JP4820773B2 - 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. 10 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. This color separation optical system 101 is called a Philips type color separation optical system, and sequentially from the light incident side along the optical axis Z1, an IR (infrared) cut filter 103, a first prism 110, The second prism 120 and the third prism 130 are provided, and 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. ing.

  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 122 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 on which the blue light reflecting dichroic film DB1 is formed in the first prism 110 and the light incident surface 121 in the second prism 120 have an air gap 110AG. Are arranged so as to face each other. On the incident surface 121 of the second prism 120, an antireflection film AR1 for reducing the reflection of incident light 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. 12 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. 12 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. 11 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. 12 is obtained using the color separation optical system 101 shown in FIG. 10, 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. 13 shows spectral transmission characteristics of a conventional general color separation optical system obtained by performing such a design.

  FIG. 14 shows a design example of the dichroic films DB1 and DR1 used in the conventional color separation optical system 101. As shown in FIG. 14, conventionally, as the dichroic films DB1 and DR1, the characteristic curve of 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. 15 shows spectral characteristics of a conventional color separation optical system approximated to ideal characteristics by performing such special adjustment.
JP-A-2005-208256

In the color separation optical system 101 shown in FIG. 10, a first prism 110 and second prism 120 because it is spaced air gap 110AG, as shown the concept in Figure 16, the two There is a problem in that reflection occurs at the air interface between the prisms, resulting in unnecessary ghost and flare and image quality degradation. This is caused by being transmitted through the blue light reflecting dichroic film DB1 and reflected by the incident surface 121 of the second prism 120. Here, since the blue light is reflected by the blue light reflecting dichroic film DB1, it hardly reaches the incident surface 121 of the second prism 120. Further, since the red light is also reduced by the IR cut filter 103 arranged on the front side, the red light is relatively small. Therefore, in the case of the prism arrangement as shown in FIG. 10, the incident surface 121 of the second prism 120 has the most green light. However, conventionally, as the antireflection film AR1, as shown in FIG. 6 (A), a film having a reduced reflectance in the entire visible range has been used. The reflection of light (about 600 nm) is not sufficiently suppressed. For this reason, part of the light in the wavelength region is easily reflected by the incident surface 121 of the second prism 120. Then, as shown in FIG. 16 , the light L1 that has passed through the blue light reflecting dichroic film DB1 and reentered the first prism 110 out of the reflected light is incident on the image sensor 4B for blue and is imaged. As a result, the image of the regular blue light LB is observed as a double image. Of the reflected light, the light L2 reflected by the surface 111 of the first prism 110 and reentering the second prism 120 is red light (since there is much light in the wavelength region of green light as described above). By passing through the reflective dichroic film DR1 and entering the third prism 130, and finally entering the green image sensor 4G and forming an image, a double image is formed with respect to the image of the normal green light LG. Will be observed. As described above, in the related art, although the antireflection film AR1 is provided on the incident surface 121 of the second prism 120, the characteristic for reducing the reflectance is insufficient, and therefore, between the two prisms. A ghost or the like occurs due to reflection at the air interface.

  The present invention has been made in view of such problems, and its object is to effectively reduce ghosts caused by reflection at the air interface between two prisms as compared with the prior art. The object is to provide a color separation optical system and an imaging device.

  The color separation optical system according to the present invention includes, in order from the light incident side, a first dichroic film, and a first prism that extracts a first color light component reflected by the first dichroic film from incident light. A second prism having a second dichroic film, extracting the second color light component transmitted through the first dichroic film and reflected by the second dichroic film, and transmitted through the first and second dichroic films And a third prism that extracts the third color light component, and the surface of the first prism on which the first dichroic film is formed and the light incident surface of the second prism face each other with an air space therebetween And an antireflection film that reduces reflection of light in a specific wavelength range that has passed through the first dichroic film is formed on the incident surface of the second prism. .

  In the color separation optical system according to the present invention, an antireflection film that reduces reflection of light in a specific wavelength range that has passed through the first dichroic film is formed on the incident surface of the second prism. In addition, the reflection at the air interface between the first prism and the second prism is effectively suppressed as compared with a general antireflection film that reduces the reflectance over the entire visible range. Thereby, the ghost generated due to the reflection at the air interface between the two prisms is reduced as compared with the prior art.

