JPS6167813A - Projection lens - Google Patents

Abstract

PURPOSE:To obtain a projection lens having a large aperture, a wide picture angle and superior picture quality by arranging a meniscus lens having positive refractive index, a both-convex shaped lens and a convex lens having a large curvature successively and setting up the radiuses of curvature and intervals between surfaces on an optical axis so that specific formulas are satisfied. CONSTITUTION:The positive meniscus lens L1, the both-convex type lens L2 and the concave lens L3 having a large curvature which are made of plastic lenses are arranged successively from the screen side. Specific conditional formulas are set up between the radiuses R of curvature of respective lens surfaces and surface intervals D on the axis. The formula (1) is used for the compensation of corona aberration and spherical aberration, the formulas (3), (4) are used for the compensation of spherical aberration, out-axis aberration and comma aberration and the formula (5) is used for the compensation of an image surface curve and the formula (9) compensates the spherical and out-axis aberrations. In addition, the formula (6) is used for the cost reduction and the improvement of accuracy, the formula (7) expands the picture angle of the lens and the formulas (6) is used for the cost reduction and the improvement of accuracy, the formula (7) expands the picture angle of the lens and the formulas (1)-(4), (6), (9) suppress the increase of lens power. Consequently, the projection lens having a large aperture, a wide picture angle and superior picture quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a projection lens, and in particular to an enlarged projection lens suitable for enlarging and projecting an image projected on an electronic picture tube onto a screen and capable of realizing a large screen. Regarding.

In general, a projection lens for displaying images uses monochromatic cathode ray tubes in three colors of red, blue, and green for displaying color images, and each image is projected onto a screen by the projection lens.
Since both the color development characteristics and the spectral width are relatively narrow, it is not necessary to use an achromatic lens.

The desired conditions for a projection lens are a large aperture and a wide angle of view. The large aperture makes it possible to obtain a bright image, and the wide angle of view makes it possible to obtain a desired projected image at a short projection distance, making it possible to downsize the entire device.

Conventional projection lenses include spherical lenses with only spherical surfaces and aspheric lenses that include aspherical surfaces, but it is extremely difficult to reduce aI and the number of lenses and improve performance with a single spherical lens, so aspherical lenses have been introduced in recent years. Aspheric lenses are the mainstream.

However, the history of the projection lens itself in which aberrations are corrected using an aspheric surface is long, and British Patent No. 593,514 is known. The projection lens disclosed in this patent is a composite lens consisting of a biconvex lens and a biconcave lens in order from the image plane side.
2, which has an aspherical surface and has a convex surface facing the IL screen side, which corrects aberrations that mainly depend on the aperture and axial chromatic aberration.
It consists of a positive second group consisting of two plano-convex lenses, and a third n-th group having negative refractive power for image plane flattening means, all of which are made of plastic lenses. However, with this configuration, among the aberrations of spherical aberration, curvature of field, and coma, the first group lens causes spherical aberration, coma aberration, and @3
Although field curvature and distortion are corrected by the first group, the correction of spherical aberration and coma aberration corrected by the first group is insufficient, and the correction of coma aberration is particularly poor. This results in a flare that impairs the imaging performance, making it difficult to provide a projection lens with a wide field angle of 25 degrees or more.

(Objective) An object of the present invention is to provide a projection lens with a large diameter, a wide angle of view, and excellent image quality.

The example described later has an aperture ratio of 1:1.2 and a half angle of view of 251.
It has achieved a large aperture and wide angle of view of over 200mm.

In order to realize the purpose mentioned above, FIGS.

The projection lens shown in Figure 3 has a first meniscus lens Ll with a positive refractive power, with its convex surface facing the screen in order from the screen side.
The second lens L2, which has a biconvex shape, and its large concave surface face the screen.

The first lens includes a third lens L3 having a negative refractive power and serves as a field flattener.

The i2 lens and the 3rd lens are all made of plastic and are 1 each.
It has an aspheric surface that is larger than a surface and satisfies the following conditions. Note that plastics generally have a lower refractive index than optical lenses.

(1) 0.8f < drunkenness < 1.4f (2)
5f < ta < 31f (3) 0.85f < TT < 1.4f (4)
−1,3t <T;< −o, 5i(5) −
0,52f ([< -0,34f(6) O,13
f (Dl< 0.3f(7) 0.45f<0
2 < 0.6f (8) 0.24f < 03 <
0.4f (9) 0.5f < 04 < 0.7f
Paraxial radius of curvature of the surface on the screen side and the surface on the original image side of the two parts.

Correction and 11°: Paraxial radius of curvature of the screen-side surface and the original image-side surface of the second lens.

fo: Paraxial radius of curvature of the screen-side surface of the third lens.

Dl, axial thickness of the first lens D2: Distance between the first lens and the second lens on the axis.

D3: Axial thickness of the second lens.

D4: Distance between the second lens and the third lens on the axis.

f: Focal length of all prefectures.

