JP4610324B2 - Color separation optical system - Google Patents

Description

  The present invention relates to a color separation optical system used in an imaging apparatus such as a TV camera or a video camera, and more specifically, is configured by combining a plurality of prisms and wavelength selection filters, and incident light is divided by spectral characteristics of these optical elements, The present invention relates to a color separation optical system that decomposes light into a plurality of wavelength ranges (for example, blue light, green light, and red light) and emits the decomposed light toward a solid-state imaging device or the like.

  Conventionally, this type of color separation optical system has various types such as a type called a Philips type and a type called a cross dichroic type, depending on the combination of a plurality of prisms and an optical filter film for color separation. It has been known.

  In recent years, in an imaging apparatus such as a television camera incorporating this type of color separation optical system, a solid-state imaging element such as a CCD is used instead of an imaging tube as an imaging element that converts the captured optical image into an electrical signal. ing. A technique that was difficult when using an imaging tube that is prone to problems such as so-called burn-in, i.e., taking a high-luminance subject image into a color separation optical system and performing color separation, In such a state, it is possible to easily perform the method of injecting the image onto the imaging surface of each solid-state imaging device.

  However, the imaging surface of the solid-state imaging device has a high reflectance such as a metal coating film, and when high-intensity light is incident on the imaging surface, this light is reflected by the imaging surface and the color separation optical system There is a tendency that the reflected light returns to the light exit surface, and the reflected light is reflected again by the light exit surface and incident again on the image capturing surface of the solid-state image sensor. Such light reciprocation between the light exit surface of the color separation optical system and the image pickup surface of the solid-state image pickup device causes ghosts and flares and causes an adverse effect on the image.

  In view of this, a means for controlling ghost and flare has been proposed by arranging a trimming filter made of colored glass for removing unnecessary component light on the light exit surface of the color separation optical system (see, for example, Patent Document 1). ).

In addition, a technique has also been proposed in which a trimming filter made of color glass for removing unnecessary component light is arranged on the surface of a protective glass of a solid-state imaging device made of a CCD or the like instead of the light emission surface of the color separation optical system. (For example, see Patent Document 2)
Japanese Patent Laid-Open No. 10-234049 JP-A-9-37116

However, in the technique described in Patent Document 1, since the spectral characteristics of the colored glass depend on the thickness of the colored glass, it is possible to satisfy both the spectral characteristics required for the colored glass and the mechanical restrictions on the thickness at the same time. It was difficult. Moreover, even if the spectral characteristics required for the colored glass and the mechanical constraints on the thickness can be satisfied at the same time, the components of the material for producing the colored glass are limited, and the thermal expansion of the colored glass is limited. The degree of freedom regarding other physical properties such as coefficient and refractive index was small.
In order to cope with such an inconvenience, the inventors of the present application have developed a color separation optical system using a trimming filter having a light absorption layer containing a pigment instead of color glass.

  However, the light absorption layer containing a pigment has a characteristic that spectral transmittance is lower than that of colored glass. Since the human eye is particularly sensitive to green light, color separation with good color balance is achieved when a light-absorbing layer containing a pigment is used for the prism that emits green light from the light exit surface. In some cases, the optical system could not be used.

  With reference to FIG. 3, the spectral transmittance of green light in a conventional color separation optical system will be described. FIG. 3 shows a conventional color separation optical system that includes a dichroic film that reflects red light and transmits green light (hereinafter referred to as a red reflection / green transmission dichroic film), colored glass, and a pigment. It is explanatory drawing which shows the spectral transmittance curve of an absorption layer. In FIG. 3, the spectral transmittance curve of the red reflection / green transmission dichroic film is indicated by a solid line, the spectral transmittance curve of the colored glass is indicated by a one-dot chain line, and the spectral transmittance curve of the light absorption layer containing the dye is indicated by a broken line. Is shown.

  As shown in FIG. 3, the red reflection / green transmission dichroic film used in the conventional color separation optical system has a falling half-value of the spectral transmittance curve in the vicinity of the wavelength of 575 nm with respect to the green region light. On the side, the spectral transmission range of green light cannot be defined. Therefore, by using a colored glass or a light absorbing layer containing a pigment, the green region light transmission range (reflection of red region light is reflected so as to have a rising half value of the spectral transmittance curve near the wavelength of 490 nm with respect to the green region light. Range).

By the way, as shown in FIG. 3, when colored glass is used, the spectral transmittance curve rises steeply on the short wavelength side of the green region, and the light transmittance is nearly 100% from around the wavelength of 520 nm. Thus, good optical performance was exhibited.
However, as described above, when a light absorbing layer containing a dye is used, the maximum value of the spectral transmittance on the long wavelength side of the green region is about 88%, and the sensitivity of the human eye is particularly high. A color separation optical system having a good color balance with respect to green light could not be obtained.

