light, red light, and green light, sequentially from the light incident side. A first prism that has a first dichroic film and extracts a first color light component reflected by the first dichroic film; and a second dichroic film that passes through the first dichroic film and passes through the first dichroic film. A second prism for extracting the second color light component reflected by the second dichroic film, and a third prism for extracting the third color light component transmitted through the first and second dichroic films. The first dichroic film has a film configuration that reflects green light as the first color light component, and the second dichroic film has a film configuration that reflects blue light as the second color light component. The slope of the reflection characteristic curve indicating the reflectance with respect to the wavelength of the first dichroic film has a shape along the characteristic curve on the short wavelength side and long wavelength side of the ideal green spectral characteristic, and the second dichroic film The slope of the transmission characteristic curve indicating the transmittance with respect to the wavelength has a shape along the characteristic curve on the short wavelength side of the ideal red spectral characteristic. Furthermore, the film configuration is such that the maximum reflectance is 36% or more within the wavelength range of 500 nm to 570 nm in the reflection characteristic curve of the first dichroic film.

In the color separation optical system according to the first aspect of the present invention, the first dichroic film has a film configuration that reflects green light as the first color light component, and the first prism extracts green light. The second dichroic film has a film configuration that reflects blue light as the second color light component, and blue light is extracted by the second prism. From the third prism, a third color light component (color light different from the first color light component and the second color light component) transmitted through the first and second dichroic films is extracted. In this case, the trimming filter with the dichroic film is used on the exit surface of the prism because the curve indicating the characteristic of the first dichroic film has a shape that follows the characteristic curve of the ideal green spectral characteristic. Therefore, characteristics close to ideal spectral characteristics can be obtained. 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.
Further, in this color separation optical system, the reflection characteristic curve of the first dichroic film is configured to have a predetermined reflectance value within a predetermined wavelength range in consideration of the balance of spectral characteristics of each color. As a result, in the final color light extraction stage, only a specific color light is not significantly attenuated, and a state in which the color balance is in order is obtained. As a result, the efficiency of extracting green light extracted by the first prism is improved, and each color light is in a state where the color balance is in order.

  A color separation optical system according to a second aspect of the present invention is a color separation optical system that decomposes incident light into at least three color light components of blue light, red light, and green light, and sequentially from the light incident side. A first prism that has a first dichroic film and extracts a first color light component reflected by the first dichroic film; and a second dichroic film that passes through the first dichroic film and passes through the first dichroic film. A second prism for extracting the second color light component reflected by the second dichroic film, and a third prism for extracting the third color light component transmitted through the first and second dichroic films. The first dichroic film has a film configuration that reflects green light as the first color light component, and the second dichroic film has a film configuration that reflects red light as the second color light component. The slope of the reflection characteristic curve indicating the reflectance with respect to the wavelength of the first dichroic film has a shape along the characteristic curve on the short wavelength side and long wavelength side of the ideal green spectral characteristic, and the second dichroic film The slope of the reflection characteristic curve indicating the reflectance with respect to the wavelength has a shape along the characteristic curve on the short wavelength side of the ideal red spectral characteristic. Furthermore, the film configuration is such that the maximum reflectance is 36% or more within the wavelength range of 500 nm to 570 nm in the reflection characteristic curve of the first dichroic film.

In the color separation optical system according to the second aspect of the present invention, the first dichroic film has a film configuration that reflects green light as the first color light component, and the first prism extracts green light. The second dichroic film has a film configuration that reflects red light as the second color light component, and the second prism extracts red light. From the third prism, a third color light component (color light different from the first color light component and the second color light component) transmitted through the first and second dichroic films is extracted. In this case, the trimming filter with the dichroic film is used on the exit surface of the prism because the curve indicating the characteristic of the first dichroic film has a shape that follows the characteristic curve of the ideal green spectral characteristic. Therefore, characteristics close to ideal spectral characteristics can be obtained. 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.
Further, in this color separation optical system, the reflection characteristic curve of the first dichroic film is configured to have a predetermined reflectance value within a predetermined wavelength range in consideration of the balance of spectral characteristics of each color. As a result, in the final color light extraction stage, only a specific color light is not significantly attenuated, and a state in which the color balance is in order is obtained. As a result, the efficiency of extracting green light extracted by the first prism is improved, and each color light is in a state where the color balance is in order.

  In the color separation optical system according to the first or second aspect of the present invention, in the portion where the slope of the reflection characteristic curve of the first dichroic film rises within the wavelength range of 430 nm to 670 nm, an ideal green spectrum It has a shape that changes from a low reflectance to a high reflectance along the characteristic curve on the short wavelength side of the characteristic, and in the portion that falls within the wavelength range of 430 nm to 670 nm, the ideal green spectral characteristic It is preferable to have a shape that changes from a high reflectance to a low reflectance along the characteristic curve on the long wavelength side.

In the color separation optical system according to the first or second aspect of the present invention, the color separation optical system is disposed on at least one of the front side of the first prism or the exit surface side of the prism that extracts red light, and approximates the visibility. An absorptive filter having the above may be further provided. 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. Moreover, you may further provide the depolarizing plate which arrange | positions ahead of the 1st prism and cancels the polarization | polarized-light in the specific direction of incident light.
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.

