JP2001159705A - Color separation optical system and television camera using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make increasable Fno because brighter light fluxes are required to pass through a prism. SOLUTION: The color separation optical system is built in a television camera device of high resolution having more than 625 scanning lines, and is disposed between an objective lens and a solid state image pickup device. The system consists of three prisms of first prism, second prism and third prism from the objective lens side and separates three colors. Each of the first and second prisms has three faces of entrance face, exiting face and transmitting face and are disposed facing each other through an air layer. The color separation prisms have an ability to pass the light fluxes from the objective lens of F1.4. The refractive index of each three prisms is smaller than 1.6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color separation optical system used for a high-resolution broadcast television camera exceeding the conventional number of scanning lines of 625 (PAL system), and a television camera using the same. .

[0002]

2. Description of the Related Art Conventionally, in an image pickup apparatus such as a color television camera, after a light from an objective lens is separated into three color lights of blue, green and red by a color separation prism, a subject image based on each color light is separated. , On the corresponding solid-state imaging element surface.

FIG. 4 is a sectional view of a main part of such a conventional color television camera. In the figure, Ca is a camera housing, and Le is an objective lens. The objective lens Le is interchangeable with a mount part MT for connection to the camera housing Ca, and is connected to the camera housing Ca with the flange surface F aligned. The objective lens Le collects a light beam from a subject (not shown) and guides the light beam to a color separation prism.

[0004] The first prism of the color separation prism 1001 reflects only the blue light on the blue reflection dichroic film applied to the transmission surface 1003, and transmits the rest of the light from the objective lens Le incident from the entrance surface 1002. The reflected blue light is totally reflected on the incident surface 1002 and
4 to the solid-state imaging device 1011B.

[0005] The light transmitted through the transmitting surface 1003 of the first prism passes through the air gap 1005 and enters from the incident surface 1006 of the second prism. Transmission surface 1007 of second prism
The red-reflective dichroic film applied to only reflects the red light and transmits the remaining green light. The reflected red light is incident on the entrance surface 1006 of the second prism in contact with the air gap 1005.
The light is totally reflected by the surface, exits the emission surface 1008, and travels toward the solid-state imaging device 1011R.

The green light transmitted through the transmission surface 1007 of the second prism exits the emission surface 1010 and is
Head to 11G. Thus, the color separation prism separates the light beam.

[0007] The shape of the prism system is disclosed in Japanese Patent Application Laid-Open No. 60-427.
As described in Japanese Patent Publication No. 01-2001 or the like, it is determined by the specifications such as the refractive index n and Fno of the glass (glass) material of the prism used. That is, as shown in FIG. 4, the angle between the light incident surface (1002) of the first prism and the dichroic film surface (1003) of the transmitting surface is θ1, the light incident surface (1006) of the second prism and the transmitting surface Dichroic membrane surface (10
07) and θ2, the following conditional expression must be satisfied.

[0008] θ1 ≦ Sin ⁻¹ (1 / n) −Sin ⁻¹ ｛1 / (2n · Fno)｝ (1) 2 · θ1 ≧ Sin ⁻¹ (1 / n) + Sin ⁻¹ ｛1 / ( 2n · Fno)｝… (2) 2 · θ2 ≧ θ1 + Sin ^-1 (1 / n) + Sin ^-1 ｛1 / (2n · Fno)｝… (3) However, conditional expression (1) is dichroic. Conditional expression (2) is that the wavelength region light to be transmitted by the surface 1003 is not totally reflected. Conditional expression (2) is that the wavelength region light reflected by the dichroic surface 1003 is totally reflected by the incident surface 1002. Conditional expression (3) is This is necessary for the wavelength region light reflected on the surface 1007 to be totally reflected on the incident surface 1006.

Here, focusing on the angle θ1, the range in which the angle θ1 can exist is determined from the refractive index of the glass material and Fno from the conditional expressions (1) and (2).

The graph of FIG. 5 illustrates this matter.
Using the refractive index n of the glass material as a parameter, Fno and the angle θ1
The relationship is shown. For example, A of the graph of n = 1.5 is the graph of the condition (1), and B is the graph of the condition (2). From this graph, equations (1),
It can be seen that the range of the angle θ1 that simultaneously satisfies (2) is limited to a range where Fno is substantially larger than F1.4, regardless of the refractive index n of the glass material. That is, in a color separation optical system constituted by three prism systems, the limit is around F1.4. Further, when the refractive index n of the glass material of the prism is n = 1.7, the intersection of the condition (1) of A and the condition (2) of B is larger than the case where the refractive index is n = 1.5. Fno is F1.4
It is a slightly larger point.

