JP2000221310A - Color separation prism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen the influence on videos by the ghost images specific to a color separation prism arising when adhering the prisms to each other by forming antireflection films on the adhesive surfaces of the prisms to each other of the color separation prism formed by integrating the plural prisms by adhesion. SOLUTION: The prism block 1 which is the color separation prism comprises three pieces of the prisms T1, T2 and T3 and image pickup elements D1, D2 and D3 to be exclusively used for the respective colors R, G and B. The prism block 1 is formed by vapor deposition of one layer or two layers of the antireflection films 5 and 5A to the surfaces S2 and S3 which are the adhesive surfaces of the prisms T1 and T2 to each other. When adhering the prisms to each other by forming the antireflection films 5 and 5A on the surfaces S2 and S3 by vapor deposition in the manner described above, the influence on the videos by the ghost images specific to the color separation prism arising when the increase in the layer thickness of the layers of the adhesive materials is resulted or when the adhesion of the prisms to each other with inclination is resulted may be lessened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for solving a problem peculiar to a color separation prism mainly in a color separation prism used for a video camera.

[0002]

2. Description of the Related Art In a video camera, a color separation prism for separating incident light from an image pickup lens into three primary colors of light (R, G, B) and three image pickup devices (R, G, B) dedicated to each of the separated colors. There is a so-called 3CCD camera system using a prism block composed of a CCD (CCD).

That is, the 3CCD camera system uses a color separation prism to highly accurately convert incident light from an imaging lens into R light.
(Red), G (green), and B (blue) are separated into three colors, and each light is independently captured by three image sensors, so that excellent color reproducibility and high resolution can be obtained.

As shown in FIG. 6, in a prism block a which is a conventional general color separation prism for a video camera, three prisms T1, T2 and T3, R,
It is composed of image pickup devices D1, D2, and D3 dedicated to G and B colors, and the prisms and each prism and each image pickup device are fixed by a transparent adhesive.

It is desirable to use an adhesive having a refractive index relatively close to the refractive index of the prism.
It is also desirable that the thickness of the adhesive layer, that is, the thickness of the adhesive layers b, b be as small as possible.

Although not shown, the prisms T1 and T1
A reflective film having a property of reflecting green light is deposited on a surface S2 bonded to the prism 2 and a property of reflecting blue light on the surface S4 of the surfaces S4 and S5 bonded to the prisms T2 and T3. Is deposited.

The incident light from the image pickup lens enters the inside of the prism block a from the surface S1 of the prism block a, only the green light is reflected on the inner surface of the surface S2, and is totally reflected on the inner surface of the surface S1, and is an image sensor dedicated to green. Reach D1. The remaining blue light and red light reflect the blue light on the inner surface of the surface S4 and transmit the red light, and the blue light and the red light respectively reach the imaging elements D2 and D3 dedicated to each color.

[0008] By the way, with the above-mentioned adhesive,
The individual prisms T1, T2 and T3 are connected to the optical surfaces S2 and S
3, in the prism block a bonded by S4 and S5, for example, the refractive index of the adhesive is 1.55, the refractive index of each prism T1, T2 and T3 is 1.694, and the surface S2
The reflectance at the interface between the adhesive layer and the prism when the light incident angle on the surface and the surface S3 is 25 ° is a graph showing the spectral reflectance in FIG. 7 (horizontal axis: wavelength nm, vertical axis: reflectance%) ), It is about 0.2%.

If the prisms T1 and T2 are in close contact with each other as shown in FIG. 6, about 0.2% of the red light and the blue light transmitted through the surface S2 of the prism T1 are on the inner surface of the surface S3 of the prism T2. The light is reflected, again passes through the surface S2, and reaches the image pickup device D1 for green light. At this time, the blue light and the red light reflected on the inner surface of the surface S3 are aligned with the regular green light and the image forming position. They will match exactly.

[0010] However, as shown in FIG.
When the surface S2 of the prism T2 and the surface S3 of the prism T2 are bonded in an inclined state, the blue light and the red light reflected on the inner surface of the surface S2 or the surface S3 are slightly focused on the regular green light. It will be shifted. Further, the blue light and the red light transmitted through the surface S3 of the prism T2 are respectively dedicated image sensors D2.
And D3. Therefore, the three imaging elements D1, D
When the outputs from D2 and D3 are combined, a green ghost image is generated in the immediate vicinity of the normal image for a high-brightness and minute subject such as a point light source.

