JPS61275831A - Image projector - Google Patents

Abstract

PURPOSE:To improve the utilization rate of the fluorescent material surface of a video tube and to enlarge and to project a projection image with good picture quality and high brightness by using a lens system which is different in focal length in the vertical and horizontal directions of the projection image as a projection lens. CONSTITUTION:The composite focal length of the lens system 16 composed of a rotationally symmetrical lens system 23 and a rotationally asymmetrical lens system 24 in combination is expressed by the product of angular magnification when a parallel light beam is incident on the rotationally asymmetrical lens system 24 from the side of a screen 14 and the focal length of the rotationally symmetrical lens system 23, so the vertical composite focal length is longer than the horizontal composite focal length. Consequently, an image to be projected on the video tube increases in area by an vertical increase in length as compared with an image to be projected on the video tube when a normal rotationally symmetrical projection lens is used, so when the quantity of emitted light per unit area of the fluorescent material surface is assumed to be constant, the brightness of the projection image is improved by the increase in the utilized area on the fluorescent material surface. In such a case, the astigmatic difference of the lens system 16 is compensated by a triangular prism 15.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image projection apparatus for enlarging and projecting an image projected on a relatively small picture tube onto a screen.

2. Description of the Related Art In order to display 1 q of large-screen television images, it has been well known that the television image is projected onto a relatively small picture tube and then enlarged and projected onto the screen using a projection lens. Recently, a method has been proposed in which the depth of a television image projection device is made extremely thin by making the light flux emitted from the projection lens incident on the screen from a considerably oblique direction.
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The schematic structure of such a television image projection device is shown in FIG. A screen 2 is placed on the front side of the same net 1, a plane mirror 3 is placed on the inside thereof, a video tube 4 is placed at the bottom, and a projection lens 5 is placed on one side of the video tube 4. are doing. The image projected on the video tube 4 is enlarged and projected onto the screen 2 by the imaging action of the projection lens 5 and the reflection from the plane mirror 30. Here, as shown in FIG. 16, since the light beam emitted from the projection lens 5 is projected onto the screen 2 from a considerably oblique direction, the length of the plane mirror 3 in the convex direction is shortened.
The depth of the cabinet 1 can be made very thin.

1- As shown in FIG. 9, the screen 2 has minute prisms 6 having a triangular cross section and elongated horizontally arranged regularly on the back surface. The 107th minute prism 6
After passing through the first surface 7, the light ray 8 entering the screen is totally reflected on the second surface 9, and the reflected light ray 10 is reflected by the normal 11 of the screen 2 and the surface ti. ru. A light diffuser (4) is mixed inside the screen 2, which diffuses light in an appropriate <p viewing angle range.゛I]'' Providing the image has become (Passal J-un).

Problems solved by the invention However, in the configuration as described in -1-, the projection 7,1 light beam is projected onto the imaging medium from the diagonal/i direction.
Therefore, when the projection lens 5 has a normal rotationally symmetrical configuration, the image that should be projected onto the picture tube 4 is a trapezoidal image shown by the solid line 12 in FIG.

In the same figure, the broken line 13 is the t of the phosphor surface of the EIFIA Shin 4.
It shows area II, and the aspect ratio is 3:4.

As can be seen from FIG. There is a limit to the amount of light emitted by the screen 21.
The problem of it being dark is a good thing. .

-41 In view of the above-mentioned problems, the present invention provides an image projection device that improves the utilization rate of the phosphor surface of a picture tube and can enlarge and project a projected image with high brightness and good image quality. .

Means for Solving the Problems F In order to solve the problems, the image projection 8Fl of the present invention has a focal length in the vertical and horizontal directions of the projected image in the optical path between the picture tube and the screen. and at least one triangular prism, the triangular prism is arranged in an optical path from the object image of the lens system to the screen, and the projection light beam exiting from the lens system or the triangular prism is is projected diagonally onto the screen.