In the graph of FIG. 6, C denotes the diameter of the objective lens Le, which is 2/3 ", and the first value is F1.4, which is almost the limit of F1.4.
Calculate the minimum optical path length (Lmin) required for the prism,
7 is a graph showing the amount of change from a reference value of 0 for an optical path length at a refractive index of 1.55.

As a condition, Θ1 is an intermediate value between the upper limit value of Expression (1) and the lower limit value of Expression (2) (4) If Fno is 1.4 (5), 1 = [3 × Sin ^{− 1} (1 / n) -Sin ^-1 {1 / (2n · Fno)}] / 4, and the imaging size d1 in the scanning direction on the exit surface of the first prism is 6.6 mm (6) Prism The distance from the exit plane to the imaging plane is 5mm ...
From (7), the shape, size, material, and the like of the objective lens Le and the first to third prisms are determined.

As shown in FIG. 8, the effective luminous flux length at a position (plane) distant from the imaging plane is represented by the distance (air conversion length) from the imaging (imaging) plane and Sin ^-1 ｛1 / (2 · Fno). ) Expressed by the following equation at the angle of｝, (effective beam length) = d1 + 2 × (distance from the imaging surface) × tan [Sin ^-1 ｛1 / (2 · Fno)｝]… (8) Becomes

Using these conditions, Lmin = (effective luminous flux length at the exit surface) × sin (2 × Θ1) ｛2 × cos (2 × Θ1) +1｝ (9) L when the refractive index n = 1.55 is
18.347.

It can be seen from the graph that the color separation prism itself can be made smaller as the refractive index becomes higher.

The definition of a high-resolution HD system by the Broadcasting Technology Development Council (BTA) of an arbitrary organization that creates standards in the broadcasting field (Broadcasting Technology Development Council Technical Document BTAS
In -1005-A), the refractive index is set to 1.612 as a recommended glass type, so that the optical path length of the prism in consideration of ghost and the like is approximately 34.0 mm.

[0017]

A television camera for broadcasting (hereinafter abbreviated as a television camera) employs an interchangeable lens. In order to maintain the interchangeability of the lenses, it has been agreed that the air-equivalent length (hereinafter referred to as FB) from the lens mounting surface (F) for mounting the lens to the television camera to the image forming surface is constant. This is a rule that the best focus can always be obtained on the image sensor even if the type of glass (refractive index) between the surface F and the imaging surface changes.

Further, since the thickness of the glass between the lens and the imaging surface affects the spherical aberration, the thickness of the glass between the surface F and the imaging surface is also determined.

However, the actual (physical) distance (hereinafter, referred to as FBr) between the surface F and the image forming surface changes as the refractive index of the prism changes.

The graph of FIG. 7 is obtained by adding the graph D of the change amount of the FBr length due to the change in the refractive index of the prism to the graph C of FIG.
The amount of change was defined as 0 when the refractive index was 1.55, and expressed as the amount of elongation therefrom.

As can be seen from FIG. 7, increasing the refractive index of the prism shortens the optical path length of the prism but increases the FBr length.

Recent television cameras are required to be capable of capturing high-resolution images in response to public demand for high images. However, since the operating frequency of a high-resolution imaging device is increased, the amount of heat release is extremely large, ie, two to three times that of the current case. Furthermore, especially television cameras for broadcasting are still large, and it is difficult to increase the size even if the resolution becomes high. However, if the size of the camera housing is the same as the current one and the prism alone is reduced in size by increasing the refractive index of the prism, the FBr grows and cannot fit in the camera housing. There is an inevitable problem.

Further, in a handheld television camera, which has a strong demand for miniaturization, a sufficient amount of light is not always given at the time of shooting, so that a light beam that can pass through the prism must pass a brighter light beam. , Fno cannot be increased.

[0024]

As described above, the interchangeability of the interchangeable lens is maintained, and the interchangeable lens is built in a high-resolution television camera device having more than 625 scanning lines, and is disposed between the objective lens and the solid-state image pickup device. In the color separation prism, three prisms of a first prism, a second prism, a third prism, and a first prism and a second prism are configured to pass through an air layer from the objective lens side. In the case of a prism having the ability to pass the light flux of the lens of the above (3), the refractive indices of the three prisms are to be smaller than 1.6.