  Further, depending on the characteristics of the wavelength selection filter (for example, dichroic film) constituting the color separation optical system, some unnecessary light may remain in the incident light to the prism. For example, in the light incident on the prism that emits red light from the light exit surface, some unnecessary light may remain on the blue light side, and in order to remove this unnecessary light, It is necessary to provide a trimming filter on the light exit surface side of the prism.

  As described above, in the conventional color separation optical system described in Patent Document 2, the color glass is pasted on the surface of the protective glass of the solid-state imaging device. However, since the color glass has a certain thickness, Sufficient space is required between the solid-state imaging device and it is difficult to downsize the color separation optical system. In addition, there is a problem that the degree of freedom in selecting a material used for the colored glass is small.

  The present invention has been proposed in view of the above-described circumstances, and emits green light from the light exit surface by adjusting the spectral characteristics of a wavelength selection filter that transmits green light and reflects red light. An object of the present invention is to provide a color separation optical system that suppresses ghosts and flares and has a good color balance without using a light absorbing layer containing colored glass or a pigment in the prism.

  In addition, the present invention suppresses ghosts and flares and reduces color balance even when there is a prism that requires a trimming filter on the light exit surface side in order to remove unwanted light. An object of the present invention is to provide a color separation optical system that is favorable and can be miniaturized.

In order to achieve the above-described object, the color separation optical system of the present invention includes a first prism, a second prism, and a third prism arranged in order from the light incident side , and a predetermined prism of the prism. In a color separation optical system including a plurality of wavelength selection filters disposed on a surface and having different spectral characteristics that selectively transmit or reflect light in a predetermined wavelength range,
Among the wavelength selective filter, wherein the second prism is provided at the interface between the third prism, the wavelength selective filter having a spectral property of transmitting green region light while reflecting red region light, its spectral In the transmittance curve , the rising half-value wavelength on the short wavelength side of green light is set in the range of 480 nm to 510 nm, and the wavelength having a transmittance of 15% on the short wavelength side across the rising half-value wavelength The difference from the wavelength having a transmittance of 80% on the long wavelength side is set within 30 nm .

Still another color separation optical system of the present invention is disposed on a predetermined prism surface of the first prism, the second prism, and the third prism, which are sequentially disposed from the light incident side , In a color separation optical system including a plurality of wavelength selection filters having different spectral characteristics that selectively transmit or reflect light in a predetermined wavelength range,
The wavelength selection filter has spectral characteristics the provided opposite the light reflecting surface to the light incident surface of the second prism in the first prism, and transmits the red band light and green region light while reflecting the blue band light A wavelength selective filter having :
A wavelength selective filter provided at a boundary surface between the second prism and the third prism, having a spectral characteristic that reflects red light and transmits green light;
The wavelength selective filter having the spectral characteristic of reflecting the red light and transmitting the green light has a rising half-value wavelength on the short wavelength side of the green light within the range of 480 nm to 510 nm in the spectral transmittance curve. The difference between the wavelength having a transmittance of 15% on the short wavelength side and the wavelength having a transmittance of 80% on the long wavelength side is set within 30 nm across the rising half-value wavelength . It is characterized by .

In addition, a solid-state imaging device is disposed to face the light exit surfaces of the plurality of prisms,
Among the plurality of prisms, there is no need to be included in the incident light to the solid-state image sensor between the light exit surface and the light-receiving surface of the solid-state image sensor disposed facing the prism that emits red light. It is possible to provide a coating layer containing a dye having spectral characteristics that removes light in various wavelength ranges.

  According to the color separation optical system of the present invention, for a wavelength selection filter that transmits green light, the spectral transmittance curve is at the short wavelength side of the green light and at the boundary between blue light and green light. By adding a transmission characteristic that rises along the line, it is possible to remove unwanted light by appropriately adjusting the spectral characteristics without using a light absorbing layer containing colored glass or pigment, thereby suppressing ghosts and flares. At the same time, the color balance can be improved.

  For the spectral transmittance curve in the wavelength selective filter having spectral characteristics that transmits green light, the rising half-value on the short wavelength side is set within a range of 480 nm to 510 nm, and the rising half-value wavelength is sandwiched between the short wavelength By setting the difference between the wavelength having a transmittance of 15% on the side and the wavelength having a transmittance of 80% on the long wavelength side to be within 30 nm, it is possible to more reliably and effectively suppress ghosts and flares, The color balance can be made good.

  In addition, a coating containing a pigment having a spectral characteristic for removing unnecessary blue light contained in incident light on a light receiving surface of a solid-state imaging device disposed opposite to a prism that emits red light from a light emitting surface By providing the layer, it is possible to further reduce ghosts and flares, improve the color balance, and achieve a color separation optical system that can be reduced in size.

