JPH0658492B2 - Image projection device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. 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 on a screen.

2. Description of the Related Art In order to obtain a television image on a large screen, a method of projecting a television image on a relatively small picture tube and enlarging and projecting it on a screen by a projection lens has been well known. Recently, a method has been proposed in which the depth of a television image projection device is made extremely thin by causing a light beam emitted from a projection lens to enter the screen in an oblique direction (for example, JP-A-57-109481). ).

FIG. 8 shows a schematic configuration of such a television image projection apparatus. In the figure, a screen 2 is arranged on the front side of the upper part of the cabinet 1, a plane mirror 3 is arranged on the upper part inside thereof, a picture tube 4 is arranged on the lower part thereof, and a projection lens 5 is arranged above the picture tube 4. ing. Then, the image projected on the picture tube 4 is caused by the image forming action of the projection lens 5 and the plane mirror 3
It is projected on the screen 2 in an enlarged manner by the reflection of. Here, as shown in the figure, since the light flux emitted from the projection lens 5 is projected from the screen 2 in a considerably oblique direction,
The length of the plane mirror 3 in the depth direction becomes short, and the depth of the cabinet 1 can be made very thin.

As shown in FIG. 9, the screen 2 has a triangular cross-section on the back surface, and elongated fine prisms 6 are regularly arranged in the horizontal direction. The light ray 8 incident on the first surface 7 of the minute prism 6 is transmitted through the first surface 7 and then totally reflected by the second surface 9, and the light ray 10 after the total reflection is the normal line of the screen 2.
It will be parallel to 11. Since a light diffusing material is mixed inside the screen 2 and diffuses light within a range of an appropriate viewing angle, it is possible to provide a bright projection image to an observer located in front of the screen 2. It has become.

Problems to be Solved by the Invention However, in the above-mentioned configuration, since the projection light beam is projected obliquely to the image forming medium, when the projection lens 5 has a normal rotationally symmetric configuration, The image to be displayed on the video tube 4 is a trapezoidal image as shown by the solid line 12 in FIG. In the figure, the broken line 13 indicates the region of the phosphor surface of the picture tube 4, and the aspect ratio is approximately 3: 4. As can be seen from FIG. 10, the length in the vertical direction is short, and the area of the unused portion on the phosphor surface is large. Since there is an upper limit to the amount of light emission per unit area on the phosphor surface, there is a problem that if the utilization rate on the phosphor surface is small, the projected image on the screen 2 becomes darker. .

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

Means for Solving the Problems In order to solve the above problems, the image projection apparatus of the present invention is
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, and the triangular prism is an object image of the lens system. To the screen, the projection light flux emitted from the lens system or the triangular prism is projected obliquely to the screen.

In the present invention, in the above-described configuration, by using a lens system having different focal lengths in the vertical and horizontal directions of the projected image as the projection lens, the projection magnification can be changed in the vertical and horizontal directions of the projected image. , When the projected light flux is projected obliquely to the screen, the image can be approximated to a rectangle, and the utilization factor of the phosphor surface of the picture tube can be improved, so that the brightness of the projected image is improved. be able to. In this case, since the projected light beam is projected obliquely to the screen, a new problem occurs in which the vertical and horizontal image planes do not coincide, that is, the astigmatic difference occurs. Utilizing the fact that the triangular prism has a property of generating astigmatic difference, at least 1 is provided in the optical path from the object image to the screen.
By arranging two triangular prisms, this triangular prism intentionally generates an astigmatic difference of an appropriate size, and the astigmatic difference generated by projecting obliquely to the screen is canceled. It is possible to reduce the astigmatic difference and to obtain a projected image of good quality over the entire screen.

Embodiments Embodiments of the projection optical apparatus of the present invention will be described below with reference to the drawings.

