JP2023056651A - Color separation optical system and imaging apparatus - Google Patents

Abstract

To prevent the occurrence of image blur and ghost resulting from dew condensation generated in a gap between optical elements.SOLUTION: A color separation optical system 1 has a first optical element CP1 having a first incident surface 2 and a first reflection surface 3 provided with a first dichroic film that reflects part of light from the first incident surface and transmits the rest of the light, and a second optical element CP2 having a second incident surface 6 that is opposite to the first reflection surface with a gap therebetween. Between the first reflection surface and the second incident surface, when an area through which effective light for forming a subject image on an image pick-up device 11R passes is defined as a first area A1, an area outside the first area as a second area A2, and an area outside the second area as a third area A3, the second area is provided with a light-shielding part 14 that surrounds the whole circumference of the first area and separates the first area and the third area from each other.SELECTED DRAWING: Figure 6

Description

The present invention relates to a color separation optical system used in imaging devices such as television cameras and video cameras.

As the color separation optical system as described above, there is used one that divides incident light into three colored lights of blue light, green light and red light, and guides these colored lights to imaging devices for respective colored lights. Patent Document 1 discloses a first prism having a first incident surface and a reflecting surface (dichroic film) that reflects part of the light from the first incident surface and transmits the rest of the light, and an air gap with respect to the reflecting surface. A color separation optical system is disclosed having a second prism having a second entrance surface facing the spaced apart. Further, Japanese Patent Laid-Open No. 2002-200002 discloses a configuration for suppressing the astigmatic difference by controlling the air gap between the first and second prisms to be thin.

Japanese Patent No. 5484258 JP 2004-191878 A

However, when an air gap is provided between the first and second prisms, dew condensation occurs on the prism surfaces (the first reflecting surface and the second entrance surface) that are in contact with the air gap when the environmental temperature suddenly drops. When moisture generated by such dew condensation enters an effective area through which light forming an object image passes on the imaging device, an optical image formed on the imaging device is blurred. In addition, due to fluctuations in the refractive index in the air gap due to moisture, transmission and reflection beyond the design occur after the second prism, and as a result, unnecessary light (ghost) is generated. Patent Documents 1 and 2 do not disclose a configuration for suppressing such dew condensation.

SUMMARY OF THE INVENTION The present invention provides a color separation optical system and an imaging apparatus using the same that can suppress the occurrence of image blurring and ghosts caused by dew condensation occurring in air gaps provided between prisms (optical elements).

A color separation optical system as one aspect of the present invention separates light incident from a subject into a plurality of colored lights having different wavelengths, and guides the plurality of colored lights to an imaging device. The color separation optical system includes a first optical element having a first reflecting surface provided with a first incident surface and a first dichroic film that reflects part of the light from the first incident surface and transmits the rest of the light. and a second optical element having a second incident surface facing the first reflecting surface with a gap therebetween. An area between the first reflecting surface and the second incident surface through which effective light forming a subject image on the imaging device passes is a first area; an area outside the first area is a second area; When the outer area is defined as the third area, the second area is provided with a light shielding portion that surrounds the entire circumference of the first area and separates the first area from the third area. An imaging apparatus using the color separation optical system also constitutes another aspect of the present invention.

According to the present invention, it is possible to suppress the occurrence of image blur and ghost caused by dew condensation occurring in the air gap provided between the first and second optical elements in the color separation optical system.

FIG. 2 is a diagram showing the color separation optical system of Example 1; 4 is a diagram showing the spectral transmittance of the color separation optical system of Example 1. FIG. 4A and 4B are diagrams showing transmission characteristics of a dichroic film in the color separation optical system of Example 1. FIG. 4 is a diagram showing optical paths of effective light in the color separation optical system of Example 1. FIG. 4A and 4B are diagrams showing optical paths of ghost light in Embodiment 1. FIG. FIG. 10 is a diagram showing ghost countermeasures in the first embodiment; 4A and 4B are diagrams showing a method of controlling an air gap in the first embodiment; FIG. FIG. 8 is a diagram showing a method of controlling an air gap in Example 2; FIG. 10 is a diagram showing another air gap control method in the second embodiment; FIG. 10 is a diagram showing optical paths of ghost light in Example 3; FIG. 11 is a diagram showing ghost countermeasures in the third embodiment; FIG. 11 is a diagram showing a color separation optical system of Example 4;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG. 1 shows the configuration of an imaging apparatus including a color separation optical system 1 that is Embodiment 1 of the present invention. The imaging apparatus has an objective lens (objective optical system) 20 that forms an image of light from a subject, and a color separation optical system 1 that receives the light passing through the objective lens 20 . Imaging devices are used as video cameras, endoscopes, industrial cameras, and the like. The objective lens 20 may be provided integrally with the imaging device, or may be detachable (replaceable) from the imaging device.