Here, in the color separation optical system according to the first or second aspect of the present invention, “ideal spectral characteristics” are “target predetermined spectral characteristics”. For example, it is a characteristic obtained by performing reverse conversion so as to further reduce a negative value with respect to the ideal characteristic indicated by the color matching function of the RGB color system.
Or, conversion that can be inversely converted to reduce the negative value with respect to the ideal characteristics converted from the chromaticity coordinates of the three primary colors of the color reproduction medium and indicated by the primary conversion of the color matching function of the XYZ color system. The applied characteristics may be used.

  In the color separation optical system according to the third aspect of the present invention, the slope of the reflection characteristic curve indicating the reflectance with respect to the wavelength of the first dichroic film in the color separation optical system according to the first aspect of the present invention is ideal. The shape of the transmission characteristic curve, which has substantially the same shape as the characteristic curve on the short wavelength side and the long wavelength side of the green spectral characteristic, and the transmittance characteristic curve showing the transmittance with respect to the wavelength of the second dichroic film is ideal red spectral characteristic It has a shape substantially equal to the characteristic curve on the short wavelength side.

  In the color separation optical system according to the fourth aspect of the present invention, the slope of the reflection characteristic curve indicating the reflectance with respect to the wavelength of the first dichroic film in the color separation optical system according to the second aspect of the present invention is ideal. The shape of the reflection characteristic curve showing the reflectance with respect to the wavelength of the second dichroic film is substantially equal to the characteristic curve on the short wavelength side and the long wavelength side of the green spectral characteristic, and the ideal red spectral characteristic It has a shape substantially equal to the characteristic curve on the short wavelength side.

  Here, in the color separation optical system according to the third or fourth aspect of the present invention, the “shape substantially equal to the ideal characteristic curve of spectral characteristics” is, for example, a standardized predetermined ideal characteristic curve. The shape is preferably such that the slope of the characteristic curve falls within ± 10% of the slope.

An image pickup apparatus according to the present invention includes a color separation optical system according to any one of the first to fourth aspects of the present invention, which is optimized with the characteristics subjected to the conversion that can be inversely converted as an ideal characteristic, and the color separation. An image sensor that is provided corresponding to each color light decomposed by the optical system and outputs an electrical signal corresponding to each incident color light, and a negative value in the ideal characteristics based on the signal value obtained by the image sensor And an arithmetic circuit for performing inverse transformation to reproduce.
In the image pickup apparatus according to the present invention, an image pickup signal with high color reproducibility can be obtained based on each color light obtained in a state in which the color balance is adjusted by the color separation optical system of the present invention.

  According to the color separation optical system according to any one of the first to fourth aspects of the present invention, the curve indicating the characteristic of the first dichroic film has a shape along the characteristic curve of the ideal green spectral characteristic or Since the configuration has substantially the same shape, 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. 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. In addition, since the dichroic film is configured so that the reflection characteristic curve of the first dichroic film has a predetermined reflectance within a predetermined wavelength range in consideration of the balance of spectral characteristics of each color, the color balance of each color light is adjusted. Ideal spectral characteristics can be obtained in a well-organized state.

  According to the imaging apparatus of the present invention, since the imaging signal corresponding to the color light obtained by the high-performance color separation optical system of the present invention is output, the color reproducibility is high and each color light is spectrally separated. Imaging with a good balance of characteristics can be performed. In particular, the color separation optical system is optimized with the characteristics subjected to reverse conversion that reduces negative values as ideal characteristics, and the ideal characteristics are determined based on the signal values obtained through the color separation optical system. Since an operation for performing an inverse transformation to reproduce a negative value is performed, a portion having negative spectral sensitivity that cannot be directly obtained by the color separation optical system can be reproduced in a pseudo manner.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[First Embodiment]

  FIG. 1 shows a main configuration of an imaging apparatus including a color separation optical system 1 according to the first 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 separates the incident light L incident through the photographing lens 2 into three color light components of blue light LB, red light LR, and green light LG. Image pickup elements 4B, 4R, and 4G 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 apparatus performs an inverse transformation that reproduces a negative value in an ideal characteristic, as will be described later, based on the signal values Rs, Gs, and Bs of each color output from the imaging elements 4B, 4R, and 4G. 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 in the present embodiment is a configuration example in which the first prism 10 extracts green light LG, the second prism 20 extracts blue light LB, and the third prism 30 extracts red light LR.

  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 green light reflecting dichroic film DG as a first dichroic film is formed on the second surface 12 of the first prism 10. The green light reflecting dichroic film DG has a film configuration that reflects the green light LG as the first color light component and transmits the blue light LB and the red light LR. As will be described later, the green light reflecting dichroic film DG is designed with a film characteristic corresponding to a desired predetermined spectral characteristic.

  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 blue light reflecting dichroic film DB as a second dichroic film is formed on the second surface 22 of the second prism 20. The blue light reflecting dichroic film DB is configured to reflect the blue light LB as the second color light component and transmit the red light LR. As will be described later, the blue light reflecting dichroic film DB is designed with film characteristics corresponding to a predetermined predetermined spectral characteristic.

