JPH03122607A - Projection lens for projector - Google Patents

Abstract

PURPOSE:To obtain a wide-angle, compact projection system and to compensate distortion, astigmatism, curvature of field, etc., excellently by arranging a tetrofocus type lens in a front lens group and an aspherical lens and a projection lens in a rear lens group. CONSTITUTION:The retrofocus lens part of the front group consists of a biconcave negative lens L1, a biconvex positive lens L2, a cemented lens L3+L4 composed of a biconcave negative lens L3 and a byconvex positive lens L4, a biconvex positive lens L5, and a negative meniscus lens L6 which has a concave surface on the side of a screen. The rear lens group consists of a negative plastic aspherical lens L7 which has a large-curvature concave surface at a periphery of the screen-side surface and also has negative power at the peripheral part and negative power at the paraxial part, and a biconvex positive lens L8. The composite paraxial power of the lenses L7 and L8 is positive and a stop is arranged between lenses L2 and L3. Consequently, the distortion can be compensated excellently and the astigmatism and curvature of field are compensated effectively; and the wide angle is obtained and the projection system is made compact.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a refractive projection lens for a projection system that projects an image on a liquid crystal display element onto a large screen.

[Conventional technology]

Conventionally, many projection television systems have been put into practical use, in which the screen of a projection tube (CRT) is projected onto a screen using a projection lens for a projector. In recent years, a type of projector in which an image on a liquid crystal display element is projected onto a screen using a projection lens for a projector has been put into practical use.

[Problem to be solved by the invention]

Unlike when projecting a CRT screen, there are the following problems when projecting a screen on a liquid crystal display element.

(2) In the case of a CRT, screen distortion can be electrically corrected, but in the case of a liquid crystal display element, it cannot be corrected. Therefore, it is desirable that the distortion aberration of a projection lens for a liquid crystal display element is within 1.2%.

■In order to project the image on the liquid crystal display element onto the screen evenly and with high contrast, it is necessary to use a beam of light that emerges from the liquid crystal display element at an angle close to perpendicular to the screen. Therefore, it is desirable that the principal ray of the projection lens forms an angle of 100 degrees or less with respect to the normal to the liquid crystal display element.

Furthermore, in order to make the entire projection system compact, it is necessary to widen the angle of the projection lens.

[Means to solve the problem]

In view of the current situation, the present invention consists of, in order from the screen side, a retrofocus type front group lens and a rear group lens consisting of an aspherical lens and a convex lens, and the power in the peripheral portion of the aspherical lens is negative. The projection lens for a projector is characterized in that the combined paraxial power of the rear group lens is positive.

[Effect]

In the present invention, by arranging an aspherical lens in the rear lens group, distortion is particularly well corrected, and astigmatism and field curvature are also effectively corrected.

In addition, by arranging a convex lens near the liquid crystal display element of the rear group lens, the principal ray of the projection lens is made almost parallel to the normal line of the liquid crystal display element, and the incidence of the projection lens as seen from the liquid crystal display element side is It is possible to move the eyes away.

Furthermore, by placing a retrofocus type lens in the front lens group, a wide angle of view has been achieved. As a result, the projection distance can be shortened, so that the projection system can be made more compact.

As for the retrofocus type lens of the front group lens, it is desirable that both lenses closest to the screen and closest to the liquid crystal display surface are negative lenses.

Aspherical surfaces work effectively in correcting distortion, and by using an aspherical surface with a strongly concave periphery on the screen side, the front group lens of the retrofocus type lens and the convex lens of the eighth lens L8 This overcorrects the image surface from being undersized, and effectively works to correct field curvature and astigmatism. In addition, especially distortion, which cannot be corrected with a retrofocus type front group lens,
For astigmatism and field curvature, it is desirable to arrange a plastic aspherical lens satisfying the condition of 0.05<DM/f<0.035 in the rear lens group.

However, DM: Thickness of the rear group aspherical lens at the effective diameter on the screen side f: Synthetic focal length of the entire system. Within the range of the above conditions, distortion, curvature of field, and astigmatism can be corrected even better.

In the present invention, the power in the peripheral part of the aspherical lens is negative, and the combined paraxial power of the rear group lens is positive, but the power in the paraxial part of the aspherical lens is positive,
It can be either negative.