However, the paraxial radius of curvature π is defined as follows. First, the shape of the aspheric surface is defined by H
is the height from the optical axis, and R is the radius of curvature of the vertex.

When A, B, C, D, E, A', B', C', and D' are aspherical coefficients and M is a displacement in the optical axis direction, it is expressed by the following equation.

+A'H3+B'H5+C'H7+D'H3 When the term A in this equation is not zero, the paraxial radius of curvature is as follows.

Next, each conditional expression and the extreme value a of the numerical range will be explained.

Conditional expression (1) relates to the radius of curvature of the screen-side surface of the first lens, and when the lower limit is exceeded, the first lens shares a large amount of power, and the angle of incidence of the off-axis light beam on the second lens increases. This becomes large, making it difficult to correct Huna aberrations and the like.

When the upper limit is exceeded, the power from the second renozu is 1 person
This makes correction of spherical aberration extremely difficult.

Conditional expression (2) relates to the radius of curvature of the picture tube side surface of the first lens and exceeds the lower limit.

The power of the second lens becomes large, making it difficult to correct spherical aberrations, and when the upper limit is exceeded, off-axis aberrations occur, making it difficult to correct aberrations.

Conditional expression (3) relates to the radius of curvature of the screen-side surface of the second lens, and when the lower limit is exceeded, off-axis aberrations, especially comatic aberrations, become large and difficult to correct. When the upper limit is exceeded, the share of the positive power of the surface of the second lens on the picture tube side increases, which increases the occurrence of spherical aberration, making it difficult to correct it.

Conditional expression (4) relates to the radius of curvature of the surface of the second lens on the picture tube side, and when the lower limit is exceeded.

The share of the power of the first lens increases, making it difficult to correct spherical aberration. When the upper limit is exceeded, off-axis aberrations, especially comatic aberrations and halos, become thicker and difficult to correct.

Conditional expression (5) relates to the radius of curvature of the third lens on the screen side; when the lower limit is exceeded, it becomes difficult to correct the field curvature, and when the upper limit is exceeded, it becomes difficult to correct the off-axis aberration.

Conditional expression (6) relates to the center thickness of the wtJl lens, and when the upper limit is exceeded, it becomes thicker than necessary, which is not desirable for correcting aberrations, and also increases production costs and causes a decrease in j/i degrees. becomes. When the lower limit is exceeded, the power of the first lens cannot be increased, so the burden of the positive refractive power of the second lens increases, making it difficult to correct aberrations.

Conditional expression (7) relates to the spacing between the first lens and the second lens, and when the lower limit is exceeded, the imaging power of the off-axis light beam is insufficient, and the second lens has a negative @ amount for the imaging of the off-axis light beam. This increases the angle of view, which becomes a major obstacle to widening the angle of view. When the upper limit is exceeded, the angle of incidence of the off-axis light beam on the rear surface of the second lens, that is, on the picture tube side becomes large, and the amount of aberration generated in the off-axis light beam becomes large.

Conditional expression (8) relates to the center thickness of the i2 lens,
When the lower limit is exceeded, the refractive power of the second lens is insufficient and w4
The burden of positive refractive power by one lens increases, making it difficult to correct one spherical aberration.

When the upper limit is exceeded, the refractive power of the second lens increases, making it difficult to correct aberrations.

Conditional expression (9) relates to the surface spacing between the second lens and the third lens; when the lower limit is exceeded, the power of the third lens increases, making it difficult to correct off-axis aberrations; The positive refractive power of the lens decreases, the burden of the positive refractive power of the first lens increases, and it becomes difficult to correct one spherical aberration.

Lens data of Examples will be described below.

In each description, R1, R2... is the radius of curvature of each lens surface, DI, 02... is the wall thickness or air gap between the lens surfaces, Nl, N2... is the e-line (wavelength 546...) of each lens. 1
refractive index for light (nm light), υ1. υ... is the Arabé number for the e-line. Also, the shape of the aspherical surface is
When the displacement in the direction of the optical axis is defined as Ma in the orthogonal coordinates, +A'H3+B'H5+C'H7+D'H! ! It is a symmetrical aspherical surface.

However, H: Height R from the optical axis Radius of curvature of the two-term point A, B, C, D, E, A', B', C', D': Aspheric coefficient.

[1! ! Value example 1] F=100 FNO=l:1.2 2W=6
5°R1= 332.99 DI=14.75
N1-1.49375 υ1=57.4R2=310
1.15 D2-60.09R3= 109.05
03=26.38 N2=1.49375 v2
=57.4R4=-95,00D4=50.66R
5=-91,9005=5.02 N5=1
．． 49375 υ3=57.416=929.1
5 06= 6.136R7= oo D7
-11.05 N4-1.54212 υ'4=5
9.5R8-5020,87 1st side 4th side 5th side A
3.0OX10-3 0. -4.6
5XIO-3B-2,02XIO-75,54X1
0-7 -5.74XlO-7C-L, 59X10-
11 -6.44XIO-113,82XIO-10
D-3,06XlO-16-9,17X10-16
-2.39XIO(3E -2,91X10-14
1 1.81XIO-1134, 26XIO-17A
'0. 0. 0°B
'O, O, O.

c'o, o,
o.

