JPH01188814A - Projection lens for projector - Google Patents

Abstract

PURPOSE:To obtain a high picture quality from the center of a picture to a periphery by providing at least one aspheric surface at a first group lens. CONSTITUTION:The title lens is composed of a first positive group lens having the almost refracting power of the whole system successively from a screen side, a second negative group lens to direct a concave surface to the screen side and a third negative group lens and at least one aspheric surface is provided at the first group lens. Thus, a projection lens for a projector which is loaded to the projector to use a cathode ray tube in which a fluorescent surface is a plane, in which an aperture ratio is about 1:1.1 and larger, a semi- field angle is also about 28 deg. and wide, respective aberrations are satisfactorily corrected including a color and the image with a high picture quality is obtained up to the periphery.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a projection lens, and particularly to a projection lens for a projector used in a television projector or the like.

(Prior art) A television projector uses a projection lens to enlarge and project the screen of a cathode ray tube onto a screen.In recent years, projector devices have become more compact and are expected to become popular in homes. Along with this, there is a growing demand for further downsizing and cost reduction of projector devices.

At the same time, the projector lens also has an aperture ratio of 1:1.
There is a growing demand for extremely wide-angle lenses with a large aperture ratio of about 1 and a half-field angle of 28" or more.
Furthermore, the demand for higher quality screens is also increasing.

In order to meet such demands, lenses for projectors are disclosed in JP-A-60-49311 and JP-A-61-9.
613, JP 61-67812, JP 61-145517, JP 61-147213
Various types of devices have been designed, as seen in Japanese Patent Application Laid-Open No. 61-249014. However, these methods have a problem with the uniformity of image quality from the center of the screen to the periphery, and are therefore insufficient to meet the demand for higher image quality.

In addition, the achromatic effect, which was conventionally used for each color of R, B, and G and was not considered important in projection lenses for projectors, can be applied to the spectral distribution of the fluorescent screen of a cathode ray tube when higher image quality is required. The effects of this will become something that cannot be overlooked, so countermeasures against one color will also be necessary.

Furthermore, by making the phosphor screen of a cathode ray tube into a shape other than flat, it is possible to cancel field curvature and widen the angle of view, as disclosed in Japanese Patent Application Laid-open No. 60-43627 and Japanese Patent Application Laid-open No. 60-200.
No. 215, JP-A-61-145516, JP-A-62-71915, etc. can be found. However, these methods use a cathode ray tube with a special shape different from the commonly used cathode ray tube with a flat fluorescent screen, which is technically difficult and disadvantageous in terms of cost.

Therefore, there is a need for a projection lens for a projector that uses a currently commonly used cathode ray tube with a flat phosphor screen, has high performance from the center to the periphery of the screen, and can be made at a low cost.

(Problem to be solved by this invention) This invention is installed in a projector using a cathode ray tube, which has a flat phosphor screen and has an aperture ratio of 1:1.1.
The objective is to obtain a projection lens for a projector that has a wide half angle of view of approximately 28 degrees, has all aberrations including color well corrected, and can provide high-quality images up to the periphery. .

(Means for solving the problem) The projection lens for a projector according to the present invention has the following features:
As shown in Figures 3 and 3, in order from the screen side, the positive first group lens has the most refractive power of the entire system, the negative group II lens with its concave surface facing the screen side, and the negative mth group lens. It is characterized in that the first group lens is provided with at least one aspherical surface.

Further, in the above basic configuration, the first group lens is composed of four lenses: a positive first lens, a negative second lens, a positive third lens, and a fourth lens, and 0.3 < f/
f2. , < 1.5 ・ ・ ・ ・
(1) 0.5 < f/lfg, ml < 2.0
... Characterized by satisfying the condition (2).

However, f 2 @ 3 : Composite focal length fl of the 2nd lens and 3rd lens constituting the 1st group lens, = : Composite focal length of the 1st group lens and m-th group lens f : Composite focal length of the entire system Further ν1)50. ν,〈45, ν,〉50 ・
・・ (3) 1.0 < f/fm < 0.0 ・
...(4) However, S: Atsube number of the first lens in the i-th group lens 2: Atsube number of the second lens in the first group lens 3: Atsube number of the third lens in the first group lens f1: Focal length of the ■th group lens f: It is desirable to satisfy the conditions for the focal length of the entire system.

In addition, the above-mentioned Ⅰth group lens has a relationship of 0.0<DI/DI<2.0 with respect to the 1st group lens and the m-th group lens (5)
However, DI: Distance between the first group lens and the ■th group lens DH = the ■th group lens
It is desirable that the condition for the distance between the group lens and the m-th group lens be satisfied.

