JP2011248047A - Color separation optical system and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color separation optical system capable of reducing a ghost image without using an anti-reflection film.SOLUTION: The color separation optical system 1 separates an incident light into three color light components: a blue light component LB, a red light component LR, and a green light component GR. The color separation optical system 1 is provided with a first prism 10, a second prism 20, and a third prism 30 sequentially from the light incident side. The first prism 10 reflects the blue light component LB with a blue light reflection dichroic film DB provided on a second surface 12 thereof and extracts the blue light component LB. The second prism 20 transmits the green light component LG with a red light reflection dichroic film DR provided on a second surface 22 thereof while reflects the red light component LR and extracts the red light component LR. The third prism 30 extracts the green light component LG. The reflectance of the red light reflection dichroic film DR varies from 10% to 90% within a wavelength range of 10 nm or below in a wavelength region of 560 nm to 600 nm (both inclusive).

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. 5 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 charge coupled device (CCD) are disposed 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.

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

  Usually, a protective cover glass is provided on the surface of the image sensor. However, unnecessary light reflected by the surface of the cover glass may return to the first to third prisms 110, 120, and 130, and the reflected light of the unnecessary light may enter the image sensor again. For example, in the color separation optical system of FIG. 5, after unnecessary light reflected on the cover glass (not shown) of the image sensor 4G returns to the third prism 130 and secondarily reflects on the reflection surface (transmission surface) 121. In some cases, the light enters the image sensor 4G again. When such secondary reflected light enters the image sensor, for example, a ghost image as shown in FIG. 6 is generated and the image quality is deteriorated. In FIG. 6, a ghost image having a green color appears in a semicircular region with a pattern. Such a ghost image depends on the spectral characteristics of the red light reflecting dichroic film DR1 (see FIG. 7). FIG. 7 shows the wavelength dependency of the transmittance (solid line) and the reflectance (broken line) of the red light reflecting dichroic film DR1. Here, the light intensity just before entering the second prism 120 or the third prism 130 is 100%. In FIG. 7, it is considered that the wavelength light in the overlapping region GH1 (patterned region) of the transmittance distribution and the reflectance distribution appears as a ghost image.

  Therefore, in order to remove such a ghost image, the following proposals have been conventionally made. For example, Patent Document 1 discloses a technique in which an antireflection film is coated on the surface of a cover glass and the cover glass itself is made of colored glass. Further, in the color separation optical system of Patent Document 2, the transmittance characteristic curve of the color separation prism and the reflectance characteristic curve of the dichroic film are determined so that the transmittance of the color separation prism and the reflectance of the dichroic film are both 10% or less. In such a wavelength range.

Utility Model No. 2585974 JP 2000-98442 A

  However, when the antireflection film is employed as in Patent Document 1, the configuration becomes complicated and the manufacturing process becomes complicated, which is disadvantageous in terms of manufacturing cost. Further, Patent Document 2 described above suppresses ghost light that is secondarily reflected by the surface on which the dichroic film of the trimming filter is formed, and is secondary by the reflection surface (transmission surface) 121 in the color separation optical system of FIG. The reflected ghost light cannot be reduced. Further, in the color separation optical system as shown in FIG. 5, the secondary reflected light from the reflection surface (transmission surface) 121 enters the image sensor 4G by appropriately changing the angle of the reflection surface (transmission surface) 121. It is possible to avoid it. However, due to the structural limitations of the image pickup apparatus equipped with the color separation optical system, it is necessary to reduce the space for arranging the color separation optical system as much as possible. Is in the situation.

  The present invention has been made in view of such a problem, and an object thereof is to provide a color separation optical system and an imaging apparatus capable of reducing a ghost image without using an antireflection film.

  The color separation optical system of the present invention separates incident light into at least three color light components of blue light, red light, and green light, and has a first dichroic film in order from the light incident side, A first prism that extracts a first color light component reflected by the first dichroic film, and a second prism that is transmitted through the first dichroic film and then reflected by the second dichroic film. At least a second prism that extracts the color light component of the first color, and a third prism that extracts the third color light component that has passed through the first and second dichroic films. The first dichroic film reflects blue light or green light as the first color light component, and the second dichroic film reflects red light as the second color light component. Here, the reflectance of the second dichroic film changes from 10% to 90% in a wavelength range of 10 nm or less in a wavelength range of 560 nm to 600 nm. The image pickup apparatus of the present invention is provided corresponding to the color separation optical system of the present invention and each color light separated by the color separation optical system, and outputs an electric signal corresponding to each color light incident thereon. And an element.