D'0. o,
o.

[Number f1 Example 2] F 100 FNOML: 1.2 2W
=65'R1 zero 196.45 I) l-27,7
1N1=1.49375 υ1=57.4R2 snow
541.38 D2=51.82R3-87,28
03 thousand 38.33 N2=1.49375 υ2=
57.4R4--129,0004-87,00R5 Gourd -53,7405-4,95N3 plot 1.49375
υ3=57.416--4125.75 06maro
1.31R7-oo D7-10.88 N4=
1.54212 v4-59.5uax 4946
．． 82 1st side 4th side 5th side A
1.08X10-3 0. - -4
．． 65XIO-3B-1,58XIO-73,8
4X10-7 1.15X10-GC-5,35X
IO-12-2,6X10-11 1.06X10-
10D-3,15XlO-16-1,1OXlo
-15-2,05XIO-13K -6,13X'
l0-19 7.11XIO-195,54X10
-17A' 0. 0.
O.

B10. O, O, c' o, o,
o.

D’　　　　0. O, O.

[Number 1111 Example 3] F=100 FNO=l:1.2 2W=6
5゜R1= 104.69 DI=29.40
N1-1.49375 υ1=57.4R2 95
6.06 D2=46.71R3=138.48
03-30.57 N2=1.49375 υ2
=57.414=-117.43 04-52.81R
5=-54,5705=5.02 N5=1
．． 49375 υ3=57.4Re−531.95
D6= 1.85R7-■ D7-11.04
N4-1.54212 υ4=59.5R8-5
017.07: jS1 side 4th side 5th side A
1.08Xlo-30, -4,65XlO-3B
-1,85X10-7 3.58X10-7
1.94X10-6C-1,70X10-12-
2.39XlO-11-3, 12X10-11D
-3,23Xlo-16-1,32Xlo-15-2,
0IX10-13E -1,53X10-18
-3.18XIO-189,90X10-17A '0
．． 0. O.

B'0. O, O.

c'o, o,
o.

D'O, O, O.

The longitudinal and lateral aberration diagrams in FIGS. 4, 5, and 6 sequentially show the optical performance of the projection lens portion (R1-R6) of Numerical Example 1.2.3.

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 3 are optical sectional views each showing an embodiment of the present invention. FIG. 4, FIG. 5, and FIG. 6 are aberration curve diagrams of each example. In the figure, Ri is a lens surface, Di is a lens surface interval of 1M is a meridional image surface, and S is a sagittal image surface.

Claims (1)

[Claims] (I) In a projection lens for enlarging and projecting an original image onto a screen, from the screen side, the convex surface faces the screen, and the first meniscus lens has a positive refractive power and the second lens has a biconvex shape. It consists of two lenses and a third lens with a negative refractive power that faces the screen with a concave surface with a large curvature, the first lens, the second lens,
The third lens is all made of plastic and each has one or more aspherical surfaces, and @R_1@ and @R_2@ are the paraxial curvature radius of the screen-side surface of the first lens and the side surface of the original image, @R_3@
and @R_4@ are the paraxial radius of curvature of the screen-side surface and original image-side surface of the second lens, @R_5@ is the paraxial radius of curvature of the screen-side surface of the third lens, and D_1 is the axis of the first lens. The upper thickness, D_2, is the distance between the axial surfaces of the first lens and the second lens,
A projection lens that satisfies the following conditional expression, where D_3 is the axial thickness of the second lens, D_4 is the axial distance between the second and third lenses, and f is the focal length of the entire system. (1) 0.8f<@R_1@<1.4f (2) 5f<@R_2@<31f (3) 0.85f<@R_3@<1.4f (4) -1.3f<@R_4@< -0.9f(5)-0
．． 52f<@R_5@<-0.34f(6)0.13f
<D_1<0.3f (7) 0.45f<D_2<0.6f (8) 0.24f<D_3<0.4f (9) 0.5f<D_4<0.7f However, paraxial radius of curvature @R @ is defined as follows. First, the shape of the aspheric surface is expressed in rectangular coordinates with the optical axis direction as the X axis, where H is the height from the optical axis, R is the radius of curvature of the apex, A,
When B, C, D, E, A', B', C', and D' are the aspherical coefficients and X is the displacement in the optical axis direction, @X@:R{1-√
(1-H^2/R^2)}+AH^2+BH^4+CH
^6+DH^8+EH^1^0+A'H^3+B'H^
5+C'H^7+D'H^9 When the term A in this equation is not zero, the paraxial radius of curvature is as follows. @R@=1/(1/R+2A)