Function The present invention uses a lens system having a different focal length in the vertical and horizontal directions of the projected image in the configuration described in I, as the projection lens, so that the projection magnification can be adjusted in the vertical and horizontal directions of the projected image. Since it can be changed, when the projected image is projected from an oblique direction to the screen, the image can be made closer to a rectangle, and the utilization rate of the phosphor surface of the picture tube can be increased by 1. Therefore, the brightness of the projected image can be changed in one direction. In this case, the projection light is projected diagonally to the screen.
When the imaging planes of vertical and horizontal lines coincide, a phenomenon occurs, in other words, an astigmatism difference occurs (an opening angle of I/i 1 = 1 occurs), but the triangular prism does not have an astigmatism difference. Taking advantage of this property, at least 61 triangular prisms are arranged in the optical path between the object image and the screen, and the triangular prisms generate an appropriately large astigmatism difference in II@. Projecting from an oblique direction to the screen (in order to avoid canceling out the astigmatism difference), it is possible to reduce the astigmatism difference of the entire device, This makes it possible to obtain a projected image of good C0 quality over the entire screen.

Embodiments Hereinafter, embodiments of the projection optical device of the present invention will be explained with reference to the drawings.

= 6 - Figures 1(a) and 1(b) show an embodiment of the present invention, and show the configuration of a vertical cross section and a horizontal cross section including the optical axis, respectively. The optical axis is shown stretched out in a straight line. A triangular prism 15, a lens system 16, and a video tube 17 are arranged relatively close to each other in order from the screen 14 side. The focal length of the lens system 16 in the vertical section is longer than the focal length in the horizontal section. The vertical cut plane corresponding to the plane of the paper in FIG. 1(a) is the only plane of symmetry of the entire optical system. The screen 14 is arranged at an Iff angle with respect to the projection optical axis 18, and among the light rays incident on the center 19 of the screen 14, the larger the normal angle 20 to the screen 14, the more the rays pass through the triangular prism 15. The triangular bridge 1815 is arranged so that the distance between

The face plate 21 of the picture tube 17 is also inclined with respect to the optical axis 22 of the lens system 16, and the picture tube 17 is arranged so that the screen 14 and the 7-eighth plate 21 are inclined in opposite directions to form a V-shape. It is located.

As shown in FIGS. 1(a) and 1(b), the lens system 16 includes a rotationally symmetrical lens system 23 placed on the side of the picture tube 17, and a non-rotating lens system 23 placed on the side of the screen 14. It consists of a symmetrical lens system 24.

The non-rotationally symmetrical lens system 24 is composed of two lenses, and the lens 25 on the screen 14 side is
26 is a convex cylindrical surface with its generatrix oriented horizontally, and 21 on the opposite side is a flat surface. On the other hand, video tube 1
In the lens 28 on the side 7, the surface 29 facing the screen 14 is flat, and the surface 30 on the reflective side is a concave cylindrical surface with the generatrix oriented horizontally.This non-rotationally symmetric lens system 24
The focal length in the horizontal direction is infinite, and the focal length in the vertical direction is set to be infinite or sufficiently better than the focal point v1 of the rotationally symmetrical lens system 23. Here, the angular magnification seen from the picture tube 17 side is the cylindrical surface 26 of the two lenses 25 and 28.
．． Due to the action of 30, the horizontal direction is 1 and the vertical direction is greater than 1.

Next, the operation of the first embodiment described above will be explained. The composite focal length of the lens system 16, which is a combination of the rotationally symmetric lens system 23 and the non-rotationally symmetric lens system 24, is rotationally symmetric with the angular magnification when a parallel ray is incident on the non-rotationally symmetric lens system 24 from the screen 14 side. Since it is expressed as the product of the focal lengths of the lens system 23, the combined focal length in the vertical direction is longer than that in the horizontal direction.

Further, the horizontal magnification when viewed from the picture tube 17 side is greater in the vertical direction than in the horizontal direction. Therefore, the image to be displayed on the video tube 17 can be shaped as shown by the solid line 31 in FIG. Note that the broken line 32 indicates the region of the phosphor surface of the picture tube 17, and its aspect ratio is approximately 3:4. Compared to the shape of the image projected onto the picture tube when a normal rotationally symmetrical projection lens is used as shown in FIG. 10, the shape shown by the solid line 31 in FIG. 2 is improved in the vertical direction. The area is only larger. Therefore, if the luminescence age per unit area of the phosphor surface is constant, the brightness of the projected image can be improved as the usable area on the phosphor surface increases.