(Function) The basic configuration of the lens of this invention is a first group lens having at least one aspherical surface in order to satisfactorily correct aberrations caused by the aperture, a negative group lens with a concave surface facing the screen, and a negative By using two field curvature correction lens groups, the ■th group lens and the mth group lens, for the first group lens, which has almost the entire refractive power The surface has been well corrected.

Up until now, the construction of a projection lens for a projector has generally consisted of a 1' group lens which has most of the refractive power of the entire system, and a 1'
Many of them consisted of a 1' group lens as one image plane correction lens group. In such a configuration, the Petzval sum P of the entire system is equal to the Petzval sum P of the 12th group lens.
I+ and the Petzval sum PI' of the lens of the 2'th group are expressed by the following equation.

P=Pl'+PM'−−−・−(a) Here, the role of canceling the Petzval sum PI′ generated in the first group lens, which has most of the refractive power of the entire system, is the negative
The Petzval sum Pl' of the ' group lens must be responsible. By the way, such an image plane correction lens group is used in a generally widely known projection lens for a projector.

Like the No. 2 lens shown in the embodiments of this invention, it is often an immersion lens; in this case, the Petzval sum P++' in equation (a) is Pw'4(nm'-x
1)/(rl+', i'rg'-z)" (b) where nl', 1: refractive index rl' of the first lens of the first group lens
, 1: Expressed by the radius of curvature of the screen-side surface of the first lens of the lens group ■'.

By the way, as is clear from this equation (b).

In such a configuration, the
.

The degree of freedom of the lens is small, which is disadvantageous in correcting aberrations.

For example, if a glass material with a low refractive index is used for the first lens in the first lens group, the curvature of the side surface of the screen of the first lens in the first lens group will become stronger, which will reduce the effect on other aberrations such as distortion. As the size increases, performance deterioration becomes unavoidable.

On the other hand, with the configuration of the present invention, the Petzval sum P of the entire system is the Petzval sum P1 of the first group lens. It is expressed by the following equation using the Petzval sum PI of the 1st lens group and the Petzval sum P 2 of the mth group lens.

P=P++Pm+Pm・ @ @ + e (
c) The role of canceling out the Petzval sum PI generated by the first group lens, which has most of the refractive power in the entire system, is the Petzval sum PI of the negative second group lens and the Petzval sum P1 of the negative mth group lens. is sharing the burden. For example, as in one example shown in the examples, even in a simple configuration in which the lens group Ⅰ is a single negative lens with its concave surface facing the screen side, the term p, +P 厘 in equation (c) is, however, rl, □: radius of curvature rB of the screen-side surface of the first lens of the ■-th group lens, 2: radius of curvature r-rin of the surface of the first lens of the ■-th group lens opposite to the screen side, 1: Radius of curvature n of the screen-side surface of the first lens of the m-th group lens: Refractive index n1 of the first lens of the (2)-th group lens: Refractive index of the first lens of the m-th group lens.

As is clear from this equation (d), the first lens of the m-th group lens
The second group lens provides sufficient freedom to provide an appropriate value for image plane correction while minimizing the influence of the radius of curvature of the side surface of the lens screen on other aberrations such as coma. However, in this case, since the (1)-th group lens is farther from the image plane than the m-th group lens, it has a greater influence on other aberrations such as coma to difference than the m-th group lens. Therefore, in order to keep this effect to a minimum in terms of aberration correction,
The group lens has a concave surface facing the screen and is arranged close to the image plane.

When the above basic configuration is satisfied and the first lens group is composed of four lenses: a positive first lens, a negative second lens, a positive third lens, and a fourth lens.

Condition (1) concerns the ratio of the combined focal length of the second and third lenses that make up the first lens group to the focal length of the entire system; if the upper limit is exceeded, the extroverted coma aberration becomes large at a wide angle of view. If the lower limit is exceeded, inward coma aberration becomes large at wide angles of view.

Even if coma aberration is corrected at a wide angle of view by the fourth lens, both of which constitute the first lens group, deterioration in image quality cannot be avoided.

Condition (2) relates to the combined focal length of the n-th group lens and the n-th group lens and the focal length of the entire system.If the upper limit is exceeded, the image plane will be over-corrected, and if the lower limit is exceeded, the image plane will be under-corrected, resulting in a flat image surface. becomes difficult to obtain.

Condition (3) is that the first lens and the second lens constituting the first lens group
This relates to the Abbe number of the lens and the third lens, and by satisfying this condition, it is possible to satisfactorily correct chromatic aberration.

Condition (4) relates to the focal length of the n-th group lens and the focal length of the entire system, and better image plane correction is possible within this range.

Condition (5) is a condition regarding the distance between the first group lens and the nth group lens and the distance between the nth group lens and the nth group lens,
Within this range, it is possible to effectively correct aberrations by the n-th group lens.

Further, the fourth lens is effective in favorably correcting coma aberration at a wide angle of view, and is particularly effective when it has one or more aspherical surfaces.

