JPS6042701A - color television camera - Google Patents

Abstract

PURPOSE:To enable increase in the aperture diameter of the four color sepn. prisms of a color sepn. prism system and to reduce the size of a color TV camera by setting the refractive indices and vertical angles of the color sepn. prisms at prescribed values. CONSTITUTION:A color sepn. prism system have the 1st, 2nd, 3rd and 4th prisms from an objective lens 4 side along the optical axis of an objective lens 4. The 1st prism 10 and the 2nd prism 11 as well as the 2nd prism 11 and the 3rd prism 12 face respectively each other via air layers. The 1st die chroic layer 11'' is formed on the face of the 2nd prism 11 facing the 3rd prism 12. The 3rd prism 12 and the 4th prism 13 are joined via the 2nd dichroic layer 12''. The prism system is so manufactured as to satisfy the equation I - the equation III when the vertical angles of the prisms 10, 11, 12, 13 are designated as theta10, theta10+theta11, theta12, theta13 and the refractive indices of the materials constituting the respective prisms are designated as (n).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to color television (TV) cameras, and more particularly to color television (TV) cameras, and more particularly to color television (TV) cameras.
, relates to a color separation prism system that separates the luminous flux from an object into colors.

In a color TV camera, a color separation prism system is placed behind the objective lens to separate the incident light beam into three color wavelength regions.
An image is formed on six imaging elements corresponding to each wavelength region. Each image sensor scans the image plane and converts the image into an electrical signal.

Konera's color TV cameras, especially color handy TV cameras for news gathering, are required to be as light and compact as possible, so we have made the image size small.
Efforts are being made to downsize color separation prism systems and imaging devices.

For example, in an image pickup tube, the light receiving surface converts the energy of the light that reaches it into an electric current by scanning an electron beam to obtain an output signal. Therefore, when the image size is reduced and a 4-F number objective lens is used to photograph the same subject, the light energy per unit area on the light receiving surface is the same.

Since the beam cross-sectional area becomes smaller in proportion to the image size, the output voltage bI1. decreases. This is because reducing the image size makes it less sensitive. Therefore, in order to avoid a decrease in the sense of 1W,

However, the conventional color separation prism shown in Figure 1, which is composed of three prisms, has an F number of 1.4.
However, it was difficult to increase the diameter.Here, we will first summarize the problems using the conventional example shown in Figure 1. The imaging light beam emitted by the objective lens 4 enters the prism 1 from the incident surface 1' of the color separation prism system, and only the light in the blue region, for example, is reflected at the surface 1' coated with a dichroic film. 1', unnecessary wavelength components are cut by the trimming filter 6B, and then the light-receiving surface of the image sensor 5B? The image is focused on B'.

The light flux transmitted through the dichroic surface 1' enters the second prism system 2, and only the light in the red region, for example, is reflected by the dichroic film 21 provided between the first prism system 1 and the 21st rhythm system 2. Further, the light is totally reflected at the boundary surface 2' with the parallel air gap, and unnecessary wavelength components are cut off by the n trimming filter 6R, and then an image is formed on the light receiving surface 5'H of the image sensor 5R. The light flux, for example, light in the green region, transmitted through the dichroic surface 2 passes through the prism 3, unnecessary wavelength components are cut off by the trimming filter 6G, and then an image is formed on the light-receiving surface 5F() of the image sensor 5G. Further, the shape of the prism system is determined by specifications such as the refractive index n and FNO of the glass material used. As shown in Figure 1, the first IJ rhythm 1
, the angle between the light incident surface of the prism 2 and the dichroic surface is θ1. Assuming that θ is the angle between the light entrance surface 2 and the light exit surface 3' of the third prism system 3, these angles must satisfy the following conditional expression.

θ, <5tn-1 (1/n)-8in-' (1/2n
FNO) −, , (3)2θ,')Sirr' (
1/n)+81n-' (1/2n FNO) ---
, (4) 2θ, nθ, -1-8iy' (1/n)-
)SiFl(1/2nFNo) ,, (s)θ,=
θ, -θ, ...(6) However, conditional expression (3) requires that the wavelength range light that should be transmitted through dichroic surface 1' is not totally reflected at surface 1', and conditional expression (
4) means that the wavelength range light reflected on dichroic surface 1' is totally reflected on surface 1', and conditional expression (5) means that the wavelength range light reflected on dichroic surface 2 is totally reflected on surface 2'. Since conditional expression (6) requires that the entrance surface 1' and the exit surface 5' be parallel, each of K is required.