Embodiments of the color separation optical system of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing a color separation optical system according to an embodiment of the present invention.

  As shown in FIG. 1, a color separation optical system according to an embodiment of the present invention includes a Philips color separation prism 10 disposed on an optical path L of incident light carrying image information of a subject (not shown). The color separation prism 10 includes three prisms, a blue separation prism 11, a red separation prism 12, and a green separation prism 13.

  The blue solid-state imaging element 14B is positioned at a position facing the blue color light emitting surface 11a of the blue separation prism 11, and the red solid-state imaging is positioned at a position facing the red color light emitting surface 12a of the red separation prism 12. A green solid-state image sensor 14G is disposed at a position where the element 14R faces the green light exit surface 13a of the green separation prism 13.

  Further, the reflection prism surface of the blue separation prism 11 reflects only light in the short wavelength light region (blue region light) including blue region light, and light in the intermediate wavelength region (green region light) including green region light and A first dichroic film 15 that transmits light in a long wavelength region (red region light) including red region light is disposed. Furthermore, the light within the wavelength range of the red light among the light incident on the red separation prism 12 is reflected on the reflecting prism surface located at the boundary between the red separation prism 12 and the green separation prism 13, and the red region. A second dichroic film 16 having a spectral characteristic for transmitting light outside the light wavelength range (mainly green light) is disposed.

The first dichroic film 15 and the second dichroic film 16 are made of a well-known dichroic film adjusted to have a predetermined spectral characteristic. For example, a plurality of film layers made of TiO ₂ and SiO ₂ are alternately laminated. It has a structure.

  In addition, a red region light emission surface between the red region light emission surface 12a of the red separation prism 12 and the imaging surface of the red solid-state imaging device 14R disposed to face the red region light emission surface 12a. A coating layer 121 containing a pigment having spectral characteristics for removing unnecessary wavelength band light contained in a minute amount in the emitted light from 12a is formed. The coating layer 121 is obtained by attaching a dye to the surface of the optical glass 120 by a spin coating method, a vacuum deposition method, or the like. In addition, the number of parts can be reduced by providing a coating layer containing this pigment on a cover glass of a CCD.

  Light from a subject (not shown) is incident along the optical path L from the incident prism surface 11b of the blue separation prism 11 and reaches the first dichroic film 15. In the first dichroic film 15, the blue region Only the light B is reflected, and the green color light G and the red color light R are transmitted. The blue color light B reflected by the first dichroic film 15 is totally reflected by the incident prism surface 11b, then exits from the blue color light exit surface 11a, and is imaged by the blue solid-state imaging device 14B.

  On the other hand, the green color light G and the red color light R transmitted through the first dichroic film 15 are reflected by the second dichroic film 16 and the green color light G is transmitted. The transmitted green light G is emitted from the green light emitting surface 13a through the green separation prism 13, and is imaged by the green solid-state imaging device 14G.

  Further, since the red gap light R reflected by the second dichroic film 16 has an air gap between the blue separation prism 11 and the red separation prism 12, the total reflection prism surface 12b of the red separation prism 12 is provided. Are totally reflected, emitted from the red light exit surface 12a, and imaged by the red solid-state imaging device 14R.

  Here, as a characteristic of the second dichroic film 16, light that is incident on the red separation prism 12 and is emitted from the light emission surface 12a of the red color region includes a small amount of unnecessary wavelength range light. . Therefore, unnecessary wavelength band light is emitted by the coating layer 121 provided between the red color light emitting surface 12a and the imaging surface of the red solid-state image pickup device 14R disposed to face the red color light emitting surface 12a. Absorption prevents a light reciprocation between the light exit surface 12c of the optical glass 120 and the light receiving surface of the red solid-state imaging device 14R, and is free from ghosts and flares and is a good image with little crosstalk. Can be obtained.

Next, with reference to FIG. 2, spectral characteristics in the color separation optical system of this embodiment will be described.
FIG. 2 is an explanatory diagram showing the spectral characteristics of the second dichroic film used in the color separation optical system of the present invention.

  In the color separation optical system of the present embodiment, as shown in FIG. 2, the second dichroic film 16 has a rising half-value wavelength of about 495 nm and a falling half-value wavelength of the spectral transmittance curve of 575 nm. It is set to be about. Further, the wavelength having 15% transmittance on the short wavelength side is about 490 nm across the rising half-value wavelength, and the wavelength having 80% transmittance on the long wavelength side is about 498 nm. Therefore, the difference between them is about 8 nm.

