JPS6326365B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a projection type image display device for enlarging and projecting a television image or the like on a projection screen.

There are various projection television systems for enlarging and projecting a television image on a projection screen, each of which has advantages and disadvantages. The concave mirror reflection type, which has the highest luminous flux utilization rate, is usually constructed as shown in FIG. The image is projected as an enlarged image onto a projection screen (not shown) through a correction lens 4. In this case, CRT 1
The utilization rate of the luminous flux emitted from the luminous screen 2 can be improved by increasing the half angle θ ₁ of the concave mirror 3 toward the peripheral portion 7, and the brightness on the projection screen can be improved. However, the aberration of the concave mirror 3 increases rapidly as it moves away from the optical axis 5. The limit of aberration correction is when the half angle θ 1 from the central part 6 of the luminescent screen of the cathode ray tube ₁ to the peripheral part 7 of the concave mirror 3 is around 50 degrees, and it is extremely difficult to achieve a luminous flux utilization rate of 50% or more. .

Therefore, the present inventor has proposed a projection type image display device that can efficiently focus the luminous flux emitted from the luminescent screen 2 of the cathode ray tube 1 within the plane of the concave mirror 3, and obtain a high luminous flux utilization rate (Japanese Patent Publication No. 1983-1999-1).
Publication No. 59786). As shown in Figure 2, this
The space of the optical system in the figure is filled with an optical medium 8 with a refractive index greater than _1. According to theoretical calculations and experiments, the critical angle sin _-1 ⁽ 1/μ ₁ ), the luminous flux utilization factor is approximately μ ₁ ² of the luminous flux utilization factor shown in Figure 1.
It can be expected that the brightness will be doubled and the brightness will be significantly improved. In addition,
9 indicates a concave mirror.

An object of the present invention is to significantly improve aberrations at the periphery of a projection screen in an optical system of the type shown in FIG. Note that in the conventional structure shown in FIG. 1, it is extremely difficult to significantly improve aberrations in the peripheral area of the projection screen.
This is because the aberration correction lens 4 is almost uniquely determined by the projection magnification, projection distance, radius of curvature of the concave mirror, and refractive index of the aberration correction lens material. Even if it is possible to completely correct aberrations, it is hardly possible to correct aberrations for the light beams emitted from the periphery of the luminescent screen.

The present invention has been made with the above-mentioned problems in mind, and is a projection type image display device that can not only increase the luminous flux utilization rate of the projection optical system but also further improve the aberrations in the peripheral area of the projection screen. It provides:

Next, the present invention will be described with reference to embodiments thereof.
3 to 5 each show an embodiment of the present invention, and show a front glass 10 of a cathode ray tube 1.
The light emitted from the phosphor film 11 coated on the inner surface of the phosphor passes through the first optical medium 8 having a refractive index of μ ₁ , which is larger than 1, and is reflected by the concave mirror 9 made of a vapor-deposited aluminum film. The light enters the optical medium 8 again and is emitted into the air through the aberration correction lens section 12, which is a second optical medium having a refractive index of μ ₂ larger than 1, and reaches a projection screen (not shown). Fourth
In the embodiment shown in FIG. 5 and FIG. 5, the length of the aberration correction lens section 12 in the optical axis direction is very long. Further, in the embodiment shown in FIG. 4, the aberration correction lens section 12 is formed of two parts, but it may be formed of three or more parts depending on the convenience of processing and assembly. In addition, the aberration correction lens section 1 can be constructed by combining two or more types of components with different refractive indexes.
2 may be formed.

FIG. 6 is a diagram for explaining the principle of the present invention, and shows three typical light rays directed from the optical system 13 toward the periphery of the projection screen 14. Optical medium 1
When 5 and 16 are made of the same material, no refraction of light occurs at the interface 17 between optical media 15 and 16, resulting in light rays shown by solid lines a, b, and c. In this case, the light ray a tends to be overconvergent with respect to the light ray b, and the light ray c tends to be underconvergent. Therefore, the optical medium 16
When the refractive index μ ₂ of the optical medium 15 is made larger than the refractive index μ ₁ of the optical medium 15, a light refraction effect occurs at the interface 17, and the light rays a, b, and c become a′ and b′c′, respectively, shown by broken lines. (Of course, the curved surface of the correction lens must be recalculated depending on the material of the optical medium.) rays of light
a′ tends to be less convergent than ray a, and ray c′ tends to be less convergent than ray a.
However, the ray b does not change much with respect to the ray b'. Therefore, projection screen 1
Aberrations at the periphery of the lens 4 are significantly improved by the refractive effect at the interface 17. The improvement effect is greater when μ ₂ is larger than μ ₁ . In this way, the optical medium between the reflecting mirror 18 and the light beam exit surface 19 is configured with at least two types of refractive index,
By appropriately selecting this refractive index, it is possible to obtain an image projection system with extremely few aberrations. Further, it is desirable that the thickness of the optical medium 16 be as thick as possible within a range that does not exceed the cathode ray tube screen 11.

In the configuration described so far, it has been assumed that the center position of the aberration correction lens surface coincides with the center of curvature of the reflecting mirror 18, as shown in FIG. 7a.

On the other hand, as is clear from FIG. 6, aberrations particularly contribute to the light ray c that passes near the outermost periphery of the lens compared to other light rays. This is because the inclination of the correction lens surface changes rapidly from near the outermost periphery of the lens, which greatly affects the light rays passing through it. Therefore, for example, the effective diameter of the correction lens should be reduced equivalently to the light ray c, and the light ray c should be prevented from passing around the lens as much as possible. The lens surface may be positioned on the reflecting mirror 18 side within a range that does not disrupt the balance of the optical system, and this situation is shown in FIG. 7b.

As has become clear from the above description, according to the projection image display device of the present invention, the image light emitted from the cathode ray tube passes through the first optical medium having a refractive index greater than 1 and reaches the reflecting mirror. The reflected light passes through the first optical medium again and then passes through the second optical medium and is emitted, which not only increases the light focusing efficiency but also improves the efficiency of the second optical medium. Since the refractive index of the first optical medium is larger than the refractive index of the first optical medium, spherical aberration, especially aberration in the peripheral area, can be significantly improved, and a high-resolution projected image can be obtained with high brightness. .

[Brief explanation of the drawing]

1 and 2 are block diagrams of main parts of a conventional projection image display device, FIG. 3 is a block diagram of main parts of an embodiment of the present invention, and FIGS. 4, 5, and 7a, 6b is a block diagram of a main part of another embodiment of the present invention, and FIG. 6 is a diagram illustrating the principle of the present invention. 1... Braun tube, 2... Luminous screen, 8
... Optical medium, 9 ... Concave mirror, 10 ... Optical medium, 1
2...Aberration correction lens section.

Claims (1)

[Claims] 1. A first optical medium provided between a front glass of a cathode ray tube and a concave mirror has a surface in contact with the front glass, a convex surface in contact with the concave mirror, and a second optical medium that transmits reflected light transmitted through the optical medium. the first and second optical media have a surface in contact with the optical medium, the first and second optical media are larger than 1, and the second optical medium has a refractive index of the first
A projection type image display device characterized in that the refractive index of the optical medium is greater than that of an optical medium.