The color separation optical system 1 separates the light from the objective lens 20 into three color lights of blue (B), green (G) and red (R), which are captured by image sensors 11B, 11G and 11R for respective color lights. A subject image (optical image) formed by each color light is picked up. The imaging elements 11B, 11G, and 11R are photoelectric conversion elements such as CCD sensors and CMOS sensors, and convert subject images into electrical signals.

In the following description, the imaging elements 11B, 11G, and 11R are collectively referred to as an imaging element 11 as well. Further, in this embodiment, a plurality of (three) colored lights having different wavelengths are separated into blue light as the first colored light, red light as the second colored light, and green light as the third colored light. By way of example, the first through third colored lights may be any of blue, red and green light, or may be other colored lights.

The color separation optical system 1 includes a first prism (first optical element) CP1 for blue separation, and an air gap 5 between the first prism CP1 and the first prism CP1 for blue separation, in this order in the direction in which light from the objective lens 20 travels. and a second prism (second optical element CP2) for red separation. Furthermore, the color separation optical system 1 has a third prism CP3 in contact with (bonded to) the second prism CP2. All materials of the first to third prisms CP1 to CP3 have the same refractive index.

The first prism CP1 has a first entrance surface 2, a first reflection surface 3 in contact with the air gap 5, and a first exit surface 4 facing the blue light imaging element 11B. Light from the objective lens 20 passes through the first incident surface 2, enters the first prism CP1, and travels toward the first reflecting surface 3. As shown in FIG. The first reflecting surface 3 is provided with a blue-reflecting dichroic film (first dichroic film) that reflects only blue light and transmits the remaining green and red light. A blue-reflecting dichroic film is composed of a dielectric multilayer film. The blue light reflected by the first reflecting surface 3 is totally internally reflected by the first entrance surface 2, passes through the first exit surface 4, is emitted from the first prism CP1, and enters the imaging element 11B.

The second prism CP2 has a second incident surface 6 in contact with the air gap 5 (facing the first reflecting surface 3 with the air gap 5 therebetween), and a second reflecting surface 7 to which the third prism CP3 is adhered. , and a second emission surface 8 facing the imaging element 11R for red light. The green light and red light transmitted through the first reflecting surface (blue reflecting dichroic film) 3 enter the second prism CP2 through the second incident surface 6 . A multilayer antireflection film is provided on the second incident surface 6 . The second reflecting surface 7 is provided with a red reflecting dichroic film (second dichroic film) that reflects only red light and transmits the remaining green light. The red reflective dichroic film is composed of a dielectric multilayer film. The red light reflected by the second reflecting surface 7 is totally internally reflected by the second entrance surface 6, passes through the second exit surface 8, is emitted from the second prism CP2, and enters the imaging element 11R.

The third prism CP3 has a third entrance surface 9 adhered to the second reflecting surface 7, and a third exit surface 10 facing the green light imaging element 11G. The green light that has passed through the second reflecting surface (red reflecting dichroic film) 7 passes through the third incident surface 9, enters the third prism CP3, passes through the third exit surface 10, and exits the third prism CP3. It exits and enters the imaging device 11G.

FIG. 2 shows spectral transmission characteristics of the entire color separation optical system 1. As shown in FIG. The dotted line indicates the transmittance for blue light, the solid line indicates the transmittance for green light, and the dashed-dotted line indicates the transmittance for red light. 3(a) and 3(b) respectively show the spectral transmittance (solid line) and the spectral reflectance (dotted line) of the blue-reflecting dichroic film and the red-reflecting dichroic film for obtaining the spectral transmittance characteristics shown in FIG. ing.