  The third prism 30 has a first surface 31 and a second surface 32. The third prism 30 is bonded to the second prism 20 via the blue light reflecting dichroic film DB. More specifically, the second surface 22 of the second prism 20 and the first surface 31 of the third prism 30 are joined via the blue light reflecting dichroic film DB. 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. The “absorptive filter having characteristics approximating the visibility” referred to here is called a “visibility correction filter” and is a transmission that approximates the sensitivity characteristics of the human eye and attenuates from the green to the red wavelength. This is an absorptive filter that has a low transmittance and a low transmittance even in the infrared region. 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 the prism (the third prism 30 in FIG. 1) that extracts red light. Further, the IR cut filter 3 may be disposed on both the front side of the first prism 10 and the light exit surface side of the prism that extracts red light. 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. However, in the case where the IR cut filter 3 is arranged on the light exit surface side of the prism that extracts red light, it is preferable that the IR cut coat is not applied and only the absorption filter is used. In that case, it is more preferable that the absorption filter is provided with an antireflection film.

  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.

  Here, ideal characteristics to be optically reproduced by the color separation optical system 1 in the present embodiment will be described.

  In the present embodiment, the characteristic that is finally desired to be reproduced as the output of the imaging device is an ideal characteristic as shown in FIG. This is not standardized and is substantially the same as the general ideal characteristic shown in FIG. This ideal characteristic is, for example, converted from the chromaticity coordinates of the three primary colors of the color reproduction medium, and is indicated by the primary conversion of the color matching function of the XYZ color system. Or the ideal characteristic itself shown by the color matching function of RGB color system may be sufficient. Although such an ideal characteristic has a region having a negative spectral sensitivity, the region having the negative spectral sensitivity cannot be optically directly reproduced by the color separation optical system 1. Therefore, in the present embodiment, a characteristic obtained by performing reversible conversion so as to eliminate the negative region with respect to the ideal characteristic shown in FIG. 2A is obtained in advance, and the conversion characteristic is obtained by the color separation optical system. 1 is the ideal characteristic (target predetermined spectral characteristic) to be reproduced. The output from the color separation optical system 1 (the signal values Rs, Gs, Bs of the respective colors output from the image sensors 4B, 4R, 4G) is reversed by the signal processing circuit (arithmetic circuit 60) on the imaging device side. By performing an operation that performs conversion, the negative region is reproduced, and the original ideal characteristics are reproduced in a pseudo manner.

FIG. 2B performs a reversible conversion that eliminates the negative region described above on the ideal characteristics R (x), G (x), and B (x) of each color shown in FIG. An example of the conversion characteristics R ′ (x), G ′ (x), and B ′ (x) is shown. Such conversion can be performed by the calculation of primary conversion as shown in the following [Equation 1]. M is a matrix that minimizes negative values as much as possible for the conversion characteristics R ′ (x), G ′ (x), and B ′ (x). Here, R ′ (x), G ′ (x), and B ′ (x) are multiplied by the inverse matrix M ⁻¹ to perform inverse transformation, so that the original ideal characteristics R (x), G (x), B A characteristic approximate to (x) can be obtained.

In the present embodiment, the film characteristics of the green light reflecting dichroic film DG and the blue light reflecting dichroic film DB are the conversion characteristics R ′ (x), G ′ (x), and B ′ (x) as ideal characteristics. The design is such that characteristics approximate to the conversion characteristics R ′ (x), G ′ (x), and B ′ (x) are obtained. Here, since the conversion characteristics R ′ (x), G ′ (x), and B ′ (x) are such characteristics that negative values are minimized, theoretically, the color separation optical system 1 Can be directly reproduced optically. Thereafter, the characteristics approximated to the original ideal characteristics R (x), G (x), and B (x) can be obtained by multiplying the inverse matrix M ⁻¹ by the calculation in the calculation circuit 60 on the imaging apparatus side. it can. As a result, it is possible to reproduce a portion that is virtually a negative region.

  3A and 3B show an example of the reflection characteristic curve of the green light reflecting dichroic film DG in the present embodiment. In the green light reflecting dichroic film DG, the inclination of the reflection characteristic curve indicating the reflectance with respect to the wavelength is the short wavelength side and the long wavelength of the ideal green spectral characteristic (the conversion characteristic G ′ (x) subjected to the primary conversion described above). It has a shape along the side characteristic curve. Specifically, the green light reflecting dichroic film DG has an ideal green color as shown in FIG. 3A in the portion where the slope of the reflection characteristic curve rises within the wavelength range of 430 nm to 670 nm. It is configured to have a shape that changes from a low reflectance to a high reflectance along a characteristic curve on the short wavelength side of the spectral characteristics. More specifically, the average slope value at which the reflection characteristic curve changes from 20% to 80% of the range between the lowest reflectance and the highest reflectance within a wavelength range of 430 nm to 670 nm is 0.2%. It is preferable to have a shape of (% / nm) or more and 2.0 (% / nm) or less.

  As shown in FIG. 3B, the green light reflecting dichroic film DG follows the characteristic curve on the long wavelength side of the ideal green spectral characteristic at the portion falling within the wavelength range of 430 nm to 670 nm. It has a shape that changes from high reflectivity to low reflectivity. More specifically, the average slope value at which the reflection characteristic curve changes from 80% to 20% of the range between the highest reflectance and the lowest reflectance within the wavelength range of 430 nm to 670 nm is −2. It preferably has a shape of 0 (% / nm) or more and -0.2 (% / nm) or less.