  Furthermore, as shown in FIG. 2, it has a spectral transmittance of about 97% to 100% in the maximum region of the spectral transmittance of green light. Therefore, according to the color separation optical system of the present embodiment, the color balance can be improved with respect to the sensitivity of the human eye.

  Further, as a color separation optical system according to another embodiment, in the first dichroic film 15, as in the case of the second dichroic film 16, the rising half value of the spectral transmittance curve is set to a wavelength of about 495 nm. By doing so, it is possible to add a transmission characteristic that rises along the boundary between the blue light and the green light on the short wavelength side of the green light. Also in this case, the difference between the wavelength having a transmittance of 15% and the wavelength having a transmittance of 80% on the short wavelength side across the rising half-value wavelength of the spectral transmittance curve on the short wavelength side of the green light. Is set within 30 nm.

  In the color separation optical system of the present invention, the rising half-value wavelength on the short wavelength side is set in the range of 480 nm to 510 nm in the spectral transmittance curve, and 15 on the short wavelength side across the rising half-value wavelength. If the difference between the wavelength having a transmittance of% and the wavelength having a transmittance of 80% on the long wavelength side is set within 30 nm, the color balance can be improved.

  In addition, by setting the spectral transmittance curve of the green light in the wavelength selection filter having spectral characteristics to transmit the green light so that the rising half-value wavelength on the short wavelength side is within the range of 490 nm to 500 nm, Good color balance can be achieved.

  In the above embodiment, a Philips type color separation prism is used. However, the present invention is not limited to other color separation prisms such as a cross dichroic type color separation prism or a four-plate type or two-plate type color separation prism. It is applicable.

1 is a schematic configuration diagram showing a color separation optical system according to an embodiment of the present invention. Explanatory drawing which shows the spectral characteristics of the 2nd dichroic film | membrane used for the color separation optical system which concerns on embodiment of this invention Explanatory drawing which shows the spectral transmittance curve of the light absorption layer containing the dichroic film | membrane of red reflection / green transmission, colored glass, and pigment | dye in the conventional color separation optical system

Explanation of symbols

10 Color separation prism 11 Blue separation prism 11a Blue area light exit surface 11b Total reflection prism surface (blue reflection)
12 Red separation prism 12a Red area light exit surface 12b Total reflection prism surface (red reflection)
12c Light emission surface of optical glass 120 Optical glass 121 Coating layer containing pigment 13 Green separation prism 13a Green light emission surface 14B Blue solid-state image pickup device 14R Red solid-state image pickup device 14G Green solid-state image pickup device 15 First dichroic film 16 Second dichroic membrane

Claims (3)

A first prism, a second prism, and a third prism, which are arranged in order from the light incident side, and are arranged on a predetermined prism surface of the prism and selectively transmit light in a predetermined wavelength range; In a color separation optical system including a plurality of wavelength selection filters having different spectral characteristics to be reflected,
Among the wavelength selection filters, a wavelength selection filter that is provided at a boundary surface between the second prism and the third prism and has a spectral characteristic that reflects red range light and transmits green range light has its spectral characteristics. In the transmittance curve, the rising half-value wavelength on the short wavelength side of green light is set in the range of 480 nm to 510 nm, and the wavelength having a transmittance of 15% on the short wavelength side across the rising half-value wavelength A color separation optical system characterized in that a difference from a wavelength having a transmittance of 80% on the long wavelength side is set within 30 nm. A first prism, a second prism, and a third prism, which are arranged in order from the light incident side, and are arranged on a predetermined prism surface of the prism and selectively transmit light in a predetermined wavelength range; In a color separation optical system including a plurality of wavelength selection filters having different spectral characteristics to be reflected,
The wavelength selection filter is provided on a light reflecting surface of the first prism facing the light incident surface of the second prism, and reflects the blue color light and transmits the red color light and the green color light. A wavelength selective filter having:
A wavelength selective filter provided at a boundary surface between the second prism and the third prism, having a spectral characteristic that reflects red light and transmits green light;
The wavelength selective filter having the spectral characteristic of reflecting the red light and transmitting the green light has a rising half-value wavelength on the short wavelength side of the green light within the range of 480 nm to 510 nm in the spectral transmittance curve. The difference between the wavelength having a transmittance of 15% on the short wavelength side and the wavelength having a transmittance of 80% on the long wavelength side is set within 30 nm across the rising half-value wavelength. A color separation optical system. A solid-state image sensor is disposed to face the light exit surfaces of the plurality of prisms,
Among the plurality of prisms, there is no need to be included in the incident light to the solid-state image sensor between the light exit surface and the light-receiving surface of the solid-state image sensor disposed facing the prism that emits red light. color separation optical system according to claim 1 or 2 coating layer comprising a dye having a spectral characteristic for removing light in a wavelength band, characterized in that the thus provided.

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