In this embodiment, the red-reflecting dichroic film is composed of a multi-layer film having a red light transmittance of 0.5% or less. As a result, good spectral transmission characteristics as shown in FIG. 2 are obtained.

Further, in this embodiment, the red-reflecting dichroic film is constructed using a dielectric multilayer film in which high refractive index layers and low refractive index layers are alternately arranged. Among such dielectric multilayer films, there is one in which a high refractive index layer is composed of TiO ₂ , ZrO ₂ , ZnS or the like, and a low refractive index layer is composed of SiO ₂ , MgF ₂ , Al ₂ O ₂ or the like. In the present example, alternating layers of TiO ₂ and SiO ₂ with a basic film thickness of 1:1 are used to obtain the characteristics shown in FIG. 3(b).

FIG. 4 shows rays of light that enter the color separation optical system 1 from the objective lens 20 and pass through the first prism CP1 and the second prism CP2 and reach the red light imaging device 11R. A ray D indicates a marginal ray that passes through the lowest position in the drawing among the off-axis rays that enter the image sensor 11R.

In order to totally reflect the light ray D on the second incident surface 6 in the second prism CP2,
θ2>(θ1+δ+θmax)/2 (1)
must satisfy the following conditions.

In equation (1), θ1 is the apex angle of the first prism CP1 (the angle between the first incident surface 2 and the first reflecting surface 3), θ2 is the apex angle of the second prism CP2 (the second incident surface 6 and the 2 angle formed by the reflecting surface 7). Also, let n be the refractive index of the material of the first and second prisms CP1 and CP2, and Fno be the F number of the objective lens 20,
θmax=sin ⁻¹ {1/(2·n·Fno)}
δ=sin ^-1 (1/n)
is.

Next, the occurrence of image blurring and ghosting in the color separation optical system 1 will be described. As described above, when the air gap 5 is provided between the first reflecting surface 3 of the first prism CP1 and the second incident surface 6 of the second prism CP2, if the environmental temperature of the imaging device suddenly drops, , dew condensation occurs on the first reflecting surface 3 and the second incident surface 6 which are prism surfaces in contact with the air gap 5 . In particular, since the temperature drops more in the periphery near the outer surfaces of the first and second prisms CP1 and CP2 (surfaces perpendicular to the entrance surface, reflection surface, and exit surface of each prism where light does not enter), dew condensation occurs. It tends to occur around the first reflecting surface 3 and the second incident surface 6 .

Then, when moisture generated by dew condensation enters an effective area between the first reflecting surface 3 and the second incident surface 6, which is an area through which effective light forming a subject image passes through the image sensor 11R, the image sensor The subject images formed on 11R and 11G are blurred.

Moreover, the surface (image pickup surface) of a general image pickup device is provided with a metal coating, and the reflectance thereof is relatively high. Therefore, part of the red light color-separated by the second prism CP2 may be reflected on the surface of the imaging element 11R and directed toward the second incident surface 6. FIG. At this time, as shown in FIG. 5, if a substance (moisture in this case) having a refractive index different from that of air exists in the effective area, the red light is reflected on the surface of the imaging element 11R and travels toward the second incident surface 6. may be transmitted through the second entrance surface 6 without satisfying the total reflection condition. The red light that has passed through the second incident surface 6 passes through the substance 12 and the first reflecting surface 3, enters the first prism CP1, is reflected by the first incident surface 2, and reaches the imaging element 11B. As a result, a ghost occurs on the image sensor 11B.

In order to suppress the occurrence of such image blurring and ghosting, in this embodiment, a light blocking portion 14 shown in FIG. 6 is provided. The left side of FIG. 6 shows the entire color separation optical system 1, and the right side shows the second prism CP2 viewed from the second incident surface 6 side. As shown in the diagram on the right side, the light shielding portion 14 has an effective area (second area) A2 outside the effective area (first area) A1 between the first reflecting surface 3 and the second incident surface 6. It is provided so as to surround the entire circumference of A1. The light-shielding portion 14 is formed of a light-shielding material such as a sheet material having elasticity or paint having adhesiveness to the prism surface. Screen printing, a dispenser, or the like is used to apply the paint.

