JPH0427911A - Oblique projection display device - Google Patents

Abstract

PURPOSE:To prevent incorrect magnification of the image on a screen to improve the quality of the image by providing a lens which has a magnifying power and magnifies the reduction image formed by a first optical system to form an image on the screen. CONSTITUTION:A light valve 7 is set at a required angle to an optical axis 13 of a first optical system 8, and an image forming face 9 is inclined to the opposite side to the light valve with respect to the optical axis 13 and is set in the position where the image of the light valve 7 due to a reduction lens 11 of the first optical system 8 is formed. The first optical system 8 and a magnifying lens of a second optical system which has an optical axis bending to the optical axis of the first optical system 8 in the image forming face 9 are arranged with the image forming face 9 between them. The image on the image forming face 9 is magnified through the second optical system 10 and is magnified and obliquely projected on a screen 3 inclined to the opposite side to the image forming face 9. As the result, the trapezoidal distortion and the incorrect magnification of the magnified image formed on the screen are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an oblique projection display device, and more particularly to an oblique projection display device suitable for enlarging and projecting video images, computer images, and the like.

(Prior Art) Recently, display devices using transmissive or reflective dot matrix liquid crystals (hereinafter referred to as light valves) have been used to enlarge and project images displayed on the light valves onto a screen as a large screen. An enlarged projection method that shows images is attracting attention.

This is because there is a natural limit to the size of image display using a cathode ray tube (CRT), and increasing the screen size requires increasing the size of the cathode ray tube itself, and in practical terms, the maximum size is about 40 inches, so anything larger than that is necessary. This is to meet the demand for obtaining images of.

On the other hand, in order to increase the area of the light valve itself, it is not easy to obtain a large-sized liquid crystal display device that is free from manufacturing defects, and even if it could be obtained, it would be extremely expensive.

For this reason, if you use a transmissive (or reflective) light bulb to enlarge and project the image displayed on it, you will be able to get an impressive large screen without being restricted by the screen size. It is possible.

Therefore, an optical system for enlarging and projecting images using a light valve is housed inside the cabinet, and the rear projection is performed on a screen installed in the front of the cabinet so that the enlarged image can be viewed from the front of the cabinet. It has now been provided.

Conventional rear projection display devices using this type of light valve provide illumination from a light source to a transmissive liquid crystal panel, and the image displayed on this liquid crystal panel is disclosed in, for example, Japanese Utility Model Application Publication No. 1-85778. The structure is such that the light is magnified by a projection lens, the optical path is changed by a reflecting mirror, and the light is guided to the back of the screen. By doing this, the entire projection optical system is housed within the cabinet, allowing it to be moved to any location, and allowing images on the screen to be viewed even in a bright room.

However, in the above-mentioned conventional display-type rear projection display device, the light flux that passes through the light valve is converted into an optical path by a reflecting mirror and guided to the back of the screen, so it is necessary to project the light with the optical axis perpendicular to the screen. Since image distortion occurs due to keystone distortion, etc., there are significant restrictions on the installation conditions of the reflecting mirror, and this increases the volume occupied by the projection optical system, especially the depth dimension (cabinet thickness) relative to the screen. , it cannot be made into a rear projection type display device due to the prodigal type cabinet.

Therefore, an oblique projection method can be considered as a means to solve this problem. In this oblique projection method, as shown in FIG. 13, a second lens e having an optical axis d bent at an imaging plane C (for example, a reflecting means) with respect to the optical axis of the second lens a is attached to the imaging plane C. C is placed between them, and the second lens a and the second lens e
and are arranged in a "C" shape. The second lens e obliquely projects the image formed on the image plane C by the second lens a onto a screen S that is arranged at an angle opposite to the inclination of the image plane C with respect to the optical axis d. to obtain an enlarged image. In this case, if the optical path from the second lens e to the screen S is bent by a reflecting mirror and guided to the back of a screen provided on the front of the cabinet, a display device using rear projection can be created as a compact optical system. can get.

(Problem to be Solved by the Invention) However, when a display device that performs magnified projection is configured using the projection optical system described above, trapezoidal distortion occurs in the image formed on the imaging plane C by the lens a, and this distortion is When correcting the trapezoidal distortion using the second lens e and forming the image on the screen S, the image becomes a vertically elongated rectangle, resulting in a so-called elongated image, resulting in an unsightly image and not being able to provide faithful reproducibility. .