By the way, in the configuration shown in FIG. 1, if the triangular prism 15 is not provided, the following problem will occur. When using a lens system 16 with different focal lengths in the vertical and horizontal directions, if the projected light beam is projected onto the screen 14 from an oblique direction, the image on the picture tube 17 side on the vertical cut plane including the optical axis will be very distorted. Lights a large astigmatism difference. FIG. 3 shows an example of vertical astigmatism seen from the picture tube 17 side, and the vertical axis indicates the upper and lower image heights with the center 33 of the picture tube 17 as the origin. The horizontal axis indicates aberration in the optical axis direction. The solid line indicates the characteristic in the sagittal direction, and the broken line indicates the characteristic in the meridional direction. As is clear from FIG. 3, both the solid line and the broken line are straight lines, but 1. At the bottom, the astigmatic difference appears in the opposite direction. This occurs because the focal point 91 m of the lens system 16 is different in the vertical and horizontal directions, and the focal lengths in the vertical and horizontal directions are different, and the normal 20 of the screen 14 and the projection optical axis 1 are different.
The more unusual the nozzle angle of 8, the more likely the astigmatism difference will appear.

The astigmatism f4 difference is expressed in the opposite way between the upper and lower sides, and even if the astigmatism of the lens system 16 is corrected, the two astigmatism curves will move in the same direction both above and below, so the lens system 16 Third
It is not possible to compensate for the astigmatism difference 1T-4 as shown in the figure. Therefore, the astigmatism difference as shown in FIG.
It is expected that an asymmetric optical system will be required with a perpendicular cutting plane that includes the optical axis.

Next, the vertical prism 15 shown in FIG. 1 for use in a pipe will be explained. As shown in FIGS. 4(a), (b), and (C), consider the astigmatism that occurs in the vertical cut plane of the triangular prism 15 placed on the normal line 20 of the screen 140.Here, 2 on both sides of the triangular prism 1115
The light rays that define two optical axes 34, 35, and that the optical axes 34 G, L coincide with the normal 20 of the screen 14 and enter the diagonal prism 15 along the optical axis 34 after exiting the triangular bridle 1115 It is assumed that the beam moves along the optical axis 35 by -C. Figure 4(a)
When the surface 36 of the triangular prism 15 on the screen 14 side is perpendicular to the optical axis 34, the same figure ([)] shows the case where the surface 37 of the 71-angle prism 15 on the side far from the screen 14 is heavier than the optical axis 35. The table (C) is ':: Square pre-prism 1
A case is shown in which the normals 38 and 39 of the five surfaces and one angle of each of the optical axes 34 and 35 are the same on both surfaces. This figure 4 (a
), (b), and (cl) show the astigmatism of the virtual image in the same figure (
-11= is shown in the characteristic diagrams of d), (e), and (f), and from this characteristic diagram 1 no 1 = 16-7 rhythm 1;
) to use t(2J,su,11・Asymmetrical and straight!
, = gives off an astigmatism X that is close to a straight line. I know what to do. ÷ angle - 1 rhythm 1! ) in 1 line, and in this case, the difference in point distance between light/1 and J1 is always small (゛,
- Ushikakuzo Rhythm 1! + It, 23j, the generated astigmatism difference enters the H-angle prism 15 (4) 1 ray and the triangle -
It can be seen that it depends on the polarization angle of the light beam exiting from the l-resist 15. Well, the difference between JL +'a and the origin is
Due to the fact that it is difficult to use the triangular prism, it is necessary to compensate for the astigmatism difference in the center of the rescreen 14. [It can also be seen that it can be done. From the above 1, as shown in Figure 1 1J, ``, Una lens thread 1 fi ``From C! Complementary 11 by triangular prism 15
(・You can see that it can be done.)
Figure 5 shows the astigmatism on the image 9 to 17 side of the optical system.
J, It is C-Sarushinogu to supplement Umu special bamboo,
Curve 1 shown in the same figure (the video tube 17 is placed so that the phosphor surface is parallel to the curve).

Next, another embodiment of the present invention will be explained, FIG.
Figures a) and (b) show other embodiments of the present invention, and show the configurations of a vertical cross section and a horizontal cross section including the optical axis, respectively. In this example, Fig. 1 (a>, (b)
The difference from the configuration shown in FIG.
It is the same as shown in b). Rotationally symmetric lens system 23
and the non-rotationally symmetrical lens system 24 are arranged obliquely,
After the light rays traveling along the optical axis 22 of the rotationally symmetric lens system 23 are refracted by the triangular prism 15, the light rays are refracted by the triangular prism 15, and then the non-rotationally symmetric lens system 24
C along the optical axis 40 of. Figure 6 (a
) and (b), the non-rotationally symmetric lens system 24
The triangular prism 15 can correct the astigmatism difference that occurs.