Further, the present invention provides a high-resolution television camera device having more than 625 scanning lines while maintaining the interchangeability of the interchangeable lens, and is disposed between the objective lens and the solid-state image pickup device. From three prisms of a first prism, a second prism, and a third prism.
The first and second prisms are provided with an entrance surface, an exit surface, and a transmission surface, respectively, and are disposed via an air layer, and have a capability of transmitting a light beam of a lens of approximately F1.4. And the refractive indices ne of the three prisms
Is characterized in that a color separation optical system characterized by being smaller than 1.6 is built in.

By using the optical system, the television camera can be stably used for a long time while preventing the size of the entire television camera system from being reduced, although the miniaturization of the prism itself is alienated.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described.
This will be described in detail with reference to the drawings.

[First Embodiment] FIG. 1 shows a first embodiment of the present invention.
It is principal part sectional drawing of the color separation optical system by embodiment.

In FIG. 1, Le is an objective lens, MT is a mount for connecting the objective lens to the camera, F is a flange surface connecting the objective lens and the camera, Ca is a camera housing, and 101 is a color separation prism. is there.

The color separation prism is a first prism from the objective lens side.
, A second prism, and a third prism. An air gap 105 is provided between the first prism and the second prism, and the second prism and the third prism are bonded by bonding. ing.

The objective lens Le collects a light beam from an object (not shown) and guides the light beam to a color separation prism. In addition, P is a printed circuit board.

The first prism of the prism 101 has an entrance surface 102 substantially facing the lens surface of the objective lens Le,
The light from the lens incident from the incident surface 102 is transmitted to the transmission surface 1.
Only the blue light is reflected by the blue reflection dichroic film applied to No. 03, and the rest is transmitted. The reflected blue light is totally reflected on the incident surface 102, exits the emission surface 104, and travels toward the solid-state imaging device 111B.

The light transmitted through the transmission surface 103 passes through the air gap 1
The light is incident on the incident surface 106 of the second prism through 05. The red reflecting dichroic film applied to the transmission surface 107 of the second prism reflects only red light and transmits remaining green light. The reflected red light is totally reflected on the entrance surface 106 of the second prism in contact with the air gap 105, and the exit surface 1
08 to the solid-state imaging device 111R.

The green light transmitted through the transmission surface 107 enters the entrance surface 109 of the third prism, exits the exit surface 110, and travels toward the solid-state image pickup device 111G. In this way,
The color separation prism separates the light beam. The entrance surface 109 of the third prism is disposed in contact with the transmission surface 107 of the second prism, and the inclined surface thereof is in contact with the transmission surface 107 of the second prism.

The transmission surface 103 of the first prism and the second
It faces substantially parallel to the entrance surface 106 of the prism via the air gap 105. Then, the transmission surface 103 of the first prism is formed at an angle at which only the blue wavelength component is reflected, totally reflected by the incident surface 102, and the blue component is emitted from the emission surface 104. Angle to angle θ
1. Also, the second prism is shaped so that the angle between the incident surface 106 and the transmitting surface 107 is an angle θ2.

FIG. 2 shows that the refractive index n at F1.4 is 1.
It is a graph of the relationship between 54 to 1.64 and (θ1max−θ1min). (Θ1max-θ1mi
In the range of the refractive index where the value of n) is negative, it indicates that the apex angle θ1 of the prism in FIG. 1 does not have a real range for realizing F1.4. Therefore, in the case of a color separation prism having an air gap between the first prism and the second prism, a large aperture of F1.4 can be realized by making the refractive index smaller than n = 1.6.

FIG. 3 shows a prism designed in consideration of a ghost and the like, with the refractive index of the prism at e-line being 1.574 (Embodiment 1) and 1.551 (Embodiment 2). The main numerical values of a prism having a ratio of 1.612 are shown in a table.

In FIG. 3, the optical path length of each of the prisms of Examples 1 and 2 was 34.5 mm. Compared with the optical path length 34.0 of the prism having a refractive index of 1.612 shown in the conventional example, the length of the prism is increased by about 0.5. However, FBr has a refractive index of 1.612.
Based on the conventional example, the amount of change is about-
FBr can be reduced to 0.5 and about -0.8.

Even if the optical path length of the prism having a refractive index of 1.612 shown in the conventional example is designed to be about 10% smaller than 34.0, and the optical path length of the conventional prism is designed to be about 10% larger than 34.5, the refraction will not occur. Since the optical path length of the prism having the ratio of 1.612 is replaced with the refractive index of the embodiment (1.574 in the first embodiment and 1.551 in the second embodiment), there is no change in that the FBr can be reduced.

The dispersion of e-ray is shown in the table of FIG. 3. In both the first and second embodiments, the chromatic aberration of the lens is set near the dispersion (46.5) of the conventional example shown in the embodiment. Can be kept unchanged from the conventional example.