FIGS. 1 (a) and 1 (b) show an embodiment of the present invention, showing a vertical cross section and a horizontal cross section including the optical axis, respectively, and FIG. 1 (b) shows a bent optical axis. Is shown in a straight line. From the screen 14 side, a triangular prism 15, a lens system 16, and a picture tube 17 are arranged relatively close to each other. The focal length in the vertical section of the lens system 16 is longer than the focal length in the horizontal section. The vertical cut surface corresponding to the paper surface of FIG. 1 (a) is the only symmetrical surface of the entire optical system. The screen 14 is arranged to be inclined with respect to the projection optical axis 18,
Of the rays incident on the center 19 of the screen 14, the screen
The triangular prism 15 is arranged such that the light ray having a larger angle that is the normal line 20 of 14 has a longer distance to pass through the triangular prism 15. The face plate 21 of the picture tube 17 is also the lens system 16
The image tube 17 is arranged so that the screen 14 and the face plate 21 are inclined in the opposite directions and have a V shape.

The lens system 16 is, as shown in FIGS. 1A and 1B, a rotationally symmetric lens system 23 arranged on the side of the picture tube 17.
And a non-rotationally symmetric lens system 24 arranged on the screen 14 side. Non-rotationally symmetric lens system 24 is 2
The lens 25 on the side of the screen 14 has a surface 26 facing the screen 14 is a convex cylindrical surface with a generatrix in the horizontal direction, and a surface 27 on the reflection side is a flat surface.
On the other hand, in the lens 28 on the side of the video tube 17, the surface 29 facing the screen 14 is a flat surface, and the surface 30 on the reflection side is a concave cylindrical surface with the generatrix in the horizontal direction. The focal length in the horizontal direction of the non-rotationally symmetric lens system 24 is infinite, and the focal length in the vertical direction is set to infinity or sufficiently longer than the focal length of the rotationally symmetric lens system 23. Here, the angular magnification seen on the side of the picture tube 17 is 1 in the horizontal direction and larger than 1 in the vertical direction due to the action of the two lenses and the cylindrical surfaces 26, 30 of the 25, 28.

Next, the operation of the above-described first embodiment will be described. The combined focal length of the lens system 16 that combines the rotationally symmetric lens system 23 and the non-rotationally symmetric lens system 24 is the angular magnification and rotational symmetry when parallel rays are incident on the non-rotationally symmetric lens system 24 from the screen 14 side. Since it is represented by 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 lateral magnification seen from the video tube 17 side is larger in the vertical direction than in the horizontal direction. Therefore, the image to be displayed on the video tube 17 can be an image having the shape shown by the solid line 31 in FIG. The broken line 32 indicates the area of the phosphor surface of the picture tube 17, and the aspect ratio is approximately 3: 4. Compared with the shape of the image to be displayed on the picture tube when the ordinary rotationally symmetric projection lens shown in FIG. 10 is used, the shape shown by the solid line 31 in FIG. Only the area is getting bigger. Therefore, if the amount of light emission per unit area of the phosphor surface is constant, the brightness of the projected image can be improved as much as the used area on the phosphor surface is increased.

By the way, in the configuration shown in FIG.
If there is no 15, the following problems occur. When using a lens system 16 having different focal lengths in the vertical direction and the horizontal direction, when the projection light beam is projected obliquely to the screen 14, the image on the side of the video tube 17 on the vertical section plane including the optical axis is very sharp. It produces a large astigmatic difference. FIG. 3 shows an example of vertical astigmatism seen on the side of the picture tube 17, and the vertical axis shows the upper and lower image heights with the center 33 of the picture tube 17 as the origin. The horizontal axis indicates the aberration in the optical axis direction. The solid line represents the sagittal direction and the broken line represents the meridional direction. As is clear from FIG. 3, both the solid line and the broken line are linear, but the directions in which the astigmatic difference appears at the top and bottom are opposite. This occurs because the focal length of the lens system 16 differs in the vertical direction and the horizontal direction, and the more the focal lengths in the vertical direction and the horizontal direction shift, the more the angle between the normal line 20 of the screen 14 and the projection optical axis 18 becomes. As becomes larger, the astigmatic difference appears more significantly. Since the astigmatic difference appears in the upper and lower directions, and even if the astigmatism of the lens system 16 is corrected, the two astigmatism curves move in the same direction in the upper and lower directions. The astigmatic difference shown in the figure cannot be corrected. Therefore, in order to correct the astigmatic difference as shown in FIG. 3, it is expected that an optical system asymmetrical above and below the vertical section plane including the optical axis is required.