  In the color separation optical system and the imaging device of the present invention, the reflectance of the second dichroic film provided on the second prism is 10% to 90% in a wavelength range of 10 nm or less in a wavelength range of 560 nm to 600 nm. % To change. For this reason, out of the third color light components transmitted through the first dichroic film and the second dichroic film in this order, they reenter the third prism as return light, and are secondarily reflected by the second dichroic film. The intensity of the component that becomes unnecessary light is sufficiently reduced. That is, the total intensity of unnecessary light visually recognized as a ghost image is sufficiently reduced.

  In the color separation optical system and the imaging device of the present invention, the reflectance of the second dichroic film may be changed from 10% to 90% in a wavelength range of 10 nm or less included in a wavelength range of 570 nm to 585 nm. . The maximum slope in the reflectance characteristic curve of the second dichroic film is preferably 8% / nm or more.

  According to the color separation optical system of the present invention and the imaging apparatus including the same, the reflectance of the second dichroic film provided on the second prism that extracts the second color light component is steep in a predetermined wavelength range. Since the change is shown, the intensity of the ghost image due to the secondary reflection at the second dichroic film can be sufficiently reduced without adding other components such as an antireflection film. For this reason, although it is a simple structure, the favorable image quality in which the ghost image was fully reduced can be obtained.

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 a characteristic view showing the transmittance | permeability (reflectance) distribution of the red light reflection dichroic film | membrane used with the color separation optical system shown in FIG. It is the characteristic view which expanded and represented the transmittance | permeability distribution of the red light reflection dichroic film | membrane shown in FIG. FIG. 3 is an enlarged characteristic diagram illustrating an overlapping region illustrated in FIG. 2. It is sectional drawing which shows one structural example of the imaging device provided with the conventional color separation optical system. FIG. 6 is a conceptual diagram schematically illustrating a ghost image generated in an imaging apparatus including the color separation optical system illustrated in FIG. 5. FIG. 6 is a characteristic diagram showing a transmittance (reflectance) distribution of a red light reflecting dichroic film used in the color separation optical system shown in FIG. 5.

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

  FIG. 1 shows a main configuration of an image pickup apparatus including a color separation optical system 1 as an embodiment of the present invention. This imaging device is used as an imaging part of a television camera, for example. The color separation optical system 1 decomposes incident light L incident through the photographing lens 2 into three color light components, a blue light component LB, a red light component LR, and a green light component 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 according to the present 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. As shown in FIG. 1, a trimming filter 51 for adjusting spectral characteristics may be provided on the light emission surface (third surface 13).

  A blue light reflecting dichroic film DB as a first dichroic film is formed on the second surface 12 of the first prism 10. The blue light reflecting dichroic film DB has a property of reflecting the blue light component LB as the first color light component and transmitting the red light component LR and the green light component LG.

  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. As shown in FIG. 1, a trimming filter 52 for adjusting spectral characteristics may be provided on the light exit surface (third surface 23).

  A red light reflecting dichroic film DR as a second dichroic film is formed on the second surface 22 of the second prism 20. The red light reflecting dichroic film DR has a property of reflecting the red light component LR as the second color light component and transmitting the green light component LG.

  FIG. 2 shows an example of the transmittance characteristic curve (displayed by a solid line) and the reflectance characteristic curve (displayed by a broken line) of the red light reflecting dichroic film DR in the configuration example of FIG. FIG. 3 is an enlarged view of the transmittance characteristic curve in the partial wavelength range (550 nm to 610 nm) of FIG. 2 and 3, the horizontal axis represents wavelength (nm), and the vertical axis represents transmittance (%) or reflectance (%). Here, the light intensity immediately before entering the second prism 20 or the third prism 30 is 100%. As shown in FIG. 3, the reflectance (transmittance) of the red light reflecting dichroic film DR is configured to change rapidly from 10% to 90% in a slight wavelength range BW of 10 nm or less. More specifically, a steep change is exhibited from a position P1 at a wavelength of 573 nm where the transmittance is 90% to a position P2 at a wavelength of 582 nm where the transmittance is 10%. Further, in the wavelength region of 570 nm or more and 585 nm or less, the transmittance sharply decreases from at least 98% to 2%. The maximum slope in the reflectance (transmittance) characteristic curve of the red light reflecting dichroic film DR is preferably 8% / nm or more (−8% / nm or less).

  Table 1 shows a configuration example of the red light reflecting dichroic film DR from which the transmittance (reflectance) characteristic curves of FIGS. 2 and 3 are obtained. However, the number of layers of the multilayer film constituting the red light reflecting dichroic film DR, the constituent material and the thickness of each layer are not limited to those shown in Table 1.