Then, preferably, the refractive index n of the prism
It is desirable to use a glass material with e being 1.55 <ne <1.575 and a dispersion νe of 42.5 <νe <50.5. Further, as in the above-described embodiment, both apex angles of the first prism and the second prism are set to θ1 = 26.5 degrees,
It is preferable to set θ2 = 39.75 degrees.

The apex angle (θ1) of the first prism and the apex angle (θ2) of the second prism are shown at the end of the table of FIG. These are different between the embodiment and the conventional example in consideration of the conditional expressions (1), (2) and (3).

As described above, in the present embodiment, it is preferable that the refractive index n be smaller than 1.60. However, if the refractive index n is too small, the size of the color separation prism lens becomes large. It is only necessary to judge that there is a limit based on technical common sense.

[0044]

As described above, by using the prism of the present invention, the distance from the flange surface to the imaging surface can be kept small while realizing a large aperture of F1.4. Thereby, even if the high-resolution image sensor emits a large amount of heat, it is possible to keep a sufficient distance from the electric board, and as a result, it is possible to prevent the TV camera system from being enlarged. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a main part of a high-resolution imaging camera according to the present invention.

FIG. 2 is a diagram showing the relationship between the refractive index and the existence range of the prism apex angle according to the present invention.

FIG. 3 is a characteristic table in which a refractive index of an example of the present invention is used as an index.

FIG. 4 is a schematic diagram of a main part for explaining a conventional technique.

FIG. 5 is a diagram showing a relationship between Fno and a prism apex angle in a conventional example.

FIG. 6 is a relationship diagram between Fno and a prism optical path length in a conventional example.

FIG. 7 is a diagram showing a relationship between Fno and a real distance between a flange surface and an image forming surface in a conventional example.

FIG. 8 is a diagram illustrating conditions of a conventional example.

[Explanation of symbols]

 101, 1001 prism 102, 1002 entrance plane 103, 1003 transmission plane 104, 1004 exit plane 105, 1005 air gap 106, 1006 entrance plane 107, 1007 transmission plane 108, 1008 exit plane 109, 1009 entrance plane 110, 1010 exit plane 111B , R, G imaging unit Le imaging lens MT mount F contact

Claims (10)

[Claims] 1. A high-definition television camera device having more than 625 scanning lines, is disposed between an objective lens and a solid-state imaging device, and includes a first prism, a second prism, The third prism is composed of three prisms in this order and separates the three colors. The first and second prisms each have three surfaces of an entrance surface, an exit surface, and a transmission surface, and are arranged via an air layer. A color separating optical system having a capability of transmitting the light beam of the objective lens of F1.4, wherein the refractive indices ne of the three prisms are each smaller than 1.6. 2. The color separation optical system according to claim 1, wherein the dispersion νe of the color separation prism satisfies 42.5 ≦ νe ≦ 50.5. 3. The color separation optical system according to claim 2, wherein the refractive index ne of the color separation prism satisfies 1.55 <ne <1.575. 4. The color separation optical system according to claim 3, wherein a vertex angle (θ1) between the incident surface and the transmission surface of the first prism of the color separation prism is 26.5 degrees. 5. The color separation optical system according to claim 4, wherein a vertex angle (θ2) between the incident surface and the transmission surface of the second prism of the color separation prism is 39.75 degrees. 6. A high-resolution television camera device having more than 625 scanning lines, while maintaining the interchangeability of the interchangeable lens, disposed between the objective lens and the solid-state image sensor, and the first lens from the objective lens side. The first and second prisms are each composed of three prisms of a prism, a second prism, and a third prism, and each of the first and second prisms has an entrance surface, an exit surface, and a transmission surface. And is arranged approximately through F
A prism having the ability to transmit the light beam of the lens of 1.4, wherein the refractive indices ne of the three prisms are each 1.
A television camera incorporating a color separation optical system, wherein the color separation optical system is smaller than 6. 7. The television camera according to claim 6, wherein the dispersion νe of the color separation prism satisfies 42.5 ≦ νe ≦ 50.5. 8. The television camera having a built-in color separation optical system according to claim 7, wherein the refractive index ne of the color separation prism satisfies 1.55 <ne <1.575. 9. The color separation optical system according to claim 8, wherein a vertex angle (θ1) between the incident surface and the transmission surface of the first prism of the color separation prism is 26.5 degrees. Built-in TV camera. 10. A vertex angle (θ2) between the entrance surface and the transmission surface of the second prism of the color separation prism is 39.
10. A television camera having a built-in color separation optical system according to claim 9, wherein the angle is 75 degrees.