  In the color separation optical system according to the present invention, the first prism uses blue light as the first color light component, the second prism uses red light as the second color light component, and the third prism uses green light as the third color light component. The antireflection film formed on the incident surface of the second prism has a characteristic of reducing reflection of light in a wavelength region of at least 500 nm to 550 nm as light of a specific wavelength region. It is preferable. More specifically, it is preferable that the average reflectance of light in the wavelength range of 500 nm or more and 550 nm or less is 0.7% or less.

  The color separation optical system according to the present invention may further include an infrared cut filter that is disposed in front of the first prism and cuts infrared light.

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 reduced ghost is obtained based on each color light obtained by the color separation optical system of the present invention.

  According to the color separation optical system of the present invention, the antireflection film for reducing the reflection of the light in the specific wavelength range transmitted through the first dichroic film is formed on the incident surface of the second prism. Ghosts caused by reflection at the air interface between the two prisms can be effectively reduced as compared with the conventional case.

  According to the imaging apparatus of the present invention, since an imaging signal corresponding to the color light obtained by the high-performance color separation optical system of the present invention is output, a high-quality captured image with reduced ghost can be obtained. Can do.

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 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. 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, an IR (infrared) cut filter 3, a first prism 10, A second prism 20 and a third prism 30 are provided. The color separation optical system 1 in this embodiment is a configuration example in which the first prism 10 extracts blue light LB, the second prism 20 extracts red light LR, and the third prism 30 extracts green light LG.

  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.

  On the second surface 12 of the first prism 10, a blue light reflecting dichroic film DB2 is formed as a first dichroic film. The blue light reflecting dichroic film DB2 is configured to reflect the blue light LB as the first color light component and transmit the red light LR and the green light LG. The blue light reflecting dichroic film DB2 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. 12, 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 DB2 in the configuration example of FIG. The blue light reflecting dichroic film DB2 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 or more and 670 nm or less. 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 first surface 21 of the second prism 20 is a light incident surface. The second prism 20 is disposed with a predetermined air interval 10AG with respect to the first prism 10. More specifically, the surface 12 of the first prism 10 on which the blue light reflecting dichroic film DB2 is formed and the light incident surface 21 of the second prism 20 are arranged so as to face each other with an air gap 10AG. ing. On the incident surface 21 of the second prism 20, an antireflection film AR <b> 2 for interface reflection prevention that reduces reflection of light in a specific wavelength range that has passed through the blue light reflecting dichroic film DB <b> 2 is formed. As shown in FIG. 6A, the antireflection film AR2 for interface reflection prevention has a specific wavelength range, in particular, compared to the conventional antireflection film AR1 in which the reflectance is reduced over the entire visible range. The light has a characteristic of further reducing reflection of light in a wavelength region of at least 500 nm to 550 nm. More specifically, it is preferable that the average reflectance of light in the wavelength range of 500 nm or more and 550 nm or less is 0.7% or less. FIG. 6B shows numerical data of a specific film design example of the antireflection film AR2. In FIG. 6B, “Sub-H4” represents a substance H4 (manufactured by Merck & Co., Germany) whose main component is LaTiO ₃ . However, the film substance, the number of layers, and the film thickness of each layer are not limited to the example of FIG.

  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.

  On the second surface 22 of the second prism 20, a red light reflecting dichroic film DR2 is formed as a second dichroic film. The red light reflecting dichroic film DR2 is configured to reflect the red light LR as the second color light component and transmit the green light LG. The red light reflecting dichroic film DR2 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 DR2 in the configuration example of FIG. The red light reflecting dichroic film DR2 has a transmission characteristic curve whose slope is along 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.

  FIG. 3 shows characteristics in a specific design example of the blue light reflecting dichroic film DB2 and the red light reflecting dichroic film DR2 used in the color separation optical system 1. Among the characteristics shown in FIG. 3, the characteristics of the blue light reflecting dichroic film DB2 and the red light reflecting dichroic film DR2 are obtained by, for example, 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.

  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 red light reflecting dichroic film DR2. 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 red light reflecting dichroic film DR2. 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. More specifically, first, the blue light LB in the incident light L is reflected by the blue light reflecting dichroic film DB2 and is extracted from the first prism 10 as the first color light component. Further, the red light LR transmitted through the blue light reflecting dichroic film DB2 is reflected by the red light reflecting dichroic film DR2, and is extracted from the second prism 20 as the second color light component. Further, the green light LG transmitted through the blue light reflecting dichroic film DB2 and the red light reflecting dichroic film DR2 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.