  In addition, the blue light reflecting dichroic film DB has a slope of the transmission characteristic curve indicating the transmittance with respect to the wavelength on the short wavelength side of the ideal red spectral characteristic (the above-described primary-converted conversion characteristic R ′ (x)). It is comprised so that it may have a shape along a characteristic curve.

In the present embodiment, the green light reflecting dichroic film DG has a shape in which the slope of the reflection characteristic curve indicating the reflectance with respect to the wavelength is substantially equal to the characteristic curve on the short wavelength side and the long wavelength side of the ideal green spectral characteristic. You may have. The blue light reflecting dichroic film DB may have a shape in which the slope of the transmission characteristic curve indicating the transmittance with respect to the wavelength is substantially equal to the characteristic curve on the short wavelength side of the ideal red spectral characteristic.
Here, the “shape substantially equal to the characteristic curve of the ideal spectral characteristic” is, for example, a conversion characteristic curve such as that shown in FIG. The shape is preferably such that the slope of the characteristic curve falls within ± 10% of the slope.

As described above, the green light reflecting dichroic film DG and the blue light reflecting dichroic film DB in the present embodiment are designed such that the slopes of the characteristic curves correspond to the ideal spectral characteristics. Further, in the present embodiment, the green light reflecting dichroic film DG is designed so that the reflection characteristic curve has the characteristics shown in FIG. That is, the reflection characteristic curve of the green light reflecting dichroic film DG is designed such that the maximum reflectance P is within the predetermined range Wt within the predetermined wavelength range Wλ.
Here, the wavelength range Wλ is, for example, a range from 500 nm to 570 nm.
Further, the range Wt of the maximum value P of the reflectance is a range of 36% or more (100% or less).

  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. More specifically, first, the green light LG of the incident light L is reflected by the green light reflecting dichroic film DG and extracted from the first prism 10 as the first color light component. Further, the blue light LB transmitted through the green light reflecting dichroic film DG is reflected by the blue light reflecting dichroic film DB, and is extracted from the second prism 20 as the second color light component. Further, the red light LR that has passed through the green light reflecting dichroic film DG and the blue light reflecting dichroic film DB is extracted from the third prism 30 as a third color light component. Each color light separated by the color separation optical system 1 enters the image pickup devices 4B, 4R, 4G provided corresponding to each color light. The imaging elements 4B, 4R, and 4G output an electrical signal corresponding to each incident color light as an imaging signal.

  In the present embodiment, the curve indicating the characteristic of the green light reflecting dichroic film DG has a shape along the characteristic curve of the ideal green spectral characteristic, and the curve indicating the transmission characteristic of the blue light reflecting dichroic film DB is By having a shape along the characteristic curve on the short wavelength side of the ideal red spectral characteristic, the characteristic close to the ideal spectral characteristic can be obtained without using a trimming filter with a dichroic film on the exit surface of the prism. can get. 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.

  Further, in the present embodiment, the color separation optical system 1 has the reflection characteristic curve of the green light reflecting dichroic film DG having a predetermined maximum value P within the predetermined wavelength range Wλ in consideration of the balance of the spectral characteristics of each color. Since each dichroic film is configured as described above, only a specific color light is not extremely attenuated at the final color light extraction stage, and a state in which the color balance is adjusted is obtained.

  The advantage of setting the reflectance of the green light reflecting dichroic film DG within the predetermined wavelength range Wλ to the predetermined maximum value range Wt will be described more specifically with reference to FIGS. 5 (A) and 5 (B). To do. In the color separation optical system 1, the component reflected by the green light reflecting dichroic film DG is extracted from the first prism 10 as green light LG. Therefore, for example, as shown in FIG. 5A, when the maximum reflectance P of the green light reflecting dichroic film DG is extremely low outside the predetermined range Wt, the ratio of light extracted as green light LG However, it becomes relatively less with respect to other color lights. On the other hand, as shown in FIG. 5B, if the maximum value P of the reflectance is within a predetermined range Wt, it is possible to balance with other color lights. Thereby, in particular, the extraction efficiency of the green light LG extracted by the first prism 10 is improved, and each color light is in a state in which the color balance is adjusted.

Hereinafter, the spectral characteristics obtained by this embodiment will be shown by actual design examples.
FIG. 6 shows characteristics in a specific design example of the green light reflecting dichroic film DG and the blue light reflecting dichroic film DB used in the color separation optical system 1. The characteristics shown in FIG. 6 can be obtained by, for example, the film design specifically shown as numerical data in FIGS. However, the film material, the number of layers, and the film thickness of each layer are not limited to the examples of FIGS. FIG. 9 shows the spectral transmission characteristics of the entire prism portion (the first, second, and third prisms 10, 20, and 30) on which the film design shown in FIG. 6 is applied.

  FIG. 10 shows an example of spectral characteristics of optical elements other than the prism portion in the imaging apparatus. In FIG. 10, 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, and 4B are shown. FIG. 11 shows the overall spectral transmission characteristics of the entire optical system in the imaging apparatus, which combines the characteristics of optical elements other than the prism section shown in FIG. 10 and the characteristics of the entire prism section shown in FIG. ing.

