JPH05119283A - Optical system for projection type display device - Google Patents

Abstract

PURPOSE:To obtain excellent image performance when a display image on a display device is enlarged by a projection lens and projected on a screen by composing the projection lens of five lens groups which have positive refracting power and making it eccentric with a reference optical axis. CONSTITUTION:In the optical system which makes light incident on the screen at 60, the lenses are made eccentric slantingly and in parallel. The original image on the display body P forms an intermediate image I with trapezoid distortion and the intermediate image I, further, forms an intermediate image II having trapezoid distortion in the same direction through lenses 3 and 4. Then the intermediate image II is formed on the screen S through a lens 5 as an image having its trapezoid distortion canceled. The lens groups of the 1st stages of the lenses 1 and 2 and the lens groups of the 2nd stages of the lenses 3 and 4 have almost telecentric constitution on both sides and the lens 5 has almost telecentric constitution as well, so light beams are excellently matched in spite of the eccentric optical system.

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 type display device for obtaining a thin and large image.

[0002]

2. Description of the Related Art A rear projection type 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 TV using a CRT as shown in FIG. 1, the size of the CRT itself determines the size of the device. The depth is over 70 cm.

As a second method, even if the projection is carried out by using a small cathode ray tube of about 7 ″ as shown in FIG. 2, the cathode ray tube and the projection lens are large, and the apparatus is so much compared with the method of FIG. Although it is not possible to make it thinner, the cathode ray tube is currently used for a large-screen display whose production capacity exceeds 40 "out of the maximum of 40" in terms of cost.

In the system of FIG. 2, if a small and thin liquid crystal display panel of about 3 ″ is used instead of the small cathode ray tube, the size and weight can be reduced as shown in FIG. However, in order to further reduce the thickness of the device, it has been conventionally considered that the projection lens is diagonally opposed to the screen as shown in FIG. However, although it is possible to reduce the thickness by arranging in this way, the problem that the image projected on the screen becomes a trapezoidal distorted image as shown in FIG. This is because there is a difference in the projection magnification of each point, and as a countermeasure, if the LCD panel etc. has an inverted trapezoidal shape, it is possible to cancel the trapezoidal distortion on the screen. But manufacturing, not intended be realistic when viewed from the cost.

Means for correcting this trapezoidal distortion are disclosed, for example, in Japanese Patent Laid-Open Nos. 1-257834 and 2-79037.
There is one as described in Japanese Patent Publication. FIG. 6 is the above-mentioned JP-A-1-257834, and FIG. 7 is the above-mentioned JP-A-2-7.
It is a block diagram of the Example each disclosed by the 9037 publication. In Japanese Patent Laid-Open No. 1-257834 mentioned above, 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 to achieve a thin device. Since the mirror is large and complicated and it is a mirror, high accuracy is required, and the cost becomes very expensive, and there is a limit in trapezoidal distortion correction. Further, in Japanese Patent Laid-Open No. 2-78037, as shown in FIG. 7, an image of a display panel (=
It has been proposed that another stage optical system should be provided for an image having a trapezoidal distortion), and an inverse trapezoidal distortion should be generated by this optical system to form an image without distortion on the screen. But,
In order to make the device thinner, the display panel, the 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 publication, but the light rays transmitted through the first lens are relayed to the second lens due to the relatively large inclination of the first lens and the second lens. There is a problem that is not done. For this reason, the effective diameter of the second lens must be made considerably large. Also, in an ordinary optical system in which the object plane and the image plane are perpendicular to the optical axis without tilt decentering or parallel decentering, the light rays reaching the image height of the same distance from the optical axis are naturally symmetric about the optical axis in the lens system. However, if the lens has tilt decentering or parallel decentering, the ray from the reference optical axis to the image height of the same sharpness in the decentered meridional section will pass. As is clear from the situation of 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 largely different in each lens. Even if the paraxial and geometrical imaging relations are established by calculation, in such a case, an aberration surface, especially distortion and astigmatism are very large, and the amount of curvature of the image plane is greatly different. etc,
There was a problem that it was not at a level that could be ignored as a display device. In addition, there is no conventional example that proposes an optical system in which the above-described aberration is corrected by a decentered optical system that performs oblique projection with such a lens tilt.

[0006]

It is an object of the present invention to provide a device for enlarging a display image of a display body by a projection lens and projecting it on a screen in order to reduce the depth of the screen by about half of the vertical projection. An optical system for a projection display device capable of correcting various aberrations as well as trapezoidal distortion of an image generated by tilting and decentering a lens in an optical system performing 60 ° incidence and obtaining good image performance. For the purpose of providing.

