JPS62249572A - Projection type television receiver - Google Patents

Abstract

PURPOSE:To obtain a projected image with excellent picture quality even if a video tube is arranged with a prescribed inclination from the optical axis of a projection lens by filling the space between the video tube and its adjacent lens element with a transparent substance and forming one side of the lens element as a convex surface. CONSTITUTION:The space between the lens element 21 and the face plate 24 of the video tube 20 is filled with the transparent substance 22. The difference of refractive indexes between the transparent substance 22 and the lens element 21 is selected as a value <=0.3. The lens surface 28 of the video tube side of the lens element 21 is formed like a spherical convex surface and the surface 29 of the opposite side is formed like a concave surface so that the curve on the image surface can be corrected. Even if the video tube 20 is inclined with a prescribed angle from the optical axis of the projection lens 18, the interval between the lens element 22 and the video tube 20 measured on the optical axis 23 can be shortened. Thus, the projection image of excellent picture quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a projection television device that enlarges and projects an image projected on an image display device onto a screen using a projection lens. The present invention relates to a projection television device that projects onto a screen from an oblique direction.

2. Description of the Related Art In order to obtain a large-screen television image, it has been well known that the television image is projected onto a relatively small picture tube and enlarged and projected onto the screen using a projection lens. Nowadays, due to improvements in the performance of picture tubes, projection lenses, and transmissive screens, there has been remarkable progress in projection television systems that place the optical system and circuitry inside the cabinet and project images from the front and back of the transmissive screen. ,
The projection lens is an all-resin lens with an aspherical surface.
It is highly resistant to changes in ambient temperature by using lenses composed of single lenses (for example, JP-A-55-124114, JP-A-57-34515, etc.), or by combining glass lenses and resin lenses as shown in Figure 3. 3-element lens (for example, Japanese Patent Application Laid-Open No. 58-118616, Japanese Patent Application Laid-Open No. 58-1
25007, etc.) have been proposed. Furthermore, recently, with the aim of making the depth of this type of projection television device extremely thin, a method has been proposed in which the light flux emitted from the projection lens enters the transmissive screen from a considerably oblique direction (for example, , Japanese Patent Publication No. 57-1094
Publication No. 81).

FIG. 4 shows a schematic configuration of such a projection television apparatus. A transmission type screen 2 is arranged on the upper front side of the cabinet 1, and a plane mirror 3 is arranged on the upper end.
A picture tube 5 is arranged at the bottom with the face plate 4 facing upward, and a projection lens 6 is arranged above the picture tube 5. The image projected on the picture tube 5 is enlarged and projected onto the screen 2 by the imaging action of the projection lens 6 and the reflection action of the plane mirror 3, but the light flux coming out of the projection lens 6 is from a direction quite oblique to the screen 2. Since the light is incident, the length of the plane mirror 3 in the depth direction is shortened, and the depth of the cabinet 1 can be made extremely thin.

As shown in FIG. 5, the screen 2 has minute prisms 7 having a triangular cross section and elongated horizontally arranged regularly on the back surface. The light ray 9 incident on the first surface 8 of the micro prism 7 passes through the first surface 8 and is totally reflected on the second surface 10, and the light ray 11 after total reflection becomes parallel to the normal 12 of the screen 2. . A light diffusing material is mixed inside the screen 2, and light is diffused within a suitable viewing angle range. In this way, even if light rays enter the screen 2 from a considerably oblique direction, the light ray bending and light diffusing effects of the micro prism 7 provide a bright projected image to the viewer located in front of the screen 2. can be provided. If a lenticular lens is provided on the viewer side surface 13 of the screen 2, the horizontal viewing angle range can be widened.

Problems to be Solved by the Invention In the projection television apparatus having the configuration shown in FIG. In order to focus and enlarge the entire surface of the image, the video tube 5 must also be tilted at an appropriate angle with respect to the optical axis 14, as shown in FIG. As shown in FIG. 3, the projection lens used in the projection television device is a plano-concave lens with a concave surface 15 having a large curvature facing the screen 2, located just in front of the face plate 4 of the picture tube 5. element 16
It has become common to have a configuration in which When using such a projection lens, if the distance between the lens element 16 and the face plate 4 is too short, the lens element 16 and the face plate 4 will come into contact with each other, and the image tube will be distorted with respect to the optical axis 14 of the projection lens 6. 5 cannot be arranged at a predetermined angle.