Here, in the conventional color separation optical system (FIG. 10) using a trimming filter with a dichroic film on the exit surface of the prism, the wavelength characteristic of the dichroic film has a wavelength range with high reflectivity. There is a problem that multiple reflection occurs between the dichroic surface and the imaging surface, resulting in ghost and flare and image quality deterioration. FIG. 17 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. 17 , for example, a part of the green light LG that has passed through the green trimming filter 153 is reflected by the imaging surface 401G of the imaging device 4G , and the return light is the wavelength of the dichroic film 153A of the trimming filter 153. Reflected according to the selection characteristics. As this becomes ghost flare occurs multiple reflection light 160. For this reason, conventionally, it has been difficult to realize an imaging system having ideal spectral characteristics with reduced ghost and flare.

  On the other hand, in the present embodiment, the curve indicating the characteristic of the blue light reflecting dichroic film DB2 and the curve indicating the characteristic of the red light reflecting dichroic film DR2 have shapes that conform to the characteristic curve of the ideal green spectral characteristic. By having it, 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.

  Further, in the present embodiment, the interface surface anti-reflection for reducing the reflection of light in a specific wavelength region near 500 nm to 600 nm on the incident surface 21 of the second prism 20 as compared with the conventional anti-reflection film AR1. Therefore, the reflection at the air interface between the first prism 10 and the second prism 20 is effectively suppressed.

  FIG. 8 shows an evaluation of the amount of ghost (double image) generated in the color separation optical system 1 according to this embodiment as compared to the case where the conventional antireflection film AR1 is used. 8 have the characteristics shown in FIG. 6A as the antireflection films AR1 and AR2, and have the characteristics shown in FIG. 7 as the IR cut filter 3 and the blue light reflecting dichroic film DB2. The evaluation when using is shown.

In FIG. 8, a characteristic curve denoted by reference numeral 81 is an evaluation of a double image observed by the blue image sensor 4B in the color separation optical system 1 according to the present embodiment. This is the light that has passed through the blue light reflecting dichroic film DB2 and is reflected by the incident surface 21 of the second prism 20 and reaches the blue image sensor 4B (light corresponding to the light L1 in FIG. 16 ). ) Percentage. For comparison, a characteristic curve denoted by reference numeral 83 indicates characteristics when the conventional antireflection film AR1 is used for the incident surface 21 of the second prism 20. As can be seen, when the antireflection film AR2 for preventing interface reflection in the present embodiment is used, the occurrence of double images observed with the blue image sensor 4B is greatly reduced.

In FIG. 8, a characteristic curve denoted by reference numeral 82 is an evaluation of a double image observed by the green image sensor 4G in the color separation optical system 1 according to the present embodiment. This is that the light transmitted through the blue light reflecting dichroic film DB2 is reflected by the incident surface 21 of the second prism 20 and reflected by the second surface 12 of the first prism 10, and the second prism 20 is reflected. The ratio of the light (light corresponding to the light L2 in FIG. 16 ) that passes through the third prism 30 and reaches the green image sensor 4G is shown. For comparison, characteristics when the conventional antireflection film AR1 is used for the incident surface 21 of the second prism 20 are shown in a characteristic curve denoted by reference numeral 84. As can be seen, when the antireflection film AR2 for preventing interface reflection in the present embodiment is used, the occurrence of double images observed with the green image sensor 4G is greatly reduced.

As described above, according to the color separation optical system 1 according to the present embodiment, the specific wavelength transmitted through the first dichroic film (blue light reflecting dichroic film DB2) on the incident surface 21 of the second prism 20. Since the antireflection film AR2 for reducing the reflection of the light in the region is formed, the ghost generated due to the reflection at the air interface between the two prisms can be effectively reduced as compared with the conventional case. 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, the ghost is reduced. A high quality photographed image can be obtained.
<Modification>

In addition, this invention is not limited to the said embodiment, A various deformation | transformation implementation is possible.
For example, the antireflection film AR2 for preventing interface reflection in the present embodiment can be used in the conventional color separation optical system shown in FIG.

  FIG. 9 shows an evaluation of the amount of ghost (double image) generated in the conventional color separation optical system shown in FIG. 10 in comparison with the case where the conventional antireflection film AR1 is used. 9 have the characteristics shown in FIG. 6A as the antireflection films AR1 and AR2, and have the characteristics shown in FIG. 7 as the IR cut filter 3 and the blue light reflecting dichroic film DB1. The evaluation when using is shown.