As shown in Figure 3, it is also possible to widen the distance between the front group lens and the rear group lens and insert a mirror between them so that the projection optical system can be bent from the middle. The entire device including the system can be made more compact. Further, by making the surface of the eighth lens L8 close to the liquid crystal display element flat, it is possible to bond a polarizing plate to the surface.

〔Example〕

Embodiments of the present invention having the lens configurations shown in FIGS. 2 to 4 will be described below with reference to the drawings. The basic configuration is as follows. L is the third lens with negative power, L2 is the second lens with positive power, L is the third lens with negative power, L
4 is the fourth lens with positive power, the third lens L,
and the fourth lens L4 are cemented together. Ls is the fifth lens with positive power, L is the sixth lens with negative power, and the lenses L to LI1 constitute the retrofocus lens section of the front group. L7 is the 7th lens of a plastic aspherical lens whose periphery on the screen side forms a strongly concave surface and the power in the periphery is negative, and L is the 8th lens with positive power with a convex surface facing the screen side. The seventh lens L7 and the eighth lens L8 constitute a rear lens group.

The combined paraxial power of the seventh lens L7 and the eighth lens L is positive.

In the description of the numerical examples below, f: composite focal length of the projection lens θ: projection half angle of view FNO: F value β: projection magnification m Surface number rI counted sequentially from the second screen side First number counted from the second screen side Radius of curvature d of the second lens surface, Thickness or air gap nl of the i-th lens component counting from the second screen side, Refractive index for the d-line of the i-th lens component counting from the second screen side , Second screen side Atsube number of the i-th lens component counted from
When the direction perpendicular to the optical axis is the y-axis direction, +a, y'
It is expressed as +a2y'+a3y' +a4yIO.

However, C is the apex curvature, K is the eccentricity, and a1 to a4 are the aspheric coefficients.

Example 1 FIG. 1 shows Example 1.

The retrofocus lens section of the front group is a biconcave negative lens L.
1, a double-convex positive lens, 2, a double-concave negative lens L, and a cemented lens L of a double-convex positive lens L4, 10 L4, a double-convex positive lens L5, and a concave surface facing the screen side. It consists of a negative meniscus lens L6, and the rear group lens is a plastic aspherical lens whose periphery on the screen side forms a strongly concave surface, with negative power in the periphery and negative power in the paraxial part. It is composed of L7 and a biconvex positive lens LB. The combined paraxial power of lens L7 and lens L is positive.

A diaphragm is disposed between the lens L2 and the lens L.

f=58.48 θ=36.81°FNO=2.8
β=14.3m r d
n ν1 −645.120 3.00
1.500 52.32 35.230 8
．． 07 3 399.610 11.87 1.847
23.84 -136.640 28.545
-90.152 11.54 1.775
26.56 98.394 27.76 1
．． 609 62.67 -52.802 0.2
0 8 93.013 15.50 1.726
47.49 -171.231 14.70t
o -165,5003,201,84723,8
11-1557,73058,29 12* 206.400 5.00 1.
492 57.213* 231.670
2.0014 93.021 16.50
1.685 67.615 -320.
713 Aspheric coefficient 12th surface 13th surface a, 9.1372815 xlO-' 1.31
87810 xlO-'a2-2.0648674 X
10-'-1,6653955X 10-"a,
1.2814247 Xl0-”-8,47386
78Xl0-”a, -3,1409243XIO'
-1,5707755Xl0-''OD/f=0.31 Example 2 FIG. 2 shows a second example.

The retrofocus lens section of the front group is a biconcave negative lens L.
, a biconvex positive lens L2, a biconcave negative lens L, a cemented lens L of biconvex positive lenses 1 and 4, and a biconvex positive lens L5 and a biconcave negative lens L6. The rear group lens has a strong concave surface on the periphery of the surface on the screen side, and a plastic aspherical lens L7 with negative power on the periphery and positive power on the paraxial portion, and a plastic aspherical lens L7 on the screen side. It is composed of a positive meniscus lens L8 with a convex surface. The combined paraxial power of lens L7 and lens L8 is positive. A diaphragm is disposed between the lens L and the lens L.

f=59.810=36.79°FNo=2.8 β
=14.3m r d n
ν1 -378.800 3.00 1.4
99 50.22 32.450 8.88 3 232.340 13.06 1.847
23.84 -174.510 27.905
-86.294 1 (1991, 82423, 76
88,74123,891,66359,07-53,
0850,20 899,14613,391,84434,19-15
0,91022,22 10-101,9503,201,84723,8II
339.040 58.2612* -27
0,9005,001,49257,213* -1
56,230 1485,280 15436,060 Aspheric coefficient 12th surface a + -2,5638083X 10a, 8.94
17793 Xl0 1s 4.2131720 X 10 a48.8513201 XIO O I)+/f=0.06 Example 3 FIG. 3 shows Example 3.