If we pay attention to the angle between the light incident surface of the first prism system 1 and the dichroic surface, that is, the angle θ1 between the optical axis and the dichroic surface 1', the range in which the angle θ1 can exist is based on the condition (
3) It is determined from the refractive index n of the glass material and the F number according to (4).

FIG. 2 shows this matter, and shows the relationship between the F number and the angle θ using the refractive index n of the glass material as a parameter.

From this graph, it can be seen that the range of the angle θ1 that satisfies the equation <3) (4) t-simultaneously is limited to a range where the F number is greater than 1.4, regardless of the refractive index n of the glass material. In other words, in a color separation prism system composed of six prisms, the maximum F number is 1.4, and even if a brighter lens is used, normal reflection and total reflection will not occur, so it will not be possible to achieve the desired color separation. Symptoms are not executed.

As mentioned above, with conventional color separation prisms, only an objective lens with an F number of 1.4 mm can be used, so if you reduce the image size and downsize the camera, it will be difficult to use.
It had the disadvantage that it was inevitably subject to a decrease in

On the other hand, there is a measure to alleviate the brightness limit of the color separation prism system composed of three prisms [N8W Came].
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That is, as shown in Fig. 3, the first color separation prism system in the conventional color separation prism system
In order to incline the entrance surface of the prism by an angle θ1o in the dichroic surface and the direction of reflection, and to make the entrance surface and exit surface 3' of the color separation prism system parallel, the apex angle of Kakuryu θ1o is set in the first row of prisms 1. A wedge-shaped prism with a parallel air gap is provided. In this case, the above-mentioned conditional expression (4) is transformed as follows.

2θ1. 10-0≧sin'(1/n)+sin'
(1/2n FNO), °, 2θ, 1≧sin→(1/
n)-1-sirr' (1/2n FIIO)-
〇、. (4)' This means that the curve (4) in Figure 2 is θ+
This corresponds to moving down by e/2 and moving the intersection with (3) to the left, to the side with the smaller JF number. In this new color separation optical system composed of four prisms, it is possible in principle to use a color separation prism that can use an objective lens with an F number brighter than 1.4, for example, an F number of 1.2.

However, as a result of the study conducted by the inventor of the present invention, it was found that with this color separation prism system arrangement, the glass optical path length increases due to an increase in the number of constituent prisms, and as the F number decreases, the incident surface becomes larger or the number of surfaces increases. It has been found that there are problems such as the occurrence of ghosts due to this.

The present invention aims to solve the above problems, and in particular,
The purpose is to prevent the size from increasing despite the small number. Therefore, in a television camera that forms and captures monochromatic images on the imaging surfaces of a plurality of imaging devices 5R, 5G, and 5B using the objective lens 4 and the color separation prism system, the color separation prism system shown in FIG. is the first one counted from the objective lens side along the optical axis of the objective lens. Second. Fifth. It has a fourth prism, @1 prism 10 and a second prism 11, and a second prism and a third prism.
The prisms 12 face each other with an air gap in between, and a dichroic layer of FifMl is formed on the surface of the second prism facing the third prism, and the third prism and fourth prism 15 are joined via the second dichroic layer. When the apex angle of the first prism is θIOy and the refractive index of the prism constituent material is n, the following conditions are satisfied.

n) 1.6 5.13≦θ,. (15° A detailed explanation will be given below using FIG. 6.

θK related to the apex angle of each prism. , θI+θI! +01
The conditions 3 must be satisfied are as follows.

θ11≦5irr'(-)-e'in-'(-Foo)
-----・(3)n 2n is 1/2 of the short side dimension of the screen, and L is the distance in air between the exit pupil of the objective lens and the image plane.

, 2θ1. ') Sirrl (-!-) 4- Bir
r' (-Fno,) ・, ,, -(sl-n 2n θIB=01.-〇,, ,,,,,, (6) Here, conditional expression (4)' is reflected by the dichroic surface 11'. It is provided so that the effective imaging light beam is totally reflected on the surface 11'.
θ, 1. θ17. θ1. This is the same as the conventional system consisting of three prisms. Also, α included in equations (4)' and (4) is a note to prevent ghosts from occurring in the image formed on the light-receiving surface 5B'. This will be explained using clear and developed diagrams, Figures 4 and 5.

The light beam that forms an image on the light-receiving surface 5'B' is normally the light shown in Fig. 4,
%lA, B, the light beam is reflected by the dichroic surface 11' and further totally reflected by the interface 11' with the air gap.