Unlike the substance 12 described above, the light shielding part 14 not only has a property of not transmitting light, but also has a peripheral area (third area) A3 outside the effective area A1 and the area A2 where the light shielding part 14 is provided. have the role of spatially separating the The peripheral area A3 is an area corresponding to the peripheral portion near the outer side surfaces of the first and second prisms CP1 and CP2 where dew condensation is likely to occur as described above. By adopting such a configuration, it is possible to prevent moisture generated due to dew condensation in the peripheral portions near the outer surfaces of the first and second prisms CP1 and CP2 from entering the effective area A1. It is possible to suppress the occurrence of blurring and ghosting.

It is preferable that the transmittance of the light shielding portion 14 is close to 0%, but the transmittance should be 10% or less. Further, the light shielding portion 14 has a contact area with respect to the first reflecting surface 3 and the second incident surface 6 to prevent moisture generated in the peripheral area A3 from flowing into the effective area A1.

Moreover, if the thickness of the air gap 5 increases, the astigmatic difference increases and the imaging performance may deteriorate. In the above-mentioned Patent Document 2, the vapor-deposited film is used as a spacer to control the thickness of the air gap to 5 μm. However, the vapor deposition film has low adhesion to either one of the prism surfaces that are in contact with the air gap, or cannot be formed so as to continuously surround the outer periphery of the effective area. intrusion into the effective area of Also, the use of vapor deposition increases manufacturing costs. Therefore, it is desirable to use a sheet material or paint as the light shielding material forming the light shielding portion 14 as in this embodiment.

Further, in this embodiment, as shown in FIG. 7, the adhesive containing the filler is applied to a portion (three places in the drawing) of the portions in contact with the peripheral area A3 of the first reflecting surface 3 and the second incident surface 6. It is As a result, three bonding portions 15 are provided in the peripheral area A3 to bond the first prism CP1 and the second prism CP2 with an air gap 5 therebetween. The particle size (average particle size) of the filler is preferably 6 μm or less. Furthermore, it is preferable that the particle size of the filler be 4 μm or more and 6 μm. With this configuration, the thickness of the air gap 5 can be maintained at the particle size of the filler. The thickness of the light shielding portion 14 may be changed according to the thickness of the air gap 5 determined by the particle size of the filler.

According to this embodiment, it is possible to suppress the occurrence of image blurring and ghost caused by dew condensation caused by providing the air gap 5 in the color separation optical system 1 .

Next, Example 2 of the present invention will be described. The basic configuration of the color separation optical system in this embodiment is the same as in the first embodiment.

FIG. 8(a) shows the second prism CP2 viewed from the side of the second incident surface 6 in the color separation optical system of this embodiment. Also in this embodiment, the light shielding portion 14 is provided in the area A2 surrounding the outside of the effective area A1.

Here, the angle of incidence of light incident on the first reflecting surface 3 (the angle formed with respect to the normal to the first reflecting surface 3) of the two directions perpendicular to the normal to the first reflecting surface 3 and perpendicular to each other A direction with a large incident angle is defined as a first direction, and a direction with a small incident angle is defined as a second direction. The first direction is the direction in which the length of the effective area A1 is longer than the second direction, and corresponds to the vertical direction (actually the horizontal direction) in the figure. The second direction is a direction in which the length of the effective area A1 is shorter than that in the first direction, and corresponds to the left-right direction (actually the vertical direction) in the figure. At this time, two adhesive portions 15 extending to the entire peripheral area A3 in the first direction are provided on both sides of the effective area A1 in the second direction in the peripheral area A3. As a result, the bonding area becomes wider than that of the first embodiment, and the bonding strength between the first prism CP1 and the second prism CP2 can be increased.

Further, as shown in FIG. 8B, in addition to the two bonding portions 15 shown in FIG. good. Thereby, the bonding strength can be further increased.

8(a) and 8(b), as well as FIG. 7 of the first embodiment, the adhesive portion 15 is located on one side of both sides of the effective area A1 in the first direction in the peripheral area A3 (lower side in each figure). side). This will be described later in Example 3 with reference to FIG. 10, but the portion of the second incident surface 6 of the second prism CP2 that is in contact with the lower portion of the peripheral area A3 has light outside the effective area A1. may enter. This is because if an adhesive portion is provided in the lower portion of the peripheral area A3, this light will pass through the second incident surface 6 and enter the first prism CP1 to become ghost light.