[0007]

In order to achieve the above object, the present invention has a positive refracting power as shown in FIG. 8 for a screen inclined by 60 ° from the state perpendicular to the reference optical axis. By configuring with five lens groups, paraxial trapezoidal distortion correction division is performed, and the eccentricity of each lens is
The tilt eccentricity from the reference optical axis is Δθn, and the 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 device of the present invention will be described below. FIG. 8 shows the paraxial principle of the optical system of the present invention. The original image of the display P is the lens 1 and the lens 2.
To form an intermediate image I having a trapezoidal distortion, and this intermediate image I further forms an intermediate image II having a trapezoidal distortion in the same direction by the lenses 3 and 4. And this intermediate image II
An image in which the trapezoidal distortion is canceled is formed on the screen S by the lens 5. The first-stage lens group of the lenses 1 and 2 and the second-stage lens group of the lenses 3 and 4 have a structure in which both sides are close to telecentric.
Also has a configuration close to that of telecentricity, so that the matching of rays is improved despite the decentered optical system. 9A and 9B are a lens cross-sectional view and an optical path diagram of a numerical example of the present invention. Paraxially,
It is possible to calculate the image formation relationship in which the trapezoidal distortion is corrected, but in general, a lens as shown in FIG. 9A is a plane decentered with respect to the reference optical axis, and a plurality of lenses symmetrical to the reference optical axis on the display surface. If ray tracing is performed with an actual ray for the image height of, the image should be formed at a position symmetrical with the reference optical axis on the screen, but the image is greatly distorted. This is because the incident position and incident angle of each lens are different in the upper and lower light rays because the lens is decentered.
This is because the amount of distortion aberration also greatly differs. In the decentering optical system, it is important to correct the distortion aberration above and below the reference optical axis in the plane including decentering beyond the tilt relationship between the object plane and the image plane for correcting the trapezoidal distortion. It is easy to estimate that if a rotationally asymmetric aspherical lens is used instead of a spherical lens for this correction, it is possible to make the correction, but this is not practical in terms of processing and cost.

In order to correct various aberrations including the distortion aberration, in the general correction means such as bending of curvature, change of thickness and interval, and correction of aberration by changing glass material, the optical system is rotationally asymmetrical. It is difficult to correct in a well-balanced manner, and correction can be performed by appropriately providing the tilt eccentricity and parallel eccentricity of the lens. However, assuming that the tilt decentering amount of each lens is Δθn and the parallel decentering amount is ΔSn, if | Δθn | <10 ° | ΔSn | <7 is not satisfied, distortion and other aberrations generated by the decentering optical system It becomes difficult to correct it well.
At the same time, the matching of light rays between the lenses is deteriorated, and a sufficient amount of light cannot be secured.

Next, numerical examples of the present invention will be shown. In the numerical examples, γ _i is the radius of curvature of the i-th lens surface in order from the screen side, d _i is the i-th pre-eccentric lens thickness and air gap in order from the screen side, and n _i and ν _i are from the screen side, respectively. The refractive index and the Abbe number at the d-line of the i-th lens are in order. Δθi and ΔSi are values decentered for each block or single lens with reference to the i-th surface in order from the screen side. 9A, the tilt eccentricity amount Δθi is positive in the counterclockwise rotation and negative in the clockwise rotation, and the parallel eccentricity amount ΔSi is positive in the upward shift and downward in the reference optical axis. The shift of is negative. The lens surrounded by parentheses is eccentric with the block as a unit.

In this embodiment, it is assumed that the display body is a 3 "liquid crystal display panel, the screen size is a diagonal length of 50", and the projection distance from the lens front surface to the screen is 35.
45mm, display surface tilt 8 °, screen tilt 6
It is 0 °. In addition, in the present embodiment, FIG. 9B is obtained by rotating the reference optical axis by 90 ° with respect to the direction of FIG. 9A.
The magnification ratio in the direction of is 1/2, and in order to correct the magnification ratio to 1: 1 in the vertical and horizontal directions, there is 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 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, Ari
di is the i-th cylindrical lens thickness and air distance from the screen side in order, and Ani and Aνi are the d-line refractive index and the Abbe number of the i-th cylindrical lens from the screen side, respectively.

[0012]

[Equation 1]

[0013]

[Equation 2]

[0014]

As described above, in the optical system for a projection display apparatus according to the present invention, the optical system is divided into five groups, and the tilt eccentricity of the lens and the eccentricity of the parallel eccentricity are specified. Achieves an optical system with an incident angle of 30 ° to the screen, which is thin and maintains image performance.
An optical system for a projection display device can be provided.

[Brief description of 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 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 the oblique projection method,

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

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

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

9A and 9B are configuration diagrams and optical path diagrams of this embodiment,

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

[Explanation of symbols]

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

Claims (3)

[Claims] 1. In a projection display device for enlarging an original image of a display body such as a liquid crystal display panel by a projection lens and projecting it on a screen, the projection lens is composed of five lens groups each having a positive refractive power. The optical system for a projection display device is characterized in that is decentered with respect to the reference optical axis. 2. The optical system for a projection display device according to claim 1, wherein the screen is inclined by 60 ° from a state perpendicular to the reference optical axis. 3. The lens group, wherein Δθn is a tilt eccentricity from a reference optical axis and ΔSn is a parallel eccentricity.
And ΔSn is | Δθn | <10 ° | ΔSn | <7. The optical system for a projection display apparatus according to claim 1 or 2, wherein