JPS633282B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical path changing device used in combination with, for example, a transmission screen.

As shown in FIG. 1, a conventional rear projection television apparatus focuses image light generated by a color cathode ray tube 1 onto a transmission screen 3 from the back of the tube through a projection lens 2, and projects the image from the front of the screen 3. I try to look at the statue. The transmission screen 3 has a scattering surface. Transparent screen 3
The principal axis of the transmitted light coincides with the path of the projected light when there is no scattering surface, so the light at the periphery of the projected image is
Most of the images are directed outwards, and a front-facing viewer can only see a bright image in the center.

In order to improve this problem, a Fresnel convex lens 4 is disposed between the projection lens 2 and the transmission screen 3 and near the screen 3, as shown in FIG. I try to bend it. However, even if the Fresnel convex lens 4 is used, the directivity cannot be improved sufficiently, and since refraction is used, if the optical axis is bent by the necessary amount, color splitting will occur due to the prism effect. The problem was that the image quality deteriorated.

The present invention takes the above-mentioned points into consideration and provides an optical path changing device that can bend the optical path of image light, etc. directed toward the periphery inward.

An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 3, notches 6 are pressed concentrically at a predetermined pitch, e.g., 1 mm, in a transparent plate 5 made of, for example, acrylic resin, which has approximately the same size as the transmission screen and has a relatively high refractive index. Formed by process. The transparent plate body 5 is 100
It has a size that corresponds to a 50-inch screen measuring [cm] x 75 [cm] and a thickness of 3 [mm]. Notch 6
is not formed near the center of the transparent plate 5, but is formed so that the depth increases toward the periphery, as shown in an enlarged view in FIG. mm]. That is, FIG. 4 shows an enlarged cross section of the transparent plate 5 at the upper and lower outer peripheral portions having widths D ₁ and D ₂ and at the center side having a width D ₃ . The cutout 6 has a substantially wedge-shaped cross section, and a wall surface 6a on the center side thereof is aligned with the thickness direction of the transparent plate 5.

The optical path changing device according to this example is used by being provided close to the back surface of the transmission screen 3, as shown in FIGS. 4 and 6. In this case, it goes without saying that the transmission screen 3 may be brought into close contact with the transparent plate 5, or that a scattering portion may be provided integrally with the transparent plate 5 on its surface to function as a screen. As shown in FIG. 5A, ambient light directed outward from the center of a video light emitting source, for example, a color cathode ray tube, enters the transparent plate 5 and passes through the wall surface 6 of the notch 6.
is incident on a. Since this incident angle θ ₁ is greater than the critical angle, total reflection occurs on the wall surface 6a, and even at the reflection angle θ ₁ the light is taken out in front of the transparent plate 5. This figure 5A
indicates an optical path at the outer peripheral portion of the transparent plate 5. On the other hand, closer to the center of the transparent plate 5, as shown in FIG. 5B, the degree of diffusion of the image light from the color cathode ray tube 1 is reduced, so the depth of the wedge-shaped notch 6 is made shallower. There is. Along with this, the amount of reflected light is corrected depending on the depth of the notch 6,
The reflected light is made to increase closer to the periphery of the transparent plate 5.

As shown in FIG. 6, the optical path changing device according to this embodiment bends the image light generated in the color cathode ray tube 1 and passed through the projection lens 2 inward and applies it to the transmission screen 3. It is possible to prevent brightness from decreasing around the image. Furthermore, since the surrounding light is bent inward by reflection, there is no risk of color breakup due to prism effect.

In addition to utilizing total reflection, the wall surface 6a of the notch 6 may be configured to serve as a reflective surface, such as by filling the inside of the notch 6 with a reflective material. Of course, the method of forming notches in a transparent synthetic resin plate by a pressing process, as in the above-mentioned embodiment, has the advantage that a simple and low-cost optical path conversion device can be realized. Furthermore, the notch 6 is not limited to a concentric shape, but may be shaped into a combination of straight lines such as a rectangle, or the notch 6 may have a shape that is a combination of straight lines such as a rectangle.
Various modifications are possible, such as obtaining a desired directivity by changing the angle of a, and providing an opaque portion or a light absorption layer to absorb external reflections and internal unnecessary scattered light.

[Brief explanation of the drawing]

1 and 2 are configuration diagrams used to explain a conventional projection television apparatus, FIG. 3 is a plan view of an embodiment of the present invention, FIG. 4 is a partially enlarged sectional view thereof, and FIG. 5 6 is a schematic diagram used for the explanation, and FIG. 6 is a configuration diagram when the present invention is applied to a projection television apparatus. 1 is a color cathode ray tube, 2 is a projection lens, 3 is a transmission screen, 5 is a transparent plate, 6 is a notch, 6a
is the wall on the center side.

Claims (1)

[Scope of Claims] 1. A large number of concentric strip notches are formed at regular intervals on one surface of the transparent plate, and the strip notches extend from the one surface of the transparent plate toward the other surface. The depth of the strip notch becomes deeper toward the periphery of the concentric circle, and the light rays projected from the other surface of the transparent plate are shaped like a wedge. The optical path conversion device is configured to be substantially totally reflected on the side surface of the strip cutout and transmitted to the one surface side, so that the projected light beam has a substantially equal amount of light at the periphery and center of the transparent plate body.