(Example) Examples of the present invention will be shown below. The symbol in the table is rI: radius of apex curvature d of the i-th lens surface from the second screen side + interval n i of the i-th lens surface from the second screen side + refractive index of the i-th lens material from the screen side at a wavelength of 543 nm Indicates the Atsube number of the i-th lens material from the Shimini screen side. Also, for an aspherical shape, the apex curvature is C1, the conic constant is K, in the orthogonal coordinate system with the origin at the apex of the surface and the optical axis direction , the aspherical surface coefficient is A1. When the power of the aspherical surface is Pi CP+>2.0), x=c'', 1+v'1-(1+k)...
It is expressed as φ=v-75=17. Note that the table also shows the value of the face plate FP, which is included in the n-th group lens.

Example 1 f = 104.71 Aperture ratio = l: 1.1 Magnification -
0,13423f/f,,,=0,47
f/lf3. Maro 1 = 1.24f / f *= -
0.23Dm/D+=0.62i r+
d+ old month G, 1 106
．． 63g 14,00 1,49305 572
-1358.731 23.513 -573.2
00 3.00 1.59061 304 87
．． 584 1.30 5 87.154 30.93 1.59162
61.26 -112.544 6.51 7 143.058 10.00 1.49305
57 & -4715,47933,93Gw
9 -118.612 3.00 1.4930
5 5710 -258.429 21.00Gm
11 -53.549 4.00 1.51g
41 64.112 Liq-200,00015,
991,4119013FP ω 7.00
1.5423014 ■ Aspheric coefficient Power number 1st surface K = 1.93320 X 10”1A 1 =
-8,34730X 10~' PL=4.00
00A2= -4,11700X10”” P2=
6.0000A3=-9,50790xlO-”
P3=8.0000A4=4.6482
5X10-” P4 = 10.0000 2nd surface K = -3,07914X 103A1 = -7,
54921xlO-' P1= 4.0000A
2=-3,13167X10-” P2=6
．． 0000A3=-3,26887xlO-”
P3= 8.000CIA4= -9,36941x
lO-" P4= 10.0000 on the third side= 1.11049X10" A1= -1,75981X10-' P1=
4.0000A2= 4.63476X10-”
P2=6.0000A3=5.80542x
tO-14P:3=a,ooo.

A4=-1, I2035X10-17P4=10. OO
On the 7th side of O0: 0.0 A1= 3.20882X10-' Pl=
4.000OA 2 = 5.50784 x 10
"" P2= 6.0000A3= 4.27
444X10-14P3= 8,0000A4=
5.74042XIO-” P4= 10.000
0 on the 8th side= 1.83448X10" A1= -1,78411X10-' P1=
4.0000A2=5.34312X10-1″
P2=6.0OOOA3=2.88882X10
-” P3=8.0000A4=-2,118
78XIO-" P4 = 10.0000 on the 9th side = 1.92461 A1 = -5,50240XIO-" P1 =
4.0000A2=2.36741X10-'
P2: 6.0000A3=-2,02964X1
0-i3P3= 8.0000A4=-2,069
34xlO-" P4 = 10.0000 10th surface K = -4,83108 A1 = -4,70693X10-" P1
= 4.000OA2= 2.56713xlO
-' P2= 6.0000A3= -5
,79526xlO-” P3=8.00
00A4=-1,55258x10-” p4
= 10.0000 Example 2 f = 104.26 Aperture ratio = 1:1.1 Magnification -
0,13423f/f,,,=0.82 f/th'g,gl=1.21f/f i=0.03
Da/D+=1.14i r+d
In+ v+G+ 1 73.917
19.75 1.49305 572 351.5
71 24.48 3 1048.003 3.50 1,59061
304 134.309 10.00 5 93.887 30.00 1.59162
61.26 -113.254 8.74 7 3780.610 6.25 1.49305
578 1171.790 19.11G@9
-250.000 3.00 1.49305 5
710 -300.000 21.75G ■ 11
-56.023 4.00 1.62444 3
6.312 Liqoo 15,99
1.4100013 FP (X)
7.00 1.54230 Aspheric coefficient Power number 1st surface K = 1.59500 X 10-”A1= −
1,0O050X10-' P1= 4.000
0A2= -2,34830X10-” P2=
6.0000A3=4.97640xlO-1s
P3= 8.0OOQA4= -z, 54otoXi
o-" P4= 10.0000 2nd surface K = 4,28870 x 10 A1= 2.13470xlO-' P1=
4.0000A2=-2,40120X10-”
P2= 6.0000A3= 6.85610X
10-” P3=8,0000A4=-1,8
5600X10-” P4=10.0000 3rd surface K=1.00000 X 10”A1=-2
,99030xlO-' P1= 4.0000
A2= -1,28520xlO-” P2=
6.0000A3=-3,53380xlO-14
P3= 8.0000A4= 1.39550X
10-17 P4= 10.0000 4th surface K 5 -4.49960 A1= 6.92150X10-” P1=
4.0000A2=-1,02260X10-”
P2=6.0000A3=-7,34730X
10-14P3= 8.0000A4= 2,50
930X10-” P4= 10.0000 7th surface K= 7.94400 X 1O-1AI=-4,
15480X]0-7PI=4,000OA2=-
9,02860X10-1aP2=6.0000A
3= 8.80470X10-14P3= 8.0
000A4=-1,28300X10-” P4=
10.0000 on the 8th side = 2.2086 A1 = 1.22870X10-' P1 =
4.000OA2=-1,00550X10-'
P2= 6.0000A3= 2.31930X
10”13P3=8.0000A 4=-3,
92470X 10-' P4= 10.0000
Example 3 f=104.96 Aperture ratio=1:1.1 Magnification -0
,13423f/f,,2=0.83f
/ I f ++, sl = 1.16f/fm = -
0.08Dm/D+=1.10i rl
d+ n+ 91G+ 1 7
3.586 19.75 1.49305 572
346.601 23.87 3 1141.431 3.50 1.59061
304 134.884 10.00 5 94.873 30.00 1.59162
61.26 -111.062 8.74 7 3780.610 6.25 1.49305
578 1171.900 19.72GW
9 -202.421 3.00 1.4930
5 5710 -300.000 21.75G*
11 -56.041 4.00 1.624
44 36.312 Liq-200,00015,
991,4119013FP ω 7.00
1.5423014 o.