In view of this, it is an object of the present invention to provide an oblique projection display device that uses an oblique projection optical system and does not cause an image to be elongated on the screen when obtaining a large screen with a compact configuration. It was made for the purpose of

(Means for Solving the Problems) As a means for solving the problems of the above-mentioned prior art, the present invention provides a method for reducing the original image by arranging the original image at a predetermined angle with respect to the surface of the original image that can transmit or reflect light. a first optical system having a lens with a reduction magnification that forms an image; an imaging plane disposed at the imaging position of the first optical system; and an imaging plane that enlarges the reduced image formed on the imaging plane. The projection optical system includes a second optical system having an enlargement lens that forms an image on the screen, and the first optical system temporarily reduces the elongation rate, and the second optical system enlarges the image and projects it onto the screen. It is characterized by the following.

(Function) The image formed on the original image forms a reduced real image on the imaging plane by the lens applied with the reduction magnification of the first optical system by illuminating it, and this reduced image is used as the first image. The image is magnified by the magnifying lens of the two-optical system and projected obliquely onto the screen. In this case, the first optical system is placed on the imaging plane at an elongation rate of 1/
An image reduced to δ is formed and projected onto the screen by the second optical system at an elongation rate of δ, thereby making it possible to form an image without elongation.

(Example) The present invention will be described below with reference to the example shown in FIGS. 1 to 7.

FIG. 1 shows an embodiment of the oblique projection display device according to the present invention in a movable form, and FIG. 2 shows its longitudinal section.

In this embodiment, the box-shaped cabinet 1 has a thin depth D.
The cabinet 1 includes a projection optical system 2, a rear projection type screen 3 provided on the front surface of the cabinet 1, and a rear projection type screen 3 provided in the front surface of the cabinet 1. 1. It is provided with second reflecting mirrors 4 and 5.

The projection optical system 2 used in the present invention is shown in FIG.
) shows a transmission type optical system, and FIG. 3(B) shows an optical system of a reflective type. , an imaging surface 9, and a second optical system 10. The ride valve 7 uses a transmissive or reflective dot matrix liquid crystal.

The first optical system 8 has a lens 11 with a reduction magnification that focuses the image formed on the light valve 7 on the imaging surface 9 with a reduction magnification, and the second optical system 10 has a lens 11 that forms an image formed on the imaging surface 9 with a reduction magnification. It has a lens 12 with an enlarged magnification that forms an image on the screen 3 with an enlarged magnification.

The light valve 7 is installed at a predetermined angle with respect to the optical axis 13 of the first optical system 8, and the optical axis is located at a position where the image of the light valve 7 is formed by the reduction lens 11 of the first optical system 8. An image forming surface 9 is installed so as to be inclined toward the opposite side of the light valve 7 with respect to the light valve 13 .

In the case of a transmission type, as shown in FIG. 3(A), the magnifying lens of the second optical system 10, which has an optical axis 14 bent at the imaging plane 9 with respect to the optical axis 13 of the first optical system 8, is on the imaging plane. 9 is arranged between the reduction lens of the first optical system 8 and the second optical system 10.
The magnifying lens is arranged in a ``V'' shape. Through this second optical system 10, the image formed on the image forming surface 9 is enlarged and projected from an oblique direction onto the screen 3 which is inclined on the opposite side to the image forming surface 9. In addition, in the case of reflective type,
As shown in Fig. 3(B), the image forming surface 9 is connected to a reflecting mirror (Fig. 3(B)).
(C) is partially enlarged), and the second optical system 10 is disposed on the reflected optical path. The image forming surface 9 used in the transmission type is, for example, a minute reflective surface 15.15 that is long in the horizontal direction and narrow in the depth direction, as shown in a partially enlarged view in FIG.
The reflection means has a structure in which a large number of... are arranged in the vertical direction, and the light from the first optical system 8 is reflected by the minute reflection surface 15°15.
... and is formed so as to be reflected toward the lens of the first optical system 10. It is preferable to use such a reflecting means as the image forming surface because the loss of light is small, but if the area of the screen 3 is not very large (the magnification is small) or the amount of light from the illumination device 6 is large, the transmission may be difficult. A mold screen may also be used.