This phenomenon is a phenomenon peculiar to the color separation prism block, and the larger the inclination of the bonding surface due to the adhesive layers b, the larger the thickness of the adhesive layers b, b, or the prism. The larger the block a, the greater the separation between the normal image and the ghost image when the output from the image sensor is combined, making the image more conspicuous, and furthermore, the adhesive and the prism T1,
As the difference between the refractive indices of T2 and T3 is larger, the image of the ghost image becomes clearer and more conspicuous.

In order to prevent the above phenomenon, the two adhesive layers b, b between the surface S2 and the surface S3 and between the surface S4 and the surface S5 are extremely thin and parallel to each surface. It is preferable that the refractive index of the adhesive is the same as that of the prism (the inclination of each surface due to the adhesive layer is small) or the refractive index of the adhesive is exactly the same as that of the prism.

However, it is technically difficult to bond the adhesive layers b, b so that the surfaces S2 and S3, and the surfaces S4 and S5, which are the bonding surfaces, are not inclined. It is also difficult to make the refractive index of the material equal to that of each prism because both materials are restricted in design and manufacturing.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and when the prisms are adhered to each other, when the layer pressure of the adhesive layer is increased and when the prisms are inclined and adhered. It is an object of the present invention to reduce the influence on a video image due to a ghost image peculiar to a color separation prism which is generated when the image has been lost.

[0015]

In order to solve the above-mentioned problems, a color separation prism according to the present invention is a color separation prism for integrating incident light from an imaging lens into three primary colors of light, which are formed by bonding a plurality of prisms together. In the decomposing prism, an antireflection film is formed on a bonding surface between the prisms.

Therefore, when the prisms are adhered to each other, the ghost image peculiar to the color separation prism generated when the layer pressure of the adhesive layer is increased and when the prisms are inclined and adhered to each other. It is possible to reduce the influence on the image.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the color separation prism of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 1, a prism block 1, which is a color separation prism for a video camera, includes three prisms T1, T2, and T3 and image pickup devices D1, D2, and D3 dedicated to R, G, and B colors. And the prisms and each prism and each imaging element are fixed with a transparent adhesive.

It is desirable to use an adhesive having a refractive index relatively close to the refractive index of each prism. Further, the adhesive layers 2 and 2 (only the adhesive layer 2 between the surfaces S2 and S3) are used. It is desirable to make the layer thickness as small as possible.

The surface S where the prisms T1 and T2 are bonded is shown.
A dichroic film 3 having a characteristic of reflecting green light is deposited on the surface 2 and a surface S4 on which the prisms T2 and T3 are adhered.
Has a dichroic film 4 having a characteristic of reflecting blue light.
Has been deposited.

The incident light from the imaging lens enters the prism block 1 from the surface S1 of the prism block 1, only the green light is reflected on the inner surface of the surface S2, and is totally reflected on the inner surface of the surface S1, and is an image sensor dedicated to green. Reach D1. The remaining blue light and red light reflect the blue light on the inner surface of the surface S4 and transmit the red light, and the blue light and the red light respectively reach the imaging elements D2 and D3 dedicated to each color.

As described above, when the surface S2 of the prism T1 and the surface S3 of the prism T2 are bonded in an inclined state, the blue light and the red light reflected on the inner surface of the surface S2 or the surface S3 are not reflected. , The image forming position is slightly shifted from the regular green light.

Further, the blue light and the red light transmitted through the surface S3 of the prism T2 are converted into dedicated image pickup devices D2 and D3, respectively.
To reach. Therefore, three image sensors D1, D2 and D
When the outputs from the third and third light sources are combined, a green ghost image is generated in the immediate vicinity of the normal image for a high-brightness and minute subject such as a point light source.

This phenomenon is a phenomenon peculiar to the color separation prism block, and the bonding surfaces S2 and S3 formed by the bonding material layers 2 and 2.
And the larger the inclination of S4 and S5, the more the adhesive layer 2,
As the thickness of the layer 2 is larger, or as the prism block 1 is larger, the separation of the normal image and the ghost image becomes larger when the outputs from the imaging devices D1, D2, and D3 are combined, so that the image becomes more conspicuous. And prism T1, T2 and T
As the difference between the refractive index of the ghost image and that of the ghost image becomes larger, the image of the ghost image becomes clearer and more conspicuous.

Therefore, in order to prevent the above phenomenon, the two adhesive layers 2, 2 between the surfaces S2 and S3 and between the surfaces S4 and S5 are extremely thin and parallel to each surface ( It is desirable that the inclination of each surface due to the adhesive layer is small) or that the refractive index of the adhesive is exactly the same as the refractive index of the prism.

However, it is technically difficult to bond the adhesive layers 2 and 2 thinly so that the surfaces S2 and S3 and S4 and S5, which are the bonding surfaces, are not inclined. It is also difficult to make the refractive index of the material the same as the refractive index of each prism because both materials are restricted in design and manufacturing.