Therefore, it is conceivable to use a projection lens in which the distance between the lens element 16 and the face plate 4 is long, but it is difficult to properly correct aberrations with such a projection lens for the following reasons. The concave surface 15 of the plano-concave lens element 16 is intended to correct field curvature, and the concave surface 15 and the video tube 5
When the distance between the concave surface 15 and the phosphor surface 17 is short, the height of the axial ray passing through the concave surface 15 from the optical axis 14 is low, so that the concave surface 1
Even if the curvature of the concave surface 15 is large, the spherical aberration generated by the concave surface 15 is small, and the curvature of field can be effectively corrected. However, when attempting to lengthen the distance between the concave surface 15 and the phosphor surface 17, the height of the axial ray passing through the concave surface 15 from the optical axis 14 increases, which increases the spherical aberration that occurs on the concave surface 15, and the lens This makes it difficult to satisfactorily correct various aberrations of the entire system. To overcome this difficulty, it is necessary to increase the number of lenses and use a material with a high refractive index, making the projection lens expensive.

The present invention has been made in view of the above-mentioned problems, and allows the picture tube to be arranged at a predetermined angle with respect to the optical axis of the projection lens, thereby increasing the depth of the cabinet and improving image quality. The purpose is to provide a projection television device.

Means for Solving the Problems In order to solve the above problems, the projection television apparatus of the present invention includes an image display device, a projection lens disposed in front of the image display device, and a projection lens disposed in front of the image display device. a transparent material filled in a space between a lens element adjacent to the image display device and the image display device; the image display device is arranged at an angle of 3e or more with respect to the optical axis of the projection lens; The refractive index difference between the transparent material and the lens element is 0.
．． 3 or less, and the surface of the lens element on the image display device side is a convex surface or a substantially convex surface.

Effects According to the above configuration, since the surface of the lens element adjacent to the image display device of the projection lens on the image display device side is a convex surface or a substantially convex surface, the projection lens Even if the distance between the projection lens and the image display device is shortened, the image display device can be tilted by a predetermined angle with respect to the optical axis of the projection lens. In addition, since the refractive index difference between the lens element adjacent to the image display device of the projection lens and the transparent material is 0.3 or less, the aberrations generated at this interface are extremely small, and the aberrations of the entire lens system can be well corrected. This makes it possible to obtain a projected image with good image quality.

Embodiment An embodiment of a projection television apparatus according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a sectional view of a projection type television set according to an embodiment of the present invention, in which 1 is a projection lens, 19 is a screen, 20 is a video tube, and 21 is a lens adjacent to the video tube 20 of the projection lens 18. Element 22 is a transparent material. A screen 19 is disposed at a remote position in front of the projection lens 18 obliquely to the optical axis 23 of the projection lens 18, and a face plate 24 is disposed close to the rear of the projection lens 18 with a face plate 24 facing the projection lens 18 side. A picture tube 20 is arranged. Lens element 2 adjacent to the video tube 20 of the projection lens 18
A transparent material 22 is filled in the space between the video tube 1 and the face plate 24 of the picture tube 20. The picture tube 20 is arranged diagonally with respect to the optical axis 23 of the projection lens 18 so that the image projected on the phosphor surface 25 is focused and enlarged over the entire surface of the screen 19. .

For example, the angle between the optical axis 23 and the normal line 26 of the screen 19 is 60'', and the angle between the optical axis 23 and the tube axis 27 of the picture tube 2e is 15 degrees. The image is enlarged and projected onto the screen 19 due to the image formation effect of the projection lens 18, but since the light beam emitted from the projection lens 18 enters the screen 19 from a considerably oblique direction, the width of the light beam becomes small and the optical system is housed. The depth of the cabinet can be made very thin.

The lens element 21 has a lens surface 28 on the picture tube 20 side that is a spherical convex surface, and a surface 29 on the opposite side that is a concave surface, and has the function of correcting field curvature.

Since the lens surface 28 is a convex surface, even if the video tube 20 is tilted at a predetermined angle with respect to the optical axis 23, the distance from the concave surface 29 of the lens element 21 to the phosphor surface 25 measured on the optical axis 23 cannot be changed. Can be shortened. When the distance from the concave surface 29 to the phosphor surface 25 is short, the spherical aberration generated at the concave surface 29 is small, so that it is possible to correct the curvature of field and other aberrations in a well-balanced manner.

Incidentally, the difference in refractive index between the lens element 21 and the transparent material 22 is important. For example, if the transparent substance 22 is left in the air, new aberrations will be generated due to the difference in refractive index on both sides of the lens surface 28, so if the lens surface 28 is made a convex surface with a large curvature, it will be difficult to correct the aberrations. . However, lens element 2
When the refractive index of lens 1 and the transparent material 22 are exactly the same, no light rays are refracted at the interface between the two, so the shape of the lens surface 28 can be freely determined. Therefore, the transparent substance 22
If a material whose refractive index is close to that of the lens element 21 is selected, the refraction of light rays at the lens surface 28 will be very small, and various aberrations generated at the lens surface 28 will be small. You should be able to decide freely to some extent. Lens element 21 and transparent material 22
When acrylic resin and gel-like silicone resin are used as
0, and since the difference in refractive index between the two is small, good aberration correction is possible in this case. It seems that if this refractive index difference is 0.3 or less, good aberration correction is possible.

