JP2989947B2 - Optical system for projection display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system for a projection display apparatus for obtaining a thin and large image.

[0002]

2. Description of the Related Art A rear projection display device is known as a display device for enlarging and displaying an image using a display device such as a liquid crystal display panel or a cathode ray tube. For example, when looking at a device that obtains a screen of about 40 inches, as a first method, in the case of a direct-view tube television using a CRT as shown in FIG. 1, the size of the CRT itself almost determines the size of the device. The depth is over 70cm.

[0003] As a second system, even when a system is used in which a small CRT of about 7 "as shown in Fig. 2 is used for projection, the CRT and the projection lens are large, and the apparatus is so much compared with the system of Fig. 1 described above. Although not made thinner, it is currently used for large-screen displays whose cathode ray tube production capacity exceeds 40 "out of a maximum of about 40" in terms of cost.

In the system shown in FIG. 2, if a small and thin liquid crystal display panel of about 3 ″ is used instead of a small cathode ray tube, the size and weight can be reduced as shown in FIG. On the other hand, in order to further reduce the thickness of the device, it has been conventionally considered to arrange the projection lens obliquely to the screen as shown in FIG. However, this arrangement can reduce the thickness, but in this optical system, the image projected on the screen becomes a trapezoidally distorted image as shown in FIG. This is because there is a difference in the projection magnification of each point. As a countermeasure, trapezoidal distortion can be canceled on the screen by making the liquid crystal display panel etc. have an inverted trapezoidal shape. But manufacturing, not intended be realistic when viewed from the cost.

As means for correcting the trapezoidal distortion, for example, JP-A-1-257834 and JP-A-2-79037
There are those described in Japanese Patent Application Publication No. H10-26095. FIG. 6 is disclosed in Japanese Patent Application Laid-Open No. 1-257834, and FIG.
BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram of the Example disclosed by each 9037 publication. Japanese Patent Application Laid-Open No. 1-257834 discloses that a reflecting mirror is formed into a shape having an optical action equivalent to that of a rotationally asymmetric aspherical mirror as shown in FIG. 6 to correct trapezoidal distortion and achieve a thinner device. Since the mirror is large, complicated, and a mirror, high accuracy is required, the cost is very high, and trapezoidal distortion correction is limited. Also, as shown in FIG. 7, the above-mentioned Japanese Patent Application Laid-Open No. 2-78037 discloses an image (=
It has been proposed that an image having a trapezoidal distortion) be provided with another one-stage optical system, and an inverse trapezoidal distortion is generated by this optical system to form an image without distortion on a screen. But,
In order to reduce the thickness of the device, a display panel, a first lens,
The second lens and the screen must be tilted relatively large. The relationship of the inclination for correcting the trapezoidal distortion is as described in the above-mentioned publication. However, when the first lens and the second lens are relatively largely inclined, the light transmitted through the first lens is relayed to the second lens. The problem that is not done occurs. For this reason, the effective diameter of the second lens must be considerably increased. Also, in a normal optical system in which the object plane and the image plane are perpendicular to the optical axis without tilt eccentricity and parallel eccentricity, rays reaching the same image height from the optical axis are naturally optical axis symmetric in the lens system. When the lens has a tilted eccentricity or a parallel eccentricity, if the lens has a tilted eccentricity or a parallel eccentricity, the ray from the reference optical axis to the image height of the same distance from the reference optical axis in the decentered meridional section As is clear from the situation of the light rays in FIG. 7, it is difficult to relay the above-mentioned light rays, and at the same time, the incident position and the incident angle of the light rays are greatly different in each lens. Even if the paraxial and geometrical imaging relations are established by calculation, in such a case, an aberration surface, particularly distortion and astigmatism, are very large, and the amount of curvature of the image surface is greatly different. etc,
There is a problem that the level is not negligible as a display device. There is no conventional example that proposes an optical system that corrects the above-described aberration in an eccentric optical system that performs oblique projection with such a lens tilted.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a device for enlarging a display image on a display body by a projection lens and projecting the image on a screen, in order to reduce the depth to about half the depth of vertical projection. An optical system for a projection display device that can correct not only the trapezoidal distortion of an image caused by tilting and eccentricity of a lens but also various aberrations and obtain good image performance in an optical system that performs 60 ° incidence. The purpose is to provide.

[0007]

In order to achieve the above object, the present invention provides a screen having a positive refracting power as shown in FIG. 8 with respect to a screen which is inclined by 60 ° from a state perpendicular to the reference optical axis. With the above five lens groups, paraxial trapezoidal distortion correction division is performed, and the amount of eccentricity of each lens is
The amount of tilt eccentricity from the reference optical axis is Δθn, and the amount of parallel eccentricity is ΔS
When n is set, Δθn and ΔSn may be arranged so as to satisfy | Δθn | <10 ° | ΔSn | <7.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical system for a projection display according to the present invention will be described below. FIG. 8 shows the paraxial principle of the optical system according to the present invention.
To form an intermediate image I having trapezoidal distortion, and this intermediate image I further forms an intermediate image II having trapezoidal distortion in the same direction by the lenses 3 and 4. And this intermediate image II
Is imaged on the screen S by the lens 5 with the trapezoidal distortion cancelled. The first-stage lens group of the lens 1 and the lens 2 and the second-stage lens group of the lens 3 and the lens 4 have a configuration close to telecentric on both sides.
Has a configuration close to telecentric similarly, so that light beam matching is improved despite the decentered optical system. 9A and 9B are a lens sectional view and an optical path diagram of a numerical example of the present invention. Paraxially,
An imaging relationship in which trapezoidal distortion is corrected can be calculated. Generally, as shown in FIG. 9 (A), a plurality of lenses which are eccentric with respect to the reference optical axis and which are symmetric with respect to the reference optical axis on the display body surface. If ray tracing is performed with a real ray for the image height of the image, an image should be formed at a position symmetrical to the reference optical axis on the screen, but this is greatly distorted. This is due to the fact that the incident position and incident angle of each lens are different for the upper and lower rays because the lenses are decentered,
This is because the amount of generation of distortion greatly differs. In an eccentric optical system, it is important to correct distortions above and below the reference optical axis in a plane including eccentricity more than the inclination of the object plane and the image plane with respect to the lens for correcting trapezoidal distortion. If a rotationally asymmetrical aspherical lens is used instead of a spherical lens for this correction, it is easy to guess that the correction is possible, but it is not realistic in terms of processing and cost.

