JPH0339916A - Projection lens - Google Patents

Abstract

PURPOSE:To obtain a large-aperture-ratio projection lens which has a >=30 deg. half visual angle and high optical performance by composing the projection lens of six elements in four groups and satisfying specific conditions. CONSTITUTION:The projection lens consists of a 1st group which has two aspherical surfaces which are convex to the screen side, a 2nd group consisting of two aspherical meniscus lenses which are concave to the screen side, and a 4th group consisting of a negative lens which has an aspherical concave surface on the screen side; and the 1st group consists of a lens 1a with negative refracting power and a lens 1b with positive refracting power, the curvature of the lens 1b is made larger than the curvature of the lens 1a, and conditions shown by expressions I are satisfied. In the expressions, (f) is the focal length of the whole lens system, f1 the focal length of the 1st group, d2 the air gap between the lenses 1a and 1b, and r3 the radius of curvature of the lens 1b on the screen side. Consequently, aberrations are compensated excellently over the entire image plane.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a wide-angle projection lens suitable for a video projector that enlarges and projects a CRT image onto a screen.

Prior art video projectors enlarge and project green, red and blue CRT images onto a screen using projection lenses. As a three-element projection lens, for example, Japanese Patent Application Laid-Open No. 55-124
114, JP-A-58-125007, JP-A-60-208720, etc. are known.

In addition, as a projection lens with a four-element configuration, JP-A-59-1
33517, JP-A-56-78815, JP-A-62-138811, etc. are known. Furthermore, as a five-element projection lens,
Publication No. 5611 and the like are known.

Recently, efforts have been made to reduce the depth of video projector sets, and as a countermeasure to this, there is a strong demand for a projection lens that can realize a wider angle of view than conventional projection lenses.

Problem to be solved by the invention In order to shorten the depth of the video projector, the half angle of view is 30 mm.
'A projection lens with a capacity of A projection lens designed to achieve such a wide angle of view suffers from deterioration in resolution and a decrease in the amount of peripheral light at large angles of view.

The present invention solves the above problems and provides a projection lens with a large aperture ratio of 1° or less and a wide angle of view with a half angle of view of 30° or more.

Means for Solving the Problems In order to solve the above problems, the projection lens of the present invention has the following features:
From the screen side, 2 with the convex side facing the screen side.
a first group consisting of a meniscus lens having aspherical surfaces;
A second group consisting of two biconvex positive lenses, a third group consisting of a meniscus lens with an aspherical surface facing the screen side, and a fourth group consisting of a negative lens having an aspherical concave surface facing the screen side. The first group consists of a 1a lens with negative refractive power and a 1b lens with positive refractive power, and the curvature of the 1b lens is larger than the curvature of the 1a lens, and the following conditions are satisfied: The configuration is such that the

−0,1≦f/f,≦0.2 ・・・・・・(1)
0≦d, /f≦0.03 (2) 0.
3≦ry/r≦1.0 (3)
However, f: Focal length of the entire lens system rl: Focal length of the first group d2: Air distance between the 1a lens and the 1b lens γff: Radius of curvature of the 1b lens on the screen side Furthermore, high performance with a wide angle of view In order to realize a projection lens that is
The focal length of the third group is f, the air distance between the second and third groups is ds, and the air distance between the third and fourth groups is d10.
When doing so, it is desirable to satisfy the following conditions.

=o, i ≦f; /f, ≦0.3 ・・・・・・(
4) 0.6≦da/dlo≦1.5 (
5) Function The projection lens of the present invention is configured with 6 elements in 4 groups as described above, and by providing the above conditions, it is possible to realize a large aperture ratio projection lens having high optical performance at a half angle of view of 30' or more. made possible.

First, a so-called Gaussian objective lens consisting of a first group, a meniscus 1a lens with negative refractive power, and a meniscus 1b lens with positive refractive power is constructed by modifying it.
This makes it possible to correct spherical aberrations and off-axis aberrations.

Condition (1) gives the relationship between the focal length of the first group and the focal length of the entire lens system; if the upper limit is exceeded, it becomes difficult to correct off-axis aberrations, especially sagittal coma aberration; if the lower limit is exceeded, It becomes difficult to correct spherical aberration.

Condition (2) gives the positional relationship between the 1a lens and the 1b lens, and if the upper limit is exceeded, it becomes difficult to correct comatic aberration and spherical aberration.

When the upper limit of condition (3) is exceeded, it becomes difficult to correct off-axis comatic aberration, and when the lower limit is exceeded, it becomes difficult to correct spherical aberration.

Condition (4) gives the relationship between the focal length of the third group and the focal length of the entire lens system; if the upper limit is exceeded, the correction of the field curvature will be insufficient, and if the lower limit is exceeded, the correction of the field curvature will be excessive. Become.

Condition (5) gives the positional relationship of the third group with respect to the second and fourth groups.If the limit is exceeded, it becomes difficult to correct spherical aberration, and if the lower limit is exceeded, it is difficult to correct the curvature of field. become.

EXAMPLE Hereinafter, a projection lens according to an example of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of the projection lens of the present invention. In FIG. 1, 01 is a first group consisting of two aspherical meniscus lenses Ll and L2 with the convex surface facing the screen side, G2 is a second group consisting of two biconvex positive lenses L3 and L4, G3 is a meniscus lens with an aspherical surface facing the screen side L5
G4 is the fourth group consisting of a negative lens L6 with an aspherical concave surface facing the screen, and the lens L1 of the first group G has a negative refractive power, and L2 has a positive refractive power. .

Note that the curvature of the lens L2 is steeper than that of the lens Ll. P is the CRT face plate, C is lens L6 and C
It is an optically transparent medium that fills the gap between the face plate 1-P of the RT and the bottom of the tank is filled with ethylene glycol, silicone gel, or the like.