Further, as shown in FIG. 9, a spacer (not shown) is sandwiched between the first reflecting surface 3 and the second incident surface 6 at a portion in contact with the peripheral area A3, and after coating the paint for forming the light shielding portion 14 with a dispenser, A bonding portion 16 may be provided for bonding the outer surfaces of the first and second prisms CP1 and CP2. In this case, the thickness of the air gap 5 is maintained even if the spacer is pulled out after the adhesive portion 16 is cured.

Further, the thickness of the air gap 5 may be ensured by the thickness of the light shielding portion 14 without providing the adhesive portion containing the filler.

Next, Example 3 of the present invention will be described. FIG. 10 shows ghost light different from the ghost light described in FIG. The basic configuration of the color separation optical system is the same as that of the first embodiment.

As described above, when the environmental temperature of the image pickup apparatus drops, the temperature drop is particularly large in the peripheral area A3, so dew condensation is likely to occur on the prism surface in contact with the peripheral area A3. At this time, as shown in FIG. 10, a substance (moisture here) 13 may exist in the lower portion of the peripheral area A3. In this case, of the red light color-separated by the second prism CP2, the light reflected by the surface of the imaging device 11R is not totally reflected by the second incident surface 6 but is transmitted therethrough, and the substance 13 and the first reflecting surface 3 are reflected. , is reflected by the first incident surface 2, and reaches the imaging device 11B. This light becomes ghost light, and a ghost occurs on the image sensor 11B.

Since this ghost light does not pass through the effective area A1, it does not cause image blurring. Light passing through is also recognized as ghost light. In particular, the ghost light that has passed through the lower portion of the peripheral area A3 is incident on the first incident surface 2 at a large incident angle in the first direction. It becomes easy to be recognized by the element 11B.

In order to suppress the occurrence of such ghost light, in this embodiment, as shown in FIG. 11, at least one side (here, the lower A light shielding portion 14 is provided in the portion of the side). In other words, in addition to the area 2, the light shielding part 14 is also provided in the lower part of the peripheral area A3. In this way, by providing the light shielding portion 14 also in the portion of the peripheral area A3 on the side through which the ghost light easily passes among both sides of the effective area A1 in the first direction, the generation of the ghost on the imaging element 11B is suppressed. be able to.

Note that the light shielding portions 14 may be provided on both sides (lower side and upper side) of the effective area A1 in the first direction in the peripheral area A3.

FIG. 12 shows a color separation optical system 101 that is Embodiment 4 of the present invention. The color separation optical system 101 includes a first prism CP101 for blue separation and a red separation prism CP101 arranged with an air gap 105 in order in the traveling direction of light from an objective lens (not shown). and a second prism CP102 for Further, the color separation optical system 101 has a third prism CP103 for yellow separation that is in contact with (bonded to) the second prism CP102, and a fourth prism CP104 that is in contact with the third prism CP103. All materials of the first to fourth prisms CP1 to CP4 have the same refractive index.

The first prism CP101 has a first entrance surface 102, a first reflection surface 103 in contact with the air gap 105, and a first exit surface 104 facing the blue light imaging element 111B. Light from the objective lens passes through the first incident surface 102, enters the first prism CP101, and travels toward the first reflecting surface 103. As shown in FIG. A blue-reflecting dichroic film is provided on the first reflecting surface 103 . The blue light reflected by the first reflecting surface 103 is totally internally reflected by the first entrance surface 102, passes through the first exit surface 104, is emitted from the first prism CP101, and enters the image sensor 111B.

The second prism CP102 has a second entrance surface 106 in contact with the air gap 105, a second reflection surface 107 to which the third prism CP103 is adhered, and a second exit surface 108 facing the red light imaging element 111R. have. Yellow light, green light and red light that have passed through the first reflecting surface (blue reflecting dichroic film) 103 enter the second prism CP102 through the second incident surface 106 . A multilayer antireflection film is provided on the second incident surface 106 . Also, the second reflecting surface 107 is provided with a red reflecting dichroic film. The red light reflected by the second reflecting surface 107 is totally internally reflected by the second entrance surface 106, passes through the second exit surface 108, is emitted from the second prism CP102, and enters the imaging element 111R.