  FIG. 12 shows an inverse transformation characteristic (B1) obtained by performing an inverse transformation (see FIGS. 2A and 2B) for reproducing the negative value described above on the output from the color separation optical system 1. , R1, G1). FIG. 12 also shows ideal characteristics (B0, R0, G0) for comparison. Note that the ideal characteristic referred to here is a desired ideal characteristic (see FIG. 2A) that is finally desired to be reproduced as the imaging apparatus. Thus, according to the present embodiment, the negative sensitivity portion can be virtually reproduced finally, and a characteristic close to the ideal characteristic is obtained.

  FIG. 13 is a u′v ′ chromaticity diagram showing the color reproducibility in the design example according to the present embodiment in comparison with the case where a conventional general color separation optical system is used. 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. 13 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. The average color difference of the seven colors B (blue), G (green), R (red), C (cyan), Y (yellow), M (magenta), and skin (skin color) is about 8.9 to about 6. Improved to 9.

  FIG. 14 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 the trimming filters 151, 152, 153 on which the dichroic films 151A, 152A, 153A are formed as shown in FIG. In contrast, in the color separation optical system 1 according to the present embodiment, the anti-reflection films 51AR, 52AR, and 53AR for preventing ghost and flare are provided on the light exit surfaces of the trimming filters 51, 52, and 53 instead of the dichroic film. Is formed.

  FIG. 14 shows, as an example, the amount of ghost generated on the side where the green light LG is emitted. In FIG. 14, 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. Note that FIG. 9 shows an example of a general antireflection coating that reduces reflection in the entire visible light region as the 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 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 ideally. It is possible to improve the color reproducibility by obtaining a characteristic close to a typical spectral characteristic. In addition, since the dichroic film is configured so that the reflection characteristic curve of the first dichroic film has a predetermined reflectance within a predetermined wavelength range in consideration of the balance of spectral characteristics of each color, the color balance of each color light is adjusted. Ideal spectral characteristics can be obtained in a well-organized state.

Further, according to the imaging apparatus according to the present embodiment, since the imaging signal corresponding to the color light obtained by the high-performance color separation optical system 1 according to the present embodiment is output, color reproducibility is improved. It is possible to perform imaging with a high balance of spectral characteristics for each color light. In particular, the color separation optical system 1 is optimized with the characteristics subjected to reverse conversion that reduces negative values as ideal characteristics, and the ideal is based on the signal values obtained through the color separation optical system 1. Since the operation for performing the inverse transformation to reproduce the negative value in the characteristic is performed, the portion having the negative spectral sensitivity that cannot be directly obtained by the color separation optical system 1 can be reproduced in a pseudo manner.
[Second Embodiment]

  Next, a second embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the component substantially the same as the said 1st Embodiment, and description is abbreviate | omitted suitably.

  FIG. 15 shows the configuration of a color separation optical system 1-1 according to the second embodiment of the present invention. 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 green light LG by the first prism 10, red light LR by the second prism 20, and blue light LB by the third prism 30.

  In the color separation optical system 1-1 according to the present embodiment, the second surface 12 of the first prism 10 has a green light reflecting dichroic as a first dichroic film, as in the color separation optical system 1 of FIG. A film DG is formed. The characteristics of the reflection characteristic curve of the green light reflecting dichroic film DG in the present embodiment are the same as those in FIGS.

  In the color separation optical system 1 of FIG. 1, the blue light reflecting dichroic film DB is formed as the second dichroic film on the second surface 22 of the second prism 20, but the color according to the present embodiment. In the decomposition optical system 1-1, a red light reflecting dichroic film DR is formed as a second dichroic film 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 second color light component and transmits the blue light LB. The red light reflecting dichroic film DR has a characteristic curve on the short wavelength side of an ideal red spectral characteristic (the above-mentioned primary-converted conversion characteristic R ′ (x)) with an inclination of the reflection characteristic curve indicating the reflectance with respect to the wavelength. It is comprised so that it may have a shape along.

In the present embodiment, the red light reflecting dichroic film DR has a shape in which the slope of the reflection characteristic curve indicating the reflectance with respect to the wavelength is substantially equal to the characteristic curve on the short wavelength side of the ideal red spectral characteristic. Also good.
Here, the “shape substantially equal to the characteristic curve of the ideal spectral characteristic” is, for example, a conversion characteristic curve such as that shown in FIG. The shape is preferably such that the slope of the characteristic curve falls within ± 10% of the slope.

  In the color separation optical system 1-1, first, the green light LG of the incident light L is reflected by the green light reflecting dichroic film DG and extracted from the first prism 10 as the first color light component. The red light LR that has passed through the green light reflecting dichroic film DG 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, the blue light LB transmitted through the green light reflecting dichroic film DG and the red light reflecting dichroic film DR is extracted from the third prism 30 as a third color light component.

In the present embodiment, the green light reflecting dichroic film DG and the red light reflecting dichroic film DR are designed such that the slopes of their characteristic curves correspond to the ideal spectral characteristics. Furthermore, in the present embodiment, the green light reflecting dichroic film DG is designed so that the reflection characteristic curve has the characteristics shown in FIG. That is, the reflection characteristic curve of the green light reflecting dichroic film DG is designed such that the maximum reflectance P is within the predetermined range Wt within the predetermined wavelength range Wλ.
Here, the wavelength range Wλ is, for example, a range from 500 nm to 570 nm.
Further, the range Wt of the maximum value P of the reflectance is a range of 36% or more (100% or less).