In order to correct various aberrations including this distortion, in general correction means such as bending of curvature, change of thickness, interval, and change of glass material, the optical system is rotationally asymmetric. It is difficult to make corrections in a well-balanced manner, and corrections can be made by appropriately giving the amount of tilt eccentricity and parallel eccentricity of the lens. However, assuming that the amount of tilt eccentricity of each lens is Δθn and the amount of parallel eccentricity is ΔSn, if | Δθn | <10 ° | ΔSn | <7 is not satisfied, distortion and other aberrations generated by the decentered optical system may be reduced. It is difficult to satisfactorily correct.
At the same time, matching of light rays between the lenses deteriorates, and a sufficient light amount cannot be secured.

Next, numerical examples of the present invention will be described. Numerical γi In embodiments the radius of curvature of the i-th lens surface in order from the screen side, d _i is the i-th eccentricity front of the lens thickness or air spacing in order from the screen side, n _i and [nu _i than each screen side The refractive index and the Abbe number at the d-line of the ith lens in order. Δθi and ΔSi are values decentered for each block or single lens based on the ith surface in order from the screen side. 9A, the tilt eccentricity .DELTA..theta.i is positive for counterclockwise rotation and negative for clockwise rotation, and the parallel eccentricity .DELTA.Si is positive for upward shift and downward for the reference optical axis. Shift is negative. The lens enclosed in parentheses is eccentrically integrated with the block.

In this embodiment, a 3 "liquid crystal display panel is assumed as a display body, the screen size is 50" diagonal, and the projection distance from the front surface of the lens to the screen is 35.
45mm, display body tilt 8 °, screen tilt 6
0 °. Further, in the present embodiment, FIG. 9B is rotated by 90 ° about the reference optical axis with respect to the direction of FIG.
In order to correct the magnification to 1: 1 in the vertical and horizontal directions, the lens has a refractive power in the direction of FIG. 9B in front of the fifth lens unit on the screen side. An anamorphic lens system for the data may be inserted. In the reference example of the anamorphic lens, Ari is the radius of curvature of the i-th cylindrical lens surface in order from the screen side, A
di is the thickness of the i-th cylindrical lens and the air gap in order from the screen side, and Ani and Aνi are the refractive index and the Abpe number of the i-th cylindrical lens in the d-line from the screen side, respectively.

[0012]

(Equation 1)

[0013]

(Equation 2)

[0014]

As described above, in the optical system for a projection type display device according to the present invention, the optical system is divided into five groups, and the amount of eccentricity of the lens eccentricity and parallel eccentricity is specified. , Achieved an optical system of 30 ° incidence on the screen, was thin and maintained the image performance,
An optical system for a projection display device can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a conventional projection display device.

FIG. 2 is a cross-sectional view of a conventional projection display device.

FIG. 3 is a cross-sectional view of a conventional projection display device.

FIG. 4 is a cross-sectional view of a conventional oblique projection type projection display device;

FIG. 5 is a diagram showing an image forming relationship between a display body and a projected image in an oblique projection system.

FIG. 6 shows a conventional example in which trapezoidal distortion is corrected in the oblique projection method,

FIG. 7 shows a conventional example in which trapezoidal distortion is corrected in the oblique projection method,

FIG. 8 is a diagram showing a basic optical system of the present embodiment;

9A and 9B are a configuration diagram and an optical path diagram of the present embodiment,

FIG. 10 is an explanatory diagram showing spot performance and distortion when an anamorphic lens is mounted, and is an evaluation on a screen. The spot is magnified 5 times with respect to the screen. The spot is indicated by 100 light rays at one place.

[Explanation of symbols]

 Reference Signs List 1 lens 2 lens 3 lens 4 lens 5 lens P display S screen I intermediate image II intermediate image

Claims (3)

(57) [Claims] 1. A projection display device in which an original image of a display such as a liquid crystal display panel is enlarged by a projection lens and projected on a screen, wherein the projection lens comprises five lens groups having a positive refractive power. Is eccentric with respect to a reference optical axis. 2. The optical system according to claim 1, wherein the screen is inclined by 60 ° from a state perpendicular to the reference optical axis. 3. The lens group according to claim 1, wherein Δθn is the amount of tilt eccentricity from the reference optical axis and ΔSn is the amount of parallel eccentricity from the reference optical axis.
3. The optical system for a projection display device according to claim 1, wherein ΔSn and | Δθn | <10 ° | ΔSn | <7.