  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 DR. 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 DR. The second surface 32 of the third prism 30 is a light exit surface. As shown in FIG. 1, a trimming filter 53 for adjusting spectral characteristics may be provided on the light emission surface (third surface 32).

  The IR cut filter 3 is disposed on the incident 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 incident 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. Further, the IR cut filter 3 may be arranged on both the incident 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 for cutting 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.

  Although not shown, the color separation optical system 1 may further include an absorption type or coat type ultraviolet cut filter for cutting ultraviolet light on the incident side of the first prism 10.

  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, a blue light component LB, a red light component LR, and a green light component LG. More specifically, first, the blue light component LB of the incident light L is reflected by the blue light reflecting dichroic film DB and extracted from the first prism 10 as the first color light component. Further, the red light component LR transmitted through the blue light reflecting dichroic film DB is reflected by the red light reflecting dichroic film DR, and is extracted from the second prism 20 as the second color light component. Further, the green light component LG transmitted through the blue light reflecting dichroic film DB and the red light reflecting dichroic film DR is extracted from the third prism 30 as the third color light component. The respective color light components separated by the color separation optical system 1 are incident on the image pickup devices 4B, 4R, 4G provided corresponding to the respective color light components. The imaging elements 4B, 4R, and 4G output electrical signals corresponding to the incident color light components as imaging signals.

  In the present embodiment, a part of the green light LG incident from the first surface 21 and transmitted through the red light reflecting dichroic film DR is reflected by the cover glass surface of the image sensor 4G, and then the red light reflecting dichroic film DR. Secondary reflection occurs. The secondary reflected light generated in this way is, of course, included in the wavelength range showing the property of being transmitted through the red light reflecting dichroic film DR at a certain ratio and reflected at the red light reflecting dichroic film DR at a certain ratio. That is, light in a wavelength range corresponding to the transmittance characteristic curve (solid line), the reflectance characteristic curve (broken line), and the overlapping region GH (patterned region) surrounded by the horizontal axis shown in FIG. appear. However, in the present embodiment, the reflectance (transmittance) of the red light reflecting dichroic film DR changes rapidly from 10% to 90% in a slight wavelength range of 10 nm or less (for example, a range of 573 nm or more and 582 nm or less). Thus, the peak half-value width of the region is greatly narrowed. For this reason, as shown in FIG. 4, the area of the overlapping region GH is significantly reduced as compared with the conventional overlapping region GH1, and the ghost image can be sufficiently reduced. FIG. 4 shows the intensity distribution of the ghost image, and shows the region GH shown in FIG. 2 and the region GH1 shown in FIG. When the transmittance changes from 10% to 90%, the wavelength range exceeds 10 nm (that is, when the transmittance characteristic curve shows a gentler slope than that shown in FIG. 3). The ghost image cannot be reduced sufficiently. On the other hand, if the wavelength range when the transmittance changes from 10% to 90% is about 10 nm, it can be produced by the same manufacturing technology as the conventional dichroic film, and the variation in quality is increased. Therefore, mass productivity is not impaired.

  As described above, in the present embodiment, the reflectance (transmittance) of the red light reflecting dichroic film DR shows a steep change in a predetermined wavelength range included in a predetermined wave region. The intensity of the ghost image can be sufficiently reduced without adding other components. For this reason, although it is a simple structure, the favorable image quality in which the ghost image was fully reduced can be obtained.

  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 ... color Decomposing optical system, 2 ... photographing lens, 3 ... IR cut filter, 4R, 4G, 4B, 4C ... imaging device, 10 ... first prism, 20 ... second prism, 30 ... third prism, 51-53 ... First to third trimming filters.

Claims (4)

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 having a second dichroic film, and extracting a second color light component reflected by the second dichroic film after passing through the first dichroic film;
And a third prism for extracting a third color light component that has passed through the first and second dichroic films,
The first dichroic film reflects blue light as the first color light component, and the second dichroic film reflects red light as the second color light component,
The color separation optical system in which the reflectance of the second dichroic film changes from 10% to 90% in a wavelength range of 10 nm or less in a wavelength range of 560 nm to 600 nm.   The color separation optical system according to claim 1, wherein the wavelength range is included in a wavelength range of 570 nm to 585 nm.   3. The color separation optical system according to claim 1, wherein a maximum inclination in a reflectance characteristic curve of the second dichroic film is 8% / nm or more. The color separation optical system according to any one of claims 1 to 3,
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