  FIG. 17 shows characteristics in a specific design example of the green light reflecting dichroic film DG and the red light reflecting dichroic film DR in the present embodiment.

  In the present embodiment, the curve indicating the characteristic of the green light reflecting dichroic film DG has a shape along the characteristic curve of the ideal green spectral characteristic, and the curve indicating the reflecting characteristic of the red light reflecting dichroic film DR is: By having a shape along the characteristic curve on the short wavelength side of the ideal red spectral characteristic, the characteristic close to the ideal spectral characteristic can be obtained without using a trimming filter with a dichroic film on the exit surface of the prism. can get. 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.

In the present embodiment, each dichroic film is configured such that the reflection characteristic curve of the green light reflecting dichroic film DG has a predetermined reflectance within a predetermined wavelength range Wλ in consideration of the balance of spectral characteristics of each color. As a result, in the final color light extraction stage, only a specific color light is not significantly attenuated, and a state in which the color balance is arranged is obtained. In particular, the extraction efficiency of the green light LG extracted by the first prism 10 is improved, and each color light can be in a state in which the color balance is adjusted. Other configurations, operations, and effects are the same as those of the color separation optical system 1 of FIG.
[Third Embodiment]

  Next, a third embodiment of the present invention will be described. Note that components that are substantially the same as those in the first or second embodiment are denoted by the same reference numerals, and description thereof is omitted as appropriate.

  FIG. 18 shows a configuration of a color separation optical system 1-2 according to the fifth embodiment of the present invention. The color separation optical system 1-4 further includes a depolarization plate 55 disposed in front of the first prism 10 with respect to the color separation optical system 1 shown in FIG. Other configurations are the same as those of the color separation optical system 1 shown in FIG. The depolarization plate 55 is for depolarizing incident light in a specific direction.

  FIG. 19 shows an example of the spectral transmission characteristics for each polarization component in the entire prism portion (the entire first, second and third prisms 10, 20, and 30) when the depolarization plate 55 is not provided. Yes. For example, when the incident light component is biased toward a specific linearly polarized light component, the spectral characteristics change as compared to the case where the incident light is in a non-polarized state. FIG. 19 shows the characteristics when linearly polarized light components (P-polarized light and S-polarized light) orthogonal to each other are incident as incident light. The characteristic when the incident light is non-polarized light is shown as (P + S) / 2. In the present embodiment, since the depolarization plate 55 is disposed in front of the first prism 10, the polarization of incident light in a specific direction is eliminated, and is indicated by (P + S) / 2 in FIG. Such stable spectral characteristics can be obtained.

Similarly to the configuration examples in the other embodiments, the depolarization plate 55 may be provided in front of the first prism 10.
[Other embodiments]

The present invention is not limited to the above embodiments, and other modifications can be made.
For example, in each of the above-described embodiments, an example in which three prisms are provided as a color separation optical system and the light is separated into three color lights has been shown. However, the present invention includes four or more prisms and is provided with four or more color lights. The present invention can also be applied to a color separation optical system that decomposes.

It is a block diagram which shows an example of the imaging device provided with the color separation optical system which concerns on the 1st Embodiment of this invention. It is explanatory drawing about the ideal characteristic applied with the color separation optical system which concerns on the 1st Embodiment of this invention, (A) shows the ideal characteristic before primary conversion, (B) is after primary conversion. Shows ideal characteristics. It is explanatory drawing about the short wavelength side characteristic (A) of the green light reflection dichroic film | membrane DG in the color separation optical system which concerns on the 1st Embodiment of this invention, and the long wavelength side characteristic (B). It is explanatory drawing about the reflection characteristic curve of the green light reflection dichroic film | membrane DG in the color separation optical system which concerns on the 1st Embodiment of this invention. It is explanatory drawing about the effect of setting it as the characteristic shown in FIG. It is a characteristic view showing a design example of the green light reflecting dichroic film DG and the blue light reflecting dichroic film DB in the color separation optical system according to the first embodiment of the present invention. It is a figure which shows the numerical example of the film | membrane design of the green light reflection dichroic film | membrane DG in the color separation optical system which concerns on the 1st Embodiment of this invention. It is a figure which shows the numerical example of the film | membrane design of the blue light reflection dichroic film | membrane DB in the color separation optical system which concerns on the 1st 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 the 1st Embodiment of this invention. It is a characteristic view which shows the spectral characteristics of optical elements other than the prism part in the imaging device which concerns on the 1st 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 the 1st Embodiment of this invention. FIG. 6 is a characteristic diagram illustrating an inverse conversion characteristic obtained by performing an inverse primary conversion on the overall spectral characteristic in the imaging apparatus according to the first embodiment of the present invention in comparison with an ideal characteristic before the primary conversion. FIG. 6 is a u′v ′ chromaticity diagram showing color reproducibility in the imaging apparatus according to the first embodiment of the present invention in comparison with the conventional art. FIG. 5 is a characteristic diagram showing the amount of ghost generation in the color separation optical system according to the first embodiment of the present invention compared to the conventional art. It is a block diagram which shows an example of the imaging device provided with the color separation optical system which concerns on the 2nd Embodiment of this invention. It is explanatory drawing about the reflection characteristic curve of the green light reflection dichroic film | membrane DG in the color separation optical system which concerns on the 2nd Embodiment of this invention. It is a characteristic view showing a design example of the green light reflecting dichroic film DG and the red light reflecting dichroic film DR in the color separation optical system according to the second embodiment of the present invention. It is a block diagram which shows an example of the imaging device provided with the color separation optical system which concerns on the 3rd Embodiment of this invention. FIG. 6 is a characteristic diagram illustrating spectral characteristics of a prism portion in a color separation optical system considering a polarization component. 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, DB ... blue light reflecting dichroic film, DR ... red light reflecting dichroic film, DG ... green light reflecting dichroic film, 1,1 -1, 1-2 ... color separation optical system, 2 ... photographing lens, 3 ... IR cut filter, 4R, 4G, 4B ... imaging element, 10 ... first prism, 20 ... second prism, 30 ... third 51 ... first trimming filter, 52 ... second trimming filter, 53 ... third trimming filter, 51AR ... first antireflection film, 52AR ... second antireflection film, 53AR ... third Antireflection film, 55... Depolarization plate.