Therefore, in the prism block 1, one or two layers of an antireflection film are formed on the bonding surfaces of the prisms by vapor deposition, and a surface of the prism block 1 other than the bonding surface has a specific color. The dichroic films 3 and 4 having the property of selectively transmitting only light and reflecting other light are formed by vapor deposition. Less than,
The details will be specifically described.

When the refractive index of the adhesive is 1.55 and the refractive index of the prism is significantly different from 1.694, the reflectance at the interface between the adhesive layer and the prism is about 0, as shown in FIG. .2%.

By forming the anti-reflection film 5 on the surface S3 by vapor deposition as shown in FIG. 1, the brightness of the ghost image can be reduced.

In the case of the prism and the adhesive having the refractive indexes of 1.55 and 1.694, respectively, as the deposition material for forming the antireflection film 5, aluminum oxide (Al ₂₎ having the refractive index of 1.62 is used. By selecting O ₃ ),
As shown in (2), it is possible to make the reflectance on the inner surface of the surface S3 close to 0, and as a result, the brightness of the ghost image is reduced. Aluminum oxide is widely used as a deposition material for applications such as antireflection of optical glass.

In addition, in addition to aluminum oxide, the reflectance of the inner surface of the surface S3 is set to 0 due to the relationship between the refractive index of the prism and the adhesive as described above in addition to aluminum oxide. Any substance can be used as long as it has a refractive index that allows it to be brought closer.

Next, when the refractive index of the adhesive is 1.55 and the refractive index of the prism is 1.591, and the difference between the two is small, if the adhesive layers 2, 2 and the prism are As shown in FIG. 3, the reflectivity at the interface is a sufficiently small value of about 0.02%. Means for further reducing this will be described.

That is, as shown in FIG. 1, the antireflection film on the surface S3 of the prism block 1 has a single-layer structure of aluminum oxide in the above-described example, but has a layer of silicon dioxide (SiO ₂ ). The antireflection film 5A has a two-layer structure with an aluminum oxide layer. Silicon dioxide, like aluminum oxide, is also a common deposition material used for optical glass.

By appropriately setting the film pressure of each layer made of aluminum oxide and silicon dioxide of the antireflection film 5A, the reflectance on the inner surface of the surface S3 is reduced, and as a result, the brightness of the ghost image is reduced. Weakens. In this example,
As shown in FIG. 4, the reflectance on the inner surface of the surface S3 is further reduced to substantially 0%.

The deposition material constituting the antireflection film 5A having the two-layer structure is, for example, a combination of magnesium fluoride (MgF ₂ ) and aluminum oxide, and magnesium fluoride in addition to silicon dioxide and aluminum oxide. Like the combination of zirconium oxide (ZrO ₂ ), the surface S3
Any substance may be used as long as it has a combination of a refractive index that enables the reflectance of the surface S3 to approach 0, and the reflectance on the inner surface of the surface S3 is not limited to the two-layer structure, and can be approximated to 0. If so, a structure having two or more layers may be used.

When the prisms T2 and T3 are bonded to each other, if the surfaces S4 and S5 are bonded at an angle or if the adhesive layer 2 between them becomes thick, the image pickup device D2 for blue light is used. A red ghost image is formed on the prism T3, and a blue ghost image is generated. Similarly, when the antireflection film 5 or 5A is formed on the surface S5 of the prism T3, similarly to the surface S3, the ghost image of the ghost image is formed. The brightness can be reduced.

As shown in FIG. 8, a ghost image is generated by forming blue light and red light on the image pickup device D1 for green light, and therefore, after being reflected by the inner surface of the surface S2 or the surface S3. By depositing a dichroic film having a property of selectively reflecting only red light and blue light on any surface while reaching the image pickup device D1 for green light,
It is apparent that the generation of the ghost image can be suppressed.

That is, as shown in FIG. 5, a dichroic film 6 having a property of transmitting green light and selectively reflecting red light and green light is formed on the exit surface SG which is the exit surface of the prism T1 by vapor deposition. ing.

Therefore, for example, even when the surfaces S2 and S3 are bonded at an angle as shown in the figure, the green light reflected on the inner surface of the surface S2 is totally reflected on the surface S1 and transmitted through the exit surface SG. An image is formed as a regular image on the image sensor D1 for green light.
A part of the blue light and the red light is reflected by the surface S3 and travels as a ghost component to the green light imaging device D2, but is reflected by the emission surface SG and does not reach the green light imaging device. No image is generated.