Other embodiments of the invention will be described below.

The lens surface 28 of the lens element 21 shown in FIG. 1 on the picture tube 20 side can be made into an aspherical convex surface, as shown in an enlarged view in FIG. This aspherical convex surface has a shape in which a peripheral portion 30 thereof is shifted in a direction away from the picture tube 20 with respect to a spherical surface 31 determined by the radius of curvature of the apex. When the picture tube 20 is tilted at a predetermined angle with respect to the optical axis 23, the distance between the lens element 21 and the face plate 24 measured on the optical axis 23 can be made shorter than when the lens surface 28 is a spherical surface. can. Therefore, the projection lens 18 can perform better aberration correction. Note that the lens surface 28 does not need to be a completely convex surface, and may be concave only near the apex.

When the angle between the tube axis 27 of the picture tube 20 and the optical axis 23 is small, the angle between the normal 26 of the screen 19 and the optical axis 23 is also small, so the depth of the cabinet is almost the same as before. The object of the invention is not achieved. In order to reduce the depth of the cabinet, the tube axis 2 of the picture tube 20 must be
7 and the optical axis 23 of the projection lens 8 is preferably selected to be 3'' or more.

Lens element 21 can be rotationally symmetrical like conventional lens elements. In general, rotationally symmetrical structures can be processed with high accuracy and easily, and are therefore convenient for processing lens elements. In particular, as can be seen from FIG. 1, the lens element 21 adjacent the picture tube 20 has a lens surface 28.
Since there is less variation in wall thickness than when the lens element 21 is a flat surface, the lens element 21 can be processed with high accuracy when resin molding is performed, and mass productivity is improved.

The picture tube 20 shown in FIG. 1 can be replaced with many other types of image display devices, such as a liquid crystal display. The intent of the present invention can be achieved no matter what image display device is used.

Effects of the Invention As described above, the present invention is a projection optical device that greatly reduces the depth of the cabinet by projecting the luminous flux emitted from the projection lens obliquely onto the screen. The distance between the lens element and the picture tube measured on the optical axis even if the picture tube side surface of the nearest lens element is made convex or almost convex and the picture tube is tilted at a predetermined angle with respect to the optical axis of the projection lens. Since it is possible to shorten the length, it is possible to perform good aberration correction, and it is possible to realize a projection optical device with good image quality, which has a very large effect.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a projection television apparatus according to an embodiment of the present invention, FIG. 2 is a sectional view of main parts of a projection television apparatus according to another embodiment, and FIG. 3 is a sectional view of a projection television apparatus according to another embodiment. FIG. 4 is a cross-sectional view showing the configuration of a conventional projection lens used, FIG. 4 is a cross-sectional view showing the configuration of a conventional projection television device, and FIG. 5 is a cross-sectional view showing the configuration of a screen used in the configuration shown in FIG. It is a diagram. 18...Projection lens, 19...Screen, 20...Picture tube, 21...Lens element, 22...Transparent substance. Name of agent: Patent attorney Toshio Nakao and one other person Figure 2 Figure 4

Claims (7)

[Claims] (1) An image display device, a projection lens arranged in front of the image display device, and a transparent material filled in a space between a lens element of the projection lens adjacent to the image display device and the image display device. the image display device is arranged at an angle of 3° or more with respect to the optical axis of the projection lens, the refractive index difference between the transparent medium and the lens element is 0.3 or less, and the lens A projection television apparatus, wherein a surface of the element on the side of the image display device is a convex surface or a substantially convex surface. (2) The surface of the lens element adjacent to the image display device on the side of the image display device is an aspheric convex surface or a substantially convex surface,
2. The projection television apparatus according to claim 1, wherein the peripheral portion thereof is shifted in a direction away from the image display device with respect to a spherical surface determined by a radius of curvature of the vertex. (3) The projection television apparatus according to claim (1), wherein the surface of the lens element adjacent to the image display device on the side opposite to the image display device is a concave surface. (4) The projection television device according to claim (1), wherein the lens element adjacent to the image display device is rotationally symmetrical. (5) The projection television device according to claim (1), wherein the lens element adjacent to the image display device is made of resin. (6) The projection television device according to claim (5), wherein the lens element adjacent to the image display device is made by resin molding technology. (7) The image display device is a video tube.
1) The projection television device described in item 1).