The screen 3 prevents the incident light flux from being transmitted in the extending direction from the back side of the screen 3 at an angle of incidence of 60°, as shown in a partially enlarged view in FIG. It is desirable to use a prismatic total reflection screen in which the front surface of the screen 3 is oriented almost at right angles.

Looking at the above-mentioned projection optical system 2 from a geometrical optical point of view, as shown in FIG. The extension line 15 of the light valve 7 and the extension line 17 of the imaging plane 9 intersect at the 0 point on a line 18 passing through the center of the lens 11 and perpendicular to the optical axis 13.

At this time, the magnification rate is m. is mo-f/(χ1-f)-(χ2-f)/f-χ2/χ
It is l. In other words, it is expressed as mo ''La1lα'2 / tan al (Scheinbruch's law).

By satisfying the above conditions, the image of the light valve 7 can be formed on the imaging plane 9 by the first optical system 8. However, as shown in FIG. 8, the image formed on the imaging plane 9 is an image distorted into a trapezoid if the original image is a regular square.

The second optical system 10 also arranges the image forming surface 9 and the screen 3 in the same relationship as the first optical system 8, so that the image on the image forming surface 9 is transferred to the second optical system 10. The image is enlarged and formed on the screen 3. This image shows the magnification of the lens 11 of the first optical system 8 and the magnification of the second optical system 10.
An image with a magnification multiplied by the magnification of the lens 12 is formed.

Here, in order to remove the trapezoidal distortion that occurs as described above, the first optical system 8 and the second optical system 1 of the projection optical system 2 are
This can be solved by adding the following conditions to the arrangement of each lens 11 and 12 of 0.

That is, as shown in FIG. 7(A), the front axis 1 of the lens 12 of the first optical system 8 at the focal position f1 on the image space side.
3 and the point c2 where the perpendicular to the lens 12 of the second optical system 10 intersects with the extension line 17 of the imaging surface 9, and the perpendicular to the optical axis 14 of the second optical system 10 at the focal position f2 on the object space side of the lens 12 and the imaging surface 9. It is configured such that the point C3 where it intersects with the extension line 17 coincides with the point C3.

In this case, as shown in FIG. 7(B), even if the optical axis 13 of the first optical system 8 and the optical axis 14 of the second optical system 10 are shifted on the image plane 9, the points C2 and 03 are aligned. As long as you have done so.

This is the case when the image forming surface 9 is a reflecting surface as shown in FIG. 3(C) as shown in FIG. 7(C), and an optical system is used to guide the reflected light flux from this reflecting surface to the screen 3. The same applies.

By satisfying the above conditions, a regular image without trapezoidal distortion could be obtained as an image on the screen 3 as shown in FIG. 9.

Below is the analysis result of the reason.

First, let us consider changes in the image of a square screen.

In FIG. 10, if the intersection between the focal plane and the object plane is 01, then the following equation is obtained.

The size of the object and image in the υ direction shown in FIGS. 10 and 11 is 'U1. 'tr2, the magnification rate m in the υ direction is
'U is m7j+- The size of the object and image in the U direction shown in Fig. 11. The magnification m in the U direction is It can be seen that the lines are of the same shape.

Next, looking at the straight lines u and -b, on the imaging plane side, g 2 - A 2 C2 - m ' Here, the trapezoidal distortion generated in the first optical system including the lens 8 is transferred to the second optical system. will be corrected. In this optical system, if 3 and 4 are added to the symbols and expressed by μ instead of the magnification m, it becomes μn μO u4″″ u3. Now, if the optical axis passes through A2 as shown in Figure 12, we have set the following. Note that there is no need to consider the direction since there is no asymmetry between the top and bottom.

The end result is generally a trapezoidal distortion type image, but g ””
If m' Ogl -g2, there will be no trapezoidal distortion.

In the present invention, the lens 11 of the first optical system 8 is a reducing lens, and the elongation rate therebetween is set to be canceled by the elongation rate due to the enlarging lens 12 of the second optical system 10.

If the elongation rate δ and the main magnification m are given, the angles α1 and α2 in Fig. 6 are determined, and the elongation rate σ does not exceed the main magnification mo, so the elongation rate δ is
>σ.