Claims (12)

A color separation optical system that decomposes incident light into at least three color light components of blue light, red light, and green light,
In order from the light incident side,
A first prism that has a first dichroic film and extracts a first color light component reflected by the first dichroic film;
A second prism that has a second dichroic film and extracts a second color light component transmitted through the first dichroic film and reflected by the second dichroic film;
A third prism for extracting a third color light component transmitted through the first and second dichroic films,
The first dichroic film has a film configuration that reflects green light as the first color light component, and the second dichroic film has a film configuration that reflects blue light as the second color light component. And
The slope of the reflection characteristic curve indicating the reflectance with respect to the wavelength of the first dichroic film is converted from the color matching function of the RGB color system or the chromaticity coordinates of the three primary colors of the color reproduction medium, and the like of the XYZ color system, etc. It changes from a low reflectance to a high reflectance within the wavelength range of 430 nm to 670 nm so as to follow the characteristic curve on the short wavelength side of the ideal green spectral characteristic indicated by the primary conversion of the color function. The average slope value is 0.2 (% / nm) or more and 2.0 (% / nm) or less in the portion where the range between the maximum reflectance and 20% changes to 80%, and the characteristics on the long wavelength side. Along the curve, it changes from high reflectance to low reflectance within the wavelength range of 430 nm or more and 670 nm or less, and the average slope in the portion that changes from 20% to 80% of the range between the lowest reflectance and the highest reflectance. The value is −2.0 (% / nm) or more and −0. And having a shape of 2 (% / nm) or less ,
The slope of the transmission characteristic curve indicating the transmittance with respect to the wavelength of the second dichroic film is converted from the color matching function of the RGB color system or the chromaticity coordinates of the three primary colors of the color reproduction medium, and the like of the XYZ color system, etc. It changes from low transmittance to high transmittance within the wavelength range of 430 nm or more and 670 nm or less along the characteristic curve on the short wavelength side of the ideal red spectral characteristic shown by the primary conversion of the color function. The portion where the average slope value is 0.2 (% / nm) or more and 2.0 (% / nm) or less in a portion that changes from 20% to 80% of the range between the maximum transmittance ,
And,
A color separation optical system characterized in that the maximum reflectance value is 36% or more within a wavelength range of 500 nm or more and 570 nm or less in the reflection characteristic curve of the first dichroic film. . A color separation optical system that decomposes incident light into at least three color light components of blue light, red light, and green light,
In order from the light incident side,
A first prism that has a first dichroic film and extracts a first color light component reflected by the first dichroic film;
A second prism that has a second dichroic film and extracts a second color light component transmitted through the first dichroic film and reflected by the second dichroic film;
A third prism for extracting a third color light component transmitted through the first and second dichroic films,
The first dichroic film has a film configuration that reflects green light as the first color light component, and the second dichroic film has a film configuration that reflects red light as the second color light component. And
The slope of the reflection characteristic curve indicating the reflectance with respect to the wavelength of the first dichroic film is converted from the color matching function of the RGB color system or the chromaticity coordinates of the three primary colors of the color reproduction medium, and the like of the XYZ color system, etc. It changes from a low reflectance to a high reflectance within the wavelength range of 430 nm to 670 nm so as to follow the characteristic curve on the short wavelength side of the ideal green spectral characteristic indicated by the primary conversion of the color function. The average slope value is 0.2 (% / nm) or more and 2.0 (% / nm) or less in the portion where the range between the maximum reflectance and 20% changes to 80%, and the characteristics on the long wavelength side. Along the curve, it changes from high reflectance to low reflectance within the wavelength range of 430 nm or more and 670 nm or less, and the average slope in the portion that changes from 20% to 80% of the range between the lowest reflectance and the highest reflectance. The value is −2.0 (% / nm) or more and −0. And having a shape of 2 (% / nm) or less ,
The slope of the reflection characteristic curve indicating the reflectance with respect to the wavelength of the second dichroic film is converted from the color matching function of the RGB color system or the chromaticity coordinates of the three primary colors of the color reproduction medium, and the like of the XYZ color system, etc. It changes from a low reflectance to a high reflectance within a wavelength range of 430 nm or more and 670 nm or less so as to follow the characteristic curve on the short wavelength side of the ideal red spectral characteristic shown by the primary conversion of the color function. An average slope value that changes from 20% to 80% of the range between the maximum reflectance and a shape that is 0.2 (% / nm) to 2.0 (% / nm) ,
And,
A color separation optical system characterized in that the maximum reflectance value is 36% or more within a wavelength range of 500 nm or more and 570 nm or less in the reflection characteristic curve of the first dichroic film. . The ideal spectral characteristic is a characteristic obtained by performing a primary conversion capable of reverse conversion, further reducing negative values, with respect to the ideal characteristic indicated by the color matching function of the RGB color system.
The color separation optical system according to claim 1, wherein the color separation optical system is a color separation optical system. The ideal spectral characteristic is converted from the chromaticity coordinates of the three primary colors of the color reproduction medium, and further reduces the negative value with respect to the ideal characteristic indicated by the primary conversion of the color matching function of the XYZ color system. It is a characteristic with possible first order transformation