Next, the operation of the triangular prism 15 shown in FIG. 1 will be described. As shown in FIGS. 4 (a), (b), and (c),
Consider astigmatism on a vertical cut surface by the triangular prism 15 arranged on the normal 20 of the screen 14. Here, two optical axes 34 and 35 are defined on both sides of the triangular prism 15, the optical axis 34 coincides with the normal line 20 of the screen 14, and the light rays incident on the triangular prism 15 along the optical axis 34 are triangular prisms. 15
After exiting, it shall proceed along the optical axis 35. 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 figure (b) shows the same when the surface 37 of the triangular prism 15 on the side far from the screen 14 is perpendicular to the optical axis 35. Figure (c) shows the normals 38 and 39 on both sides of the triangular prism 15 and the optical axes 34 and 35.
Shows the case where the respective angles are the same on both sides.
Astigmatisms in the configurations shown in FIGS. 4A, 4B, and 4C are shown in the characteristic diagrams of FIGS. 4D, 4E, and 4F, respectively. It can be seen that the use of the triangular prism 15 produces a straight line or an astigmatism close to a straight line that is vertically asymmetric. When the triangular prism 15 is replaced by a parallel plane, the astigmatism generated is very small. It can be seen that it depends on the corner. Also, the astigmatic difference at the origin differs depending on how the triangular prism 15 is arranged.
It can also be seen that the astigmatic difference at the center of 14 can be corrected.
From the above, it is understood that the astigmatic difference as shown in FIG. 3 which is generated in the lens system 16 as shown in FIG. 1 can be corrected by the triangular prism 15. That is, the astigmatism on the side of the video tube 17 of the optical system shown in FIG. 1 can be corrected to the characteristic shown in FIG. 5, and the phosphor surface is shown on the curve shown in FIG. The video tubes 17 may be arranged so as to overlap each other.

Next, another embodiment of the present invention will be described.

FIGS. 6 (a) and 6 (b) show another embodiment of the present invention, which shows a vertical section and a horizontal section including the optical axis, respectively. In this embodiment, the difference from the configuration shown in FIGS. 1A and 1B is that the triangular prism
15 is arranged between the rotationally symmetric lens system 23 and the non-rotationally symmetric lens system 24, and the configuration of each component is the same as that shown in FIGS. 1 (a) and 1 (b). The rotationally symmetric lens system 23 and the non-rotationally symmetric lens system 24 are arranged so as to be inclined, and a ray traveling along the optical axis 22 of the rotationally symmetric lens system 23 is refracted by the triangular prism 15 and then the non-rotationally symmetric lens system 24. It is designed to travel along the optical axis 40 of. FIG. 6 (a),
Even with the configuration shown in FIG. 7B, the astigmatic difference generated in the non-rotationally symmetric lens system 24 can be corrected by the triangular prism 15.

Also, two triangular prisms can be used. For example, the first triangular prism is arranged between the screen 14 and the lens system 16 as shown in FIG. 1, and the second triangular prism is arranged inside the lens system 16 as shown in FIG. is there. It should be noted that the triangular prism is preferably arranged at a position where the light flux emitted from the center of the picture tube becomes nearly parallel.