The surface on which the dichroic film 6 is formed by vapor deposition may be other than the above-mentioned emission surface SG, for example, the surface of the image pickup device D1 for green light.

On the other hand, the adhesive layer 2 for adhering the surfaces S4 and S5 has a certain thickness, or the surfaces S4 and S5
The ghost image resulting from the inclination of the prism T2 is, similarly to the above, the exit surface of the prism T2 or the image sensor D2 for blue light.
By forming a dichroic film having such a property that blue light is transmitted and red light is reflected on the surface or the like, the generation can be prevented.

As described above, according to the present invention, by forming an anti-reflection film or a dichroic film on a prism surface or a surface of an image pickup device by vapor deposition, the thickness of the adhesive material layer in the production of the prism block becomes large, An object of the present invention is to solve the problem of a ghost image generated when an adhesive surface is inclined by an adhesive layer. Also,
As a derivative effect, there is no need for a manufacturing means for preventing the surface to which the prism is bonded from being tilted, and it is also unnecessary to inspect the tilt of the surface to be bonded and the ghost image. Furthermore, by providing the anti-reflection film, the refractive index of the adhesive and the refractive index of the prism do not always have to be close to each other, so that the range of selection of the adhesive and the material of the prism is expanded,
Design flexibility is improved.

It should be noted that the specific shapes and structures of the respective parts shown in the above-described embodiment are merely examples for embodying the present invention, and the technical features of the present invention will be described below. The scope should not be construed as limiting.

[0044]

As is clear from the above description, the color separation prism of the present invention converts the incident light from the image pickup lens into three light beams by integrating a plurality of prisms by bonding.
In the color separation prism that separates into primary colors, an anti-reflection film is formed on the bonding surface between the prisms, so that the reflectance on the bonding surface between the prisms becomes small, and when bonding the prisms, the layer of the adhesive material layer is formed. It is possible to reduce the influence on the image due to the ghost image peculiar to the color separation prism, which occurs when the pressure is increased and when the prisms are inclined and adhered to each other.

According to the second aspect of the present invention, since the antireflection film has a two-layer structure, the reflectance of the bonding surface between the prisms can be made extremely small.

Further, according to the invention described in claims 3 and 4, after color separation, only light of a specific color is selected on a surface other than the bonding surface between the prisms on which the antireflection film is formed. Since the dichroic film having the property of transmitting light and reflecting light of a color other than the specific color light is formed, the reflectance on the bonding surface of the prisms is reduced, and when bonding the prisms, an adhesive material is used. In this case, it is possible to effectively prevent the occurrence of a ghost image peculiar to the color separation prism, which is generated when the layer pressure of the layer is increased and when the prisms are inclined and adhered to each other.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the color separation prism of the present invention together with FIG. 2 to FIG. 5, and FIG. 1 is a view schematically showing the whole.

FIG. 2 is a graph showing a spectral reflectance of the color separation prism shown in FIG.

FIG. 3 shows that the reflectance of the adhesive and the prism is 1.
It is a graph which shows the spectral reflectance at 55 and 1.591.

FIG. 4 is a graph showing the spectral reflectance when the antireflection film has a two-layer structure.

FIG. 5 is a diagram schematically showing an entire modification of the color separation prism shown in FIG. 1;

FIG. 6 together with FIGS. 7 and 8 show the problems of the conventional color separation prism, and this figure is a diagram schematically showing the basic principle of the color separation prism.

7 is a graph showing the spectral reflectance of the color separation prism shown in FIG.

FIG. 8 is a diagram schematically illustrating a problem of a color separation prism.

[Explanation of symbols]

Reference Signs List 1: color separation prism, T1: prism, T2: prism, T3: prism, 5: anti-reflection film, 5A: anti-reflection film, 6: dichroic film, S3: surface, SG: surface

Claims (4)

[Claims] 1. A color separation prism which integrates a plurality of prisms by bonding and separates incident light from an imaging lens into three primary colors of light, wherein an anti-reflection film is formed on a bonding surface between the prisms. Characteristic color separation prism. 2. The color separation prism according to claim 1, wherein the antireflection film has a two-layer structure. 3. After color separation, only light of a specific color is selectively transmitted to a surface other than the adhesive surface between the prisms on which the antireflection film is formed, and light of a color other than the light of the specific color is reflected. 2. The color separation prism according to claim 1, wherein a dichroic film having characteristics to cause the color separation is formed. 4. After color separation, only light of a specific color is selectively transmitted to a surface other than the adhesive surface between the prisms on which the antireflection film is formed, and light of a color other than the light of the specific color is reflected. 3. The color separation prism according to claim 2, wherein a dichroic film having a property to cause the color separation is formed.