The color separation optical system according to claim 1, wherein the color separation optical system is a color separation optical system. An absorptive filter is further provided that is disposed on at least one of the front side of the first prism or the exit surface side of the prism that extracts red light and has a characteristic that approximates the visibility.
The color separation optical system according to claim 1, wherein the color separation optical system is a color separation optical system. A coat type infrared cut filter that is disposed in front of the first prism and cuts infrared light is further provided.
The color separation optical system according to claim 1, wherein the color separation optical system is a color separation optical system. An ultraviolet cut filter that is disposed in front of the first prism and blocks ultraviolet light is further provided.
The color separation optical system according to claim 1, wherein the color separation optical system is a color separation optical system. An antireflection film is applied to the exit surface of at least one prism.
The color separation optical system according to claim 1, wherein the color separation optical system is a color separation optical system. A depolarizing plate disposed on the front side of the first prism to depolarize incident light in a specific direction;
The color separation optical system according to claim 1, wherein the color separation optical system is a color separation optical system. A color separation optical system that decomposes incident light into at least three color light components of blue light, red light, and green light,
  In order from the light incident side,
  A first prism that has a first dichroic film and extracts a first color light component reflected by the first dichroic film;
  A second prism that has a second dichroic film and extracts a second color light component transmitted through the first dichroic film and reflected by the second dichroic film;
  A third prism for extracting a third color light component transmitted through the first and second dichroic films;
Comprising at least
  The first dichroic film has a film configuration that reflects green light as the first color light component, and the second dichroic film has a film configuration that reflects blue light as the second color light component. And
  The slope of the reflection characteristic curve indicating the reflectance with respect to the wavelength of the first dichroic film is converted from the color matching function of the RGB color system or the chromaticity coordinates of the three primary colors of the color reproduction medium, and the like of the XYZ color system, etc. The second dichroic film has substantially the same shape within ± 10% with respect to the slope of the characteristic curve on the short wavelength side and the long wavelength side of the ideal green spectral characteristic shown by the primary conversion of the color function. The slope of the transmission characteristic curve indicating the transmittance with respect to the wavelength of the color is converted from the color matching function of the RGB color system or the chromaticity coordinates of the three primary colors of the color reproduction medium, and is subjected to the primary conversion of the color matching function of the XYZ color system. It has approximately the same shape that falls within ± 10% with respect to the slope of the characteristic curve on the short wavelength side of the ideal red spectral characteristic shown,
And,
A color separation optical system characterized in that the maximum reflectance value is 36% or more within a wavelength range of 500 nm or more and 570 nm or less in the reflection characteristic curve of the first dichroic film. . A color separation optical system that decomposes incident light into at least three color light components of blue light, red light, and green light,
  In order from the light incident side,
  A first prism that has a first dichroic film and extracts a first color light component reflected by the first dichroic film;
  A second prism that has a second dichroic film and extracts a second color light component transmitted through the first dichroic film and reflected by the second dichroic film;
  A third prism for extracting a third color light component transmitted through the first and second dichroic films;
Comprising at least
  The first dichroic film has a film configuration that reflects green light as the first color light component, and the second dichroic film has a film configuration that reflects red light as the second color light component. And
  The slope of the reflection characteristic curve indicating the reflectance with respect to the wavelength of the first dichroic film is converted from the color matching function of the RGB color system or the chromaticity coordinates of the three primary colors of the color reproduction medium, and the like of the XYZ color system, etc. The second dichroic film has substantially the same shape within ± 10% with respect to the slope of the characteristic curve on the short wavelength side and the long wavelength side of the ideal green spectral characteristic shown by the primary conversion of the color function. The slope of the reflection characteristic curve indicating the reflectance with respect to the wavelength of the color is converted from the color matching function of the RGB color system or the chromaticity coordinates of the three primary colors of the color reproduction medium, and is subjected to the primary conversion of the color matching function of the XYZ color system. It has approximately the same shape that falls within ± 10% with respect to the slope of the characteristic curve on the short wavelength side of the ideal red spectral characteristic shown,
And,
  In the reflection characteristic curve of the first dichroic film, the film structure is such that the maximum reflectance is 36% or more within a wavelength range of 500 nm to 570 nm.
 A color separation optical system.   The color separation optical system according to claim 3 or 4,
  An image sensor 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;
  An arithmetic circuit for performing an inverse transformation that reproduces a negative value in the ideal characteristic based on a signal value obtained by the image sensor;
An imaging apparatus comprising:

Images