The third prism CP103 has a third incident surface 109 adhered to the second reflecting surface 107, a third reflecting surface 112 adhered to the fourth prism CP104, and a third emitting surface facing the image sensor 111Y for yellow light. a surface 113; The yellow light and green light transmitted through the second reflecting surface (red reflecting dichroic film) 107 enter the third prism CP103 through the third incident surface 109 . A yellow reflective dichroic film is provided on the third reflecting surface 112 . The yellow light reflected by the third reflecting surface 112 passes through the third emitting surface 113, exits from the third prism CP103, and enters the imaging element 111Y.

The fourth prism CP4 has a fourth entrance surface 114 adhered to the third reflecting surface 112, and a fourth exit surface 110 facing the green light imaging element 111G. The green light transmitted through the third reflecting surface (yellow reflecting dichroic film) 112 passes through the fourth incident surface 114, enters the fourth prism CP104, passes through the fourth exit surface 110, and exits the fourth prism CP4. It exits and enters the imaging element 111G.

In this embodiment, as in the first to third embodiments, the light shielding portion 140 is provided in the area surrounding the effective area in the air gap 105 between the first and second prisms CP101 and CP102. This suppresses the occurrence of image blurring and ghosting due to dew condensation caused by providing the air gap 105 .
Each embodiment described above is merely a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

1,101 Color Separation Optical System CP1 First Prism 2 First Incidence Surface 3 First Reflecting Surface 5 Air Gap CP2 Second Prism 6 Second Incident Surface 7 Second Reflecting Surface 11B, 11R, 11G Imaging Device 14 Light Blocking Material 15 , 16 adhesive

Claims (8)

A color separation optical system that separates light incident from a subject into a plurality of colored lights having different wavelengths and guides the plurality of colored lights to an imaging device,
a first optical element having a first reflecting surface provided with a first incident surface and a first dichroic film that reflects part of the light from the first incident surface and transmits the rest;
a second optical element having a second incident surface facing the first reflecting surface with a gap therebetween;
An area between the first reflecting surface and the second incident surface through which effective light forming a subject image on the imaging element passes is a first area, an area outside the first area is a second area, and the second area is an area outside the first area. When the area outside the second area is the third area,
A color separation optical system, wherein the second area is provided with a light-shielding portion that surrounds the entire circumference of the first area and separates the first area from the third area. 2. The color separation optical system according to claim 1, wherein said light shielding portion has a transmittance of 10% or less for light incident on said light shielding portion. Of the two directions orthogonal to the normal to the first reflecting surface and orthogonal to each other, the direction in which the incident light to the first reflecting surface has a large incident angle is defined as a first direction, and the direction in which the incident angle is small is defined as a second direction. When the direction is
3. The color separation according to claim 1, wherein the light shielding portion is provided on at least one of both sides of the first region in the first direction in the third region. Optical system. At least part of the third region is provided with a bonding portion for bonding the first and second optical elements,
4. The color separation optical system according to any one of claims 1 to 3, wherein the adhesive portion contains a filler for holding the gap. 5. A color separation optical system according to claim 4, wherein the particle size of said filler is 4 [mu]m or more and 6 [mu]m or less. Of the two directions perpendicular to the normal to the first reflecting surface and perpendicular to each other, the direction in which the incident light to the first reflecting surface has a large incident angle is defined as a first direction, and the direction in which the incident angle is small is defined as a second direction. When the direction is
6. The adhesive part according to claim 4, wherein the adhesive portion is provided in a portion of the third region excluding a portion on one side of both sides of the first region in the first direction. color separation optical system. 7. The method according to any one of claims 1 to 6, wherein an adhesive portion for bonding the first and second optical elements is provided on an outer surface of the first and second optical elements on which light does not enter. The color separation optical system described in . a color separation optical system according to any one of claims 1 to 7;
and an objective optical system for causing light from a subject to enter the color separation optical system.

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