Hereinafter, specific examples 1 and 2 of the present invention will be shown. In the tables of these examples, f is the focal length of the entire lens system, FN
O is the F number, ω is the half angle of view, β is the projection magnification, fl
is the focal length of the 1a lens L1, and fh is the 1b lens L1.
Focal length of 2, f.

is the focal length of the first group Gl, and f is the focal length of the third group G3. In addition, γ1, Tt... are the radius of curvature of each lens surface counted sequentially from the screen side, dl, G2...
... is the center thickness and air spacing of each lens, nl, n2
...... is the refractive index of each lens relative to eta, ν5
, ν2... indicate the Atsube number of each lens. Furthermore, the lens surfaces marked with * indicate aspherical surfaces, and the aspherical shape of the projection lens according to the present invention has an optical axis direction of X,
The Y axis is perpendicular to the X axis, and the apex curvature is C (=l/r),
When the conic constant is K and the aspherical coefficients are AD, AE, AF, and AC, it is expressed by the following equation.

(Example 1) f = 88.4 (1) Seagull FNO = 1.1 β = -
8, 1f, = -1019mm ft = 9080am h = -2720mm ω = 33.
8' fb=867mm Aspheric coefficient first surface (r,) K=-9,41035 AD= 1.36460xlO-" AE=-3,94452X 10-" AP= 5.
80464x10-0 2nd surface (r2) K=O AD= 4.93621X10-'^E=-3.63720X10-'"AP=-1,73931X10-1"AG=-1,76921XlO-" 3rd surface ( ",) に=-4,15517X10-'AD=-2,91889X10-' AE= 1,05648X10-0 AF= 5.23660X10-" AG= 2.8B252X10-7 9th surface (r,) K=O 〇 = 2.82983X10-' AE = 5.99327X10-'' AP = 2.53529xlO-I3AG = -2,1
3,236 (Example 2) AG= 5.13722xlO-” 4th surface (r4)=-4,0?246X10-'AD=-1,86555X10-' AE= 1.24229X10-" AP= 1.78690XIO-" AG= 2.82872XlO-17 10th surface (“1
゜) K=O to 〇= 4.40009X10-' AE= 6.0770 Xl0-108F --2
,39904X 10-”AG=-6,52225X
10-” f =79.7mm FNO=1.1 36.6' β--8,1 f, = 83mm b 760a+m f l= -2007n+m f3=2136mm Aspheric coefficient 1st surface (r+) 2nd surface Crt ) K-4, 25460X10 AD= 2.72743X10"" AE=-6,38993XIO- AF= 1゜45162X10-" AG =-6,07628X 10-" 3rd surface (r,
) K = -3,82195X10-' To = -4.51035X10-' 8E = 1.653745
1.10675X10-' AF= 7.45888XlO-'' 9th surface (r,) K=0 to D= 1.25576X10-' AE= 9.66885X10-' AF= 5.27140xlO-13AG=-5,3
7833XIO-" 11th side (r,) K-~1.08046X10""AD=-7,52744X10-" K=O AD= 6.99597xlO-' ΔB= 7.13712X10-" AF=-3,67508X10 To G= 1.17703XIO”” To the 4th side (r4)=-3,79519XIO-' To --2,76486X 10-'AE= 2
．． 22759X10 Aσ=3゜69351
゜) K=-O AD= 1゜2B286x10-7 AE= 1.07052X10-9 8F-~4.41779 X 10” ”AG=-2,
09184XIO AE-9,96589xlO-'AF=-5.95147X10-" AG= 1.54900X10-" FIGS. 2(a) and 2(b) show various aberration diagrams of Example 1, and the third
Figures (a) and (b) show various aberration diagrams of Example 2. m indicates the curvature of field in the meridional direction, and S indicates the curvature of field in the sagittal direction.As is clear from the various aberration diagrams above, the wide-angle projection lens of the present invention has well corrected aberrations.
It has bright and high-contrast imaging performance.

Effects of the Invention As described above, by satisfying the lens, lens configuration, and various conditions of the present invention, it is possible to realize a wide-angle projection lens for a video projector that can perform good aberration correction on all sides. .

[Brief explanation of drawings]

FIG. 1 is a block diagram of a projection lens according to an embodiment of the present invention, and FIGS. 2 and 3 are diagrams of various aberrations for the embodiment of the present invention. G1...First group, G2...Second group, G
3...3rd group, G4...4th group, C.
...Optical transparent medium, P...CRT face plate.

Claims (1)

[Scope of Claims] (1) Used in a television image projection display device, in order from the screen side, a first group consisting of a meniscus lens having two aspherical surfaces with convex surfaces facing the screen side;
The second group consists of a double-convex positive lens, the third group consists of a meniscus lens with an aspherical surface facing the screen, and the fourth group consists of a negative lens with an aspherical concave surface facing the screen. The first group consists of a 1a lens with a negative refractive power and a 1b lens with a positive refractive power, and the curvature of the 1b lens is larger than the curvature of the 1a lens, and the following conditions are satisfied: A projection lens characterized by: -0.1≦f/f_1≦0.2 0≦d_2/f≦0.03 0.3≦r_3/f≦1.0 Where, f: Focal length of the entire lens system f_1: Focal length of the first group d_2: Air distance between the 1a lens and the 1b lens r_3: Radius of curvature of the 1b lens on the screen side (2) When the focal length of the 3rd group is f_3, the following conditions are satisfied. The projection lens according to claim (1). -0.1≦f/f_3≦0.3 (3) The air gap between the second group and the third group is d_8, and the third
2. The projection lens according to claim 1, wherein the projection lens satisfies the following condition when the air distance between the group and the fourth group is d_1_0. 0.6≦d_8/d_1_0≦1.5