In FIG. 9, a characteristic curve denoted by reference numeral 91 indicates a blue image pickup element when the antireflection film AR2 for preventing interface reflection in the present embodiment is used in the conventional color separation optical system shown in FIG. The double image observed in 4B is evaluated. This is the light that has passed through the blue light reflecting dichroic film DB1 and is reflected by the incident surface 121 of the second prism 120 and reaches the blue image sensor 4B (light corresponding to the light L1 in FIG. 16 ). ) Percentage. For comparison, characteristics when the conventional antireflection film AR1 is used for the incident surface 121 of the second prism 120 are shown in a characteristic curve denoted by reference numeral 93. As can be seen from this, even when applied to the conventional color separation optical system shown in FIG. 10, when the antireflection film AR2 for preventing interface reflection in the present embodiment is used, imaging for blue is performed. The occurrence of double images observed with element 4B is greatly reduced.

In FIG. 9, the characteristic curve denoted by reference numeral 92 is for green when the antireflection film AR2 for preventing interface reflection in the present embodiment is used in the conventional color separation optical system shown in FIG. The double image observed with the image sensor 4G is evaluated. Of the light transmitted through the blue light reflecting dichroic film DB1, this is reflected by the incident surface 121 of the second prism 120 and reflected by the surface 111 of the first prism 110, and the second prism 120 and the third prism The ratio of light that passes through the prism 130 and reaches the green image sensor 4G (light corresponding to the light L2 in FIG. 16 ) is shown. For comparison, characteristics when the conventional antireflection film AR1 is used for the incident surface 121 of the second prism 120 are shown in a characteristic curve denoted by reference numeral 94. As can be seen from this, even when applied to the conventional color separation optical system shown in FIG. 10, when the antireflection film AR2 for preventing interface reflection in the present embodiment is used, imaging for green is performed. The occurrence of double images observed with element 4G is greatly reduced.

  The present invention can also be applied to a color separation optical system in which the order of extracting colored light and the arrangement of prisms are different from those shown in FIGS.

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 blue light reflection dichroic film | membrane DB2 used with the color separation optical system shown in FIG. 1, and the characteristic (B) of red light reflection dichroic film | membrane DR2. FIG. 2 is a characteristic diagram showing a design example of a blue light reflecting dichroic film DB2 and a red light reflecting dichroic film DR2 used in the color separation optical system shown in FIG. It is a figure which shows the numerical example of the film | membrane design of the blue light reflection dichroic film | membrane DB2 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 DR2 used with the color separation optical system shown in FIG. FIG. 6 is a characteristic diagram showing a comparison between the characteristics of the antireflection film AR2 and the characteristics of the conventional antireflection film AR1 and an example of film data of the antireflection film AR2. It is a characteristic view about optical elements other than the antireflection film relevant to ghost evaluation. 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 compared to a conventional antireflection film. FIG. 6 is a characteristic diagram comparing the characteristics when an antireflection film AR2 according to an embodiment of the present invention and a conventional antireflection film AR1 are applied to a conventional color separation optical system. 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 ghost resulting from the air interface between two prisms 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

AR2: antireflection film for interface reflection prevention, L: incident light, LB ... blue light component, LR ... red light component, LG ... green light component, DB2 ... blue light reflecting dichroic film, DR2 ... red light reflecting dichroic film, 1 ... color separation optical system, 2 ... photographing lens, 3 ... IR cut filter, 4R, 4G, 4B ... imaging element, 10 ... first prism, 20 ... second prism, 30 ... third prism, 51 ... first 1 trimming filter, 52 ... second trimming filter, 53 ... third trimming filter, 51AR ... first antireflection film, 52AR ... second antireflection film, 53AR ... third antireflection film.

Claims (5)

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 from incident light;
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 surface of the first prism on which the first dichroic film is formed and the light incident surface of the second prism are arranged so as to face each other with an air gap between them,
An anti-reflection film that reduces reflection of light in a specific wavelength range that has passed through the first dichroic film is formed on the incident surface of the second prism. 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
The antireflection film formed on the incident surface of the second prism has a characteristic of reducing reflection of light in a wavelength region of at least 500 nm to 550 nm as light in the specific wavelength region. The color separation optical system according to claim 1. The color separation optical system according to claim 2, wherein the antireflection film has an average reflectance of light in a wavelength region of 500 nm or more and 550 nm or less of 0.7% or less. The color separation optical system according to claim 2, further comprising an infrared cut filter that is disposed in front of the first prism and cuts infrared light. The color separation optical system according to any one of claims 1 to 4,
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.

Images