FIG. 7 shows another embodiment of the present invention in which two triangular prisms are used and one surface of each triangular prism is curved. A rotationally symmetric lens system 23 is arranged in front of the video tube 17, a triangular prism optical system 41 is arranged in front of the rotationally symmetric lens system 23, and a screen 14 is further arranged in front of it. The triangular prism optical system 41 is composed of a first triangular prism 42 and a second triangular prism 43.
The surface 44 of the triangular prism 42 on the side of the picture tube 17 is a concave cylindrical surface with the generatrix oriented in the vertical direction, and the surface 45 of the second triangular prism 43 on the screen 14 side is a convex with the generatrix oriented in the vertical direction. It has a cylindrical surface.

Even in the configuration shown in FIG. 7, the image to be displayed on the picture tube 17 can be formed into a shape compressed in the horizontal direction by the two cylindrical surfaces 44 and 45, and the outside of the two triangular prisms 42 and 43 can be formed. Since the surfaces 46 and 47 function as a prism, the astigmatic difference can be reduced.

Further, in the configuration shown in FIG. 7, the two surfaces 44, 45 are not limited to the cylindrical surfaces, and the focal lengths may be different in the vertical direction and the horizontal direction. For example, the shape may be an ellipsoidal surface. Furthermore, the outer surfaces 46 and 47 of the triangular prism optical system 41 are gently curved,
It is also possible to change the focal length in the vertical direction and the horizontal direction.

EFFECTS OF THE INVENTION As described above, according to the present invention, the projection light beam screen is projected in an oblique direction, and the projection lens is a lens system having different focal lengths in the vertical direction and the horizontal direction of the projected image. By doing so, the phosphor surface of the picture tube can be effectively used, and thus a projected image with higher brightness can be obtained. Further, since the astigmatic difference generated in the lens system can be corrected by the triangular prism, it is possible to obtain a projected image of good quality over the entire screen. Further, since the projected light flux is projected obliquely to the screen, the depth of the device can be made very short.

[Brief description of drawings]

1 (a) and 1 (b) are vertical and horizontal cross-sectional views showing the configuration of an image projection apparatus in an embodiment of the present invention, and FIG. 2 is an image with the configuration shown in FIGS. 1 (a) and 1 (b). A diagram showing the shape of the image to be projected on the tube, FIG. 3 is a characteristic diagram showing astigmatism on the image tube side in the case where the triangular prism is not provided in the configuration of FIG. 1, FIGS. 4 (a) and 4 (b). ), (C) and (d),
6 (e) and 6 (f) are configuration diagrams and characteristic diagrams for explaining the operation of the triangular prism, FIG. 5 is a characteristic diagram showing astigmatism of the configuration shown in FIG. 1, and FIG. 6 (a). , (B) and FIGS. 7 (a) and 7 (b) are vertical and horizontal sectional views showing the configuration of another embodiment of the present invention, FIG. 8 is a sectional view showing the configuration of a conventional example, and FIG. FIG. 8 is a sectional view showing the structure of the screen used in the structure shown in FIG. 8, and FIG. 10 is a diagram showing the shape of the image to be displayed on the picture tube in the structure shown in FIG. 14 ... Screen, 15, 42, 43 ... Triangular prism, 16 ... Lens system, 17 ... Video tube

Claims (5)

[Claims] 1. A lens system having different focal lengths in a vertical direction and a horizontal direction of a projected image in an optical path between a picture tube and a screen, and at least one triangular prism. An image projection apparatus arranged in an optical path from an object image of a lens system to a screen, and projecting a projection light flux emitted from the lens system or the triangular prism from an oblique direction to the screen. 2. The image projection apparatus according to claim 1, wherein there is only one plane of symmetry of the optical system including the lens system and the triangular prism. 3. The image projection apparatus according to claim 2, wherein the focal length of the lens system becomes maximum in the direction along the plane of symmetry. 4. Of the light rays incident on the center of the screen,
The image projection apparatus according to claim 1, wherein the triangular prism is arranged such that a light ray having a larger angle with a normal line of the screen has a longer distance to pass through the triangular prism. 5. The image projection apparatus according to claim 1, wherein at least one surface of the triangular prism is a curved surface.