However, with a normal objective lens, the distance Gf between the exit pupil 4P and the image plane
For example, in FIG. 4, the light receiving surface B'
The imaging light flux heading toward the upper end of the lens passes through paths O and D and is tilted with respect to the on-axis imaging light fluxes A and B. Moreover, this inclination is in a direction in which the angle of incidence becomes smaller for +fii I which is totally reflected. In order to design the glass optical path length of the color separation prism system to be short, each apex angle is set to (3) with respect to the axial luminous flux B.
(4) ' (5) Since it is often determined to be as small as possible within the range that satisfies (6), the surface 1' of ray A
The angle of incidence is often approximately equal to the critical angle. In such a case, among the rays heading towards the upper end of 5B', C
The angle of incidence on the surface 1' becomes smaller than the critical angle, and a portion of the ray is transmitted. As shown in FIG. 5, this transmitted light is further partially reflected by the entrance surface 10' of the prism 10, forming a ghost. This ghost is likely to appear when the objective lens is used close to its maximum aperture and the subject includes bright areas, and since it is almost in focus, it significantly impairs the image. In order to avoid this ghost, set θ so that all the light flux is totally reflected at 1'. If you increase this increment α
It is. The angle between A and C is maximum tsn-' (S/L
×n), α is determined within the range of (4Y).

The conditions set based on the situation are 5.1°〈θ+
o<15° −, −(7). In order to shorten the single prism surface and make it a feasible dimension, we set n≧1.6 (8).

Furthermore, in order to facilitate the design, it is desirable to consider the following conditions.

16.69 θ, 1≦24.1°−, (9) 32.6
°≦θ,,<j8.7°,:',,(1o)θIs=
θ1. -θ, I where θ wealth 1. θ71. θ1. 2nd in order. Third. Fourth
This is the apex angle of the prism.

If the upper limits of conditions (9) and (10) are exceeded, the prism becomes larger and the generation of ghosts becomes uncontrollable, and if the lower limits are exceeded, it becomes extremely difficult to realize a prism system with a small y-number, which is the objective of the present application. becomes.

Next, reduce the F number and increase the optical path length to 35 mm.
Below are examples of numerical values that could be achieved through miniaturization.

Numerical example 1 1 III Refractive index 1.6 1.65 1.7 F number 1.2 1.2 1.2 Screen size 4.8 X 6.4 4.8X6.4 4
．． 8X (including S, 4) (same as left) θ,. 5.1° 5.5° 7°θu 24,1° 25° 22°θ,! 38.7° 67.5° 56' Convergence value example y ”
i Vi Refractive index 1.75 1,65 1.75F number 1
,2 1.2 1.2 Screen size 66X8. e 4.8x: 6.4 6.6
ni8J3θ1° 5.5' 15° 15°θ++ 21.5° 18.5° 16.6°θ1t3
5° 55.5' 52.6° As described above, according to the present invention, the color separation prism can be made larger in diameter, and therefore it can be made smaller, which in turn has the effect of making the color TV camera smaller. It is something.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional color separation prism system. What about figure 2? A diagram showing the relationship between the number, the apex angle of the P41 prism, and the refractive index. FIG. 3 is a sectional view showing an embodiment of the present invention. Figures 4 and 5 are optical development views. In the figure, 4 is an objective lens, 5R, 5G, 5B is a camera tube, 1
0 is the first prism, 11 cylinders 2 prisms, 12 is the 5th prism, and 13 cylinders 4th prism.

Claims (1)

Scope of Claims: (1) In a television camera that forms and images monochromatic images on a plurality of imaging planes a using an objective lens and a color separation prism system, the color separation prism system includes the objective lens and a color separation prism system. The first one counted from the objective lens side along the optical axis of
, 2nd degree, 3rd degree. It has a fourth prism, the first prism and the second prism, and the second prism and the third prism face each other via an air layer, and the surface of the second prism facing the sixth prism has a first prism. dichroic layer is formed, and the third dichroic layer is formed.
The prism and the fourth prism are connected via a vJ2 dichroic layer, and the first, second, third, and fourth prisms are
The apex angle of the prism is 010,01G+611°θ11
．． When θ11 and the refractive index of the constituent material of each prism are n, n≧1.6 5.1°〈θ,. <15°θ, 3=01! −〇、. A color television camera that satisfies the following conditions. (2) Each apex angle of M2, A3, and the fourth prism is θ5. θ17. θ1. When ? 16.6°<θ, , <14.1° 32.6°<θ, , <18.7°. The color television camera according to claim (1).