The retrofocus lens section of the front group is a biconcave negative lens L.
1, a double-convex positive lens L2, a double-concave negative lens L, and a cemented lens L of a double-convex positive lens L4, +L, a double-convex positive lens L, and a double-concave negative lens L6. It consists of
The rear lens group forms a strongly concave surface on the periphery of the surface on the screen side, and the power on the periphery is negative 2.00 67.4 1, 500 13th surface 1, 8789914 x 10 1, 3306235 2,8374963 x 10 15.50, and is composed of a plastic aspherical lens L7 whose paraxial portion has a positive power and a 5-plane positive lens with its convex surface facing the screen side. The combined paraxial power of the lens L7 and the lens is positive. Lens L2 and lens L
, an aperture is arranged between the .

A reflecting mirror M is arranged between the front group retrofocus lens section and the rear group lens to bend the direction of light. This type allows the total length of the lens to be made compact by bending the total length of the optical path.

f=59.17 θ=36.74°FNO=2.8
β=14.3m r d n
ν1 −569.200 3.00
1.500 64.72 33.207 14
．． 98 3 934.930 17.59 1.847
23.84 -165.920 25.815
-102.860 12.79 1.829
30.56 95.997 25.89 1.5
91 63.87 -52.265 0.20 8 96.256 16.00 1.766
42.69 -142.600 11.9610
-125.210 11 1210.880! 2* 566.148 13* -867,990 1484,305 1500 Aspheric coefficient 12th surface a, 2.6597314 Xl0 a, -2,3364092Xl0 a! −1,893919i xlO a47.8342306 XIO O DM/f=0.16 FIGS. 5 to 7 are aberration curve diagrams corresponding to Examples 1 to 3, respectively. These figures were all drawn by defocusing from the Gaussian image plane to the lens side so that the central image is in the best condition. Each aberration diagram shows the wavelength e.
drawn with a line.

In the aberration curve diagrams of each of the first to third embodiments, 23.8 57.2 64.3 1.847 1.492 1, 549 13th surface 6.5941148 Xl0 -4.7465046 X 10 1, 4374523 X 10 3, 1013322

〔Effect of the invention〕

As is clear from the above description, according to the present invention, by arranging a retrofocus type lens in the front group lens and arranging an aspherical lens and a convex lens in the rear group lens,
In addition to widening the angle of view and making the projection system more compact, distortion, astigmatism, field curvature, etc. are well corrected, and
It has become possible to provide a projection lens for a projector that allows the chief ray to be made substantially parallel to the normal line of a liquid crystal display element.

[Brief explanation of drawings]

FIG. 1 is a lens configuration diagram of a first embodiment of a projection lens for a projector according to the present invention, FIG. 2 is a lens configuration diagram of a second embodiment, FIG. 3 is a lens configuration diagram of a third embodiment, and FIG. The figure is a schematic diagram of the main parts of an aspherical lens, Figure 5 is an aberration curve diagram of the first embodiment, Figure 6 is an aberration curve diagram of the second embodiment, and Figure 7 is an aberration curve diagram of the third embodiment. be. L8. . . . L,: 1st lens to 8th lens X: Optical axis rl, r2. ...r, 5: radius of curvature d of each lens surface
1, d2. ...d14: Thickness or air spacing of each lens S: Sagittal image surface t: Meridional image surface

Claims (1)

[Claims] It consists of, in order from the screen side, a retrofocus type front group lens and a rear group lens consisting of an aspherical lens and a convex lens, and the power in the peripheral part of the aspherical lens is negative, and the power of the rear group lens is negative. A projection lens for a projector characterized by positive paraxial power.