Aspheric coefficient power number 1st surface K = 1.59500 x lo-”A1= −
1,01533X10-' P1= 4.000
0A2=-2,28256X10-” P2=
6.0000A 3 = 4.97704 X 1
0-” P3= 8.0000A4=-2,5
4009xlO-” p4= 10.0000 2nd
Surface K = 4,28870 x 10Al = 2.
13470X10-' Pl=4.0000A
2=-2,40120X10-11P2=6.00
00A3= 6.85610xlO-1sP3=
8.0000A4=-1,85600xlO-”
P4=10.0000 3rd surface K: 1,00000 x 102A1=-2,
99030X10-7PL=4.0000A2=-
1,28520xlO-10P2=6.0000A
3=-3,53380XlO-” P3=8
．． 0000A4=1.39550xlO-17P4
= 10.0000 on the 4th side = -4,49960 A1 = 6.92150X10-" PL =
4.0000A2=-1,02260X10-
” P2= 6.0000A3= -7,
34730xtO-” P3=8.000
0A4= 2.50930X10-17 P4
= 10.0000 7th surface K = 7,94400 X 10-'Al= -
4,15480XIO-' P1= 4.000
0A2= -9,02860XIO-” P2=
6.0000A3=8.80470xlO-14
P3=8.0000A4=-1,28300X10
-” P4 = 10.0000 on the 8th side = 2.20860 Al = 1.0ri038X10-' PL =
4.0000A2=-1,00390X10-'
P2 = 6.0000A 3 = 2.3194
6X10-13P3=8.0000A4=-3,9
2469xlO-17P4 = 10.0000 on the 9th side = 1.25665 Ai = -2,47735X10-" pt = =
4.0000A2=8.59415xlO-”
P2 = 6.0000A 3 = 3.674
16XIO-” P3= 8.0000A4
= 1.17507X10-” P4=
10.0000 (Effects of the Invention) As seen in the above embodiments and drawings, this invention has a large aperture ratio of about 1.1 and a wide half angle of view of about 28 degrees. The imaging performance was also good as shown in the various aberration diagrams, and it was possible to obtain a projection lens for a projector that could provide high image quality from the center to the periphery of the five screens.

Note that, as shown in the embodiments, by using a composite lens of a meniscus lens and a liquid lens as the second group lens, it is possible to further reduce the cost in mm.

[Brief explanation of the drawing]

1 to 3 are sectional views showing the structure of a projection lens for a projector according to the present invention, and FIGS. 4 to 6 are aberration diagrams of Examples 1 to 3, respectively.

Claims (1)

[Scope of Claims] 1) Consisting of, in order from the screen side, a positive group I lens having most of the refractive power of the entire system, a negative group II lens with its concave surface facing the screen side, and a negative group III lens. , a projection lens for a projector, characterized in that the I-group lens has at least one aspherical surface; 2) In the projection lens for a projector according to claim 1, the I-group lens is a positive first lens; Consisting of four lenses: a negative second lens, a positive third lens, and a fourth lens, 0.3<f/f_2_・_3<1.5 0.5<f/|f_II_・_III|<2. A projection lens for a projector that satisfies the condition of Composite focal length f of group lens: Composite focal length of the entire system