Therefore, in the first optical system 8, the elongation rate is set to 1/σ
By returning to , an image without trapezoidal distortion and stretch can be obtained on the screen 3.

The projection optical system 2 has an optical axis 13 of the first optical system 8 and a second optical axis.
Although the case where the optical axis 14 of the optical system 10 is arranged in a bent manner has been described, by satisfying the above-mentioned conditions, the optical axes 1, 3, and 14 can be arranged on the same axis as shown by the dotted line in FIG. By arranging the light valve 7 and the center of the screen 3 on their axes and maintaining the relationship α+α4=α4' in the figure, it is possible to obtain a projection optical system that exhibits the same effect as described above.

With this arrangement, the burden on the lenses 11 and 12 can be felt, and light can be used reasonably.

Referring to the embodiments shown in FIGS. 1 and 2, in this case, a projection optical system 2 is placed above the interior of the cabinet 1, and the light beam emitted from the projection optical system 2 is transmitted to the bottom of the cabinet 1 via a relay mirror 21. A second reflecting mirror 5 is placed on the rear inner surface opposite to the screen 3 and is parallel to the back surface of the screen 3. By projecting from the second reflection mirror 5 onto the back surface of the screen 3 from an oblique direction, the image formed on the light valve 7 is projected onto the screen 3 as an enlarged image.

Even if the above-mentioned arrangement structure is adopted and the screen is projected diagonally from the back side of the screen 3, the enlarged image formed on the screen 3 will not have trapezoidal distortion or elongation, and a normal image can be projected. However, the depth of the cabinet 1 can be greatly shortened, and an ultra-thin display device with a large screen can be obtained.

〔Effect of the invention〕

As explained above, according to the present invention, even if an oblique projection method is adopted for the projection optical system onto the screen, there is no trapezoidal distortion in the image on the screen, there is no elongation between the images, and the quality of the image on the screen is improved. can be significantly increased.

In addition, since there is no distortion or elongation of the image even when it is projected diagonally to the screen, when it is incorporated into a cabinet and used as a display type display device, it is possible to significantly reduce the volume of the cabinet, especially the depth. , a compact display device can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing one embodiment of the present invention, FIG. 2 is a vertical sectional view of the specific embodiment, and FIG. 3(A). (B) and (C) are explanatory diagrams of the projection optical system, FIG. 4 is an enlarged cross-sectional view of a part of the famous water showing an example of a reflection means when a reflection means is used on the image forming plane in FIG. 3, and FIG. The figure is an enlarged view of a part of an example of the screen, FIG. 6 is an explanatory diagram showing the relationship between the lens of the projection optical system, the light valve, and the imaging plane in FIG. A), (B),
(C) is a geometrical optical analysis diagram of the projection optical system according to the present invention, FIG. 8 is an explanatory diagram showing trapezoidal distortion of the imaging screen caused by the first optical system, and FIG. 9 is an image corrected by the second optical system. FIGS. 10 to 12 are explanatory diagrams showing that no trapezoidal distortion occurs, and FIG. 13 is an explanatory diagram of the oblique projection optical system. 1... Cabinet, 2... Projection optical system, 3...
Screen, 4... First reflecting mirror, 5... Second reflecting mirror, 6... Illumination device, 7... Light valve as original image, 8... First optical system, 9...・Imaging plane, 1
0...Second optical system.

Claims (1)

[Claims] 1. A first optical system having a lens with a reduction magnification that is arranged at a predetermined angle with respect to the surface of the original image that can transmit or reflect light and that reduces the original image and forms an image; It consists of an imaging plane placed at the imaging position of the first optical system, and a second optical system having a lens with an enlargement magnification that enlarges the reduced image formed on the imaging plane and forms the image on a screen. Equipped with a projection optical system,
1. An oblique projection display device characterized in that a first optical system temporarily reduces the elongation rate, and a second optical system enlarges and projects the image onto a screen. 2. The oblique projection display device according to claim 1, wherein the elongation rate σ_1 of the first optical system and the elongation rate σ_2 of the second optical system are set such that σ_1×σ_2≈1. 3. The oblique projection display device according to claim 1, wherein the optical axes of the first optical system and the second optical system are shifted so that a line connecting the original image, the imaging plane, and the screen becomes a substantially straight line. .