Moreover, a 2 m triangular prism can also be used.

For example, a first triangular prism may be placed between the screen 14 and the lens system 16 as shown in FIG. 1, and a second triangular prism may be placed inside the lens system 16 as shown in FIG. be. It is preferable to place the triangular prism in a location where the light beams emitted from the center of the picture tube are nearly parallel.

FIG. 7 shows a configuration of still another embodiment in which two triangular prisms are used and the -1 side of each triangular prism is curved. A rotationally symmetrical lens system 23 is arranged in front of the picture tube 17, a triangular prism optical system 41 is arranged in front of this rotationally symmetrical lens system 23, and further ^if
A screen 14 is placed at h. The triangular prism optical system 41 is composed of a first triangular prism 42 and a second triangular prism 43, and the video tube 17 of the first triangular prism 42
The surface 44 on this side is a concave cylindrical surface with the generatrix oriented vertically, and the surface 45 of the second triangular prism 43 on the screen 14 side is a convex cylindrical surface with the generatrix oriented vertically.

Even in the configuration shown in FIG. 7, the image that should not be projected onto the picture tube 17 can be compressed in the horizontal direction by the two cylindrical surfaces 44 and 45, and the two moly prisms 42 and 45 can compress the image in the horizontal direction.
Since the elements 46 and 47 on the outside of 43 act as prisms, the astigmatism difference can be made small.

In addition, in the configuration shown in FIG.
5 is not limited to a cylindrical surface, but may have a structure that takes care of the focal length in both the heavy direction and the horizontal direction. For example, the shape may be an ellipsoid 161. In history,
It is also possible to make the outer surfaces 46 and 47 of the triangular prism optical system 41 into gently curved surfaces so that the focal length can be changed in the vertical and horizontal directions.

According to the present defense, the projection light beam is projected from an oblique direction to the projection screen, and the projection lens has different focal lengths in the vertical and horizontal directions of the projected image. By using a lens system, the phosphor surface of the picture tube can be used effectively, making it possible to obtain a projected image with higher brightness. In addition, the astigmatism difference that occurs in the lens system can be corrected using a triangular prism.
A projected image of good quality can be obtained over the entire screen. Furthermore, since the projection light beam is projected obliquely to the screen, the projection of the device can be made very short.

4, 1￥1 side simple 11. /-; Explanation FIGS. 1(a) and 1(b) show the configuration of an image projection device according to an embodiment of the present invention.
Figure 2 1.1 Figure 1 (a>, (b) shows the shape of the image projected on the video tube in the 1. /j configuration. Figure 3 shows the configuration of Figure 1. Figure 4 shows the astigmatism on the imaging side when there is no triangular prism.
1, f-me and (d), (e).

([) are respectively a configuration diagram and a characteristic diagram to explain the action of the -i-angle prism, Figure 5 shows the astigmatism of the configuration with two prisms compared to Figure 1, Figure f1, and Figure 6. (a).

0) and FIGS. 7(a) and 7(b) are vertical and horizontal sectional views of the configuration of other embodiments of the present invention, and FIG. Figure 9 shows the configuration of the screen used in the configuration shown in Figure 8. Figure 10 shows the configuration of the screen used in the configuration shown in Figure 8. It is a diagram.

14...Screen, +5.42.43...Triangular prism, 16...Lens system, 17...Video control agent Yoshihiro Morimoto Figure 2Figure 2

Claims (1)

[Claims] 1. In the optical path between the picture tube and the screen, a lens system having different focal lengths in the vertical direction and the horizontal direction of the projected image and at least one triangular prism are provided; An image projection device, wherein a prism is disposed in an optical path from an object image of the lens system to a screen, and a projection light beam coming from the lens system or the triangular prism is projected onto the screen from an oblique direction. 2. The image projection device according to claim 1, wherein there is only one plane of symmetry of the optical system consisting of a lens system and a triangular prism. 3. The image projection device according to claim 2, wherein the focal length of the lens system is maximum in the direction along the plane of symmetry. 4. The triangular prism is arranged so that among the light rays incident on the center of the screen, the light having a larger angle with the normal line of the screen has a longer distance to pass through the triangular prism. Image projection device. 5. The image projection device according to any one of claims 1 to 4, wherein at least one surface of the triangular prism is curved.