JPH02167514A - Projection lens for projector - Google Patents

Abstract

PURPOSE:To obtain a high definition projector by composing the projection lens of 1st - 8th lenses, and providing the 6th or 7th lens with an aspherical surface. CONSTITUTION:The projection lens is composed of the 1st positive lens L1, 2nd positive lens L2, 3rd negative lens L3, 4th positive lens L4, 5th negative lens L5, 6th positive lens L6, 7th lens L7 which has a concave surface on the screen side and is weak in refracting power, and 8th negative lens L8 which has a concave surface on the screen side in order from the screen side. Then the 6th or 7th lens has the aspherical surface. Namely, the 1st lens L1 and 2nd positive lens L2 are provided to compensate an aperture aberration and further the 3rd negative lens L3 compensates a chromatic aberration which is generated by the 1st lens L1 and 2nd lens L2 and includes the power and also compensates a spherical aberration of high order. The 4th positive lens L4 is put in partial charge of the considerable part of the refracting power of the whole system and provides converging operation principally. The 5th negative lens L5 compensates a chromatic aberration which is generated by the 4th lens L4 and includes the power. Consequently, high-definition picture quality is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a projection lens, and particularly to a bright, high-definition projection lens suitable for a projection lens for a high-definition television projector.

(Prior Art) As is well known, a television projector is a device that enlarges and projects the screen of a cathode ray tube onto a screen using a projection lens, but in recent years there has been a demand for it not only for business use but also for home use. It's here.

On the other hand, so-called high-definition televisions, which have approximately twice the resolution of conventional televisions, are showing signs of being put into practical use mainly for commercial use, and are expected to become popular for home use as well. In this situation,
There is also a particularly high demand for high image quality in television projectors, and there has been a demand for television projectors that do not degrade the high-definition image quality seen on high-definition televisions.

In response to this demand, Japanese Patent Laid-Open No. 62-106 is a projector lens that attempts to obtain high-definition image quality.
Examples thereof can be found in Japanese Patent Application Laid-open No. 427 and Japanese Patent Application Laid-Open No. 62-85212. As is clear from the examples, these lenses include the first lens, a lens adjacent to it, etc.
By using an aspherical lens in the front lens group, spherical aberration and coma aberration caused by the aperture are corrected.

However, in reality, the technology for creating aspherical lenses cannot be said to have been perfected, and it is still extremely difficult to create them, and even when using aspherical lenses made of plastic, which is relatively easy to process. , environmental characteristics are inferior to glass lenses, so if an aspherical lens is used in areas where the aperture has a large effect on aberrations, such as the first lens or lenses adjacent to it, the effect on spherical aberrations will be large. The occurrence of high-order flare leads to a decrease in contrast and deterioration of image quality, making it difficult to realize a high-definition projector.

In order to solve this problem, it is conceivable to use a spherical lens in the front lens group such as the first lens or a lens adjacent thereto. However, in order to achieve high-definition image quality in terms of design, it has traditionally been considered essential to use an aspheric surface in the front lens group, so it was thought to be difficult to achieve this.

(Problems to be Solved by the Invention) However, as described above, various aberrations can be well corrected while using a spherical lens as the first lens, and high-definition television can be produced with a relatively small number of configurations. There is a strong demand for a projection lens for a projector that can provide high-definition image quality, and the present invention aims to provide a projection lens that can satisfy this demand.

(Means for Solving the Problems) As shown in the first construction drawing to FIG.
Lens, positive second lens, negative third lens, positive fourth lens, negative fifth lens, positive sixth lens, seventh lens with weak refractive power with concave surface facing the screen side, facing the screen side It is constituted by a negative eighth lens with a concave surface facing. and at least 1 on the 6th or 7th lens.
It has two or more aspherical surfaces.

In addition to having the above-mentioned basic configuration, the projector lens of the present invention preferably satisfies the following additional conditions.

(1) v, >45. ya2>4.5, v3<40
0.3<f/f〈0.7 0.5<f/f, <0.9 -1.5<f/f, <-1, O However, □: Atsushi number of the first lens 2 : Atsube number of the second lens v3: Atsube number f of the third lens : Focal length of the entire system fl: Focal length of the first lens f2: Focal length of the second lens f3: Focal length of the third lens f4: Fourth Focal length of lens f5: Focal length of the fifth lens 4: Atsube number of the fourth lens,: Atsube number of the fifth lens (3) 0.2<D/f<0.5 D=Third lens On-axis air distance f of the fourth lens: Focal length of the entire system (effect) The projection lens for a projector of the present invention has a positive lens and a positive second lens in order from the free-plane side, thereby eliminating aperture aberrations. It is well corrected. Furthermore, the negative third lens satisfactorily corrects chromatic aberrations including magnification generated by the first and second lenses, and also satisfactorily corrects higher-order spherical aberrations. The positive fourth lens shares a considerable part of the refractive power of the entire system, and mainly has a convergence effect.

The negative fifth lens corrects chromatic aberration including magnification caused by the fourth lens. The positive sixth lens is used to obtain better image quality in the periphery than in the middle of the screen, and particularly corrects coma aberration in the meridional direction from the middle to the periphery.

The seventh lens has a weak refractive power and has a concave surface facing the screen.
The negative eighth lens was used to obtain a better image surface. In particular, when the seventh lens is a spherical lens and the eighth lens is a spherical lens, the image plane can be well corrected and a good image plane can be obtained not only when the CRT phosphor screen has a curvature but also when the phosphor screen is flat. There is.

The sixth and seventh lenses have aspherical surfaces, and the former is mainly used for correcting meridional coma aberration at a wide angle of view, and the latter is used for good correction of the image plane.

Furthermore, as a condition for further improving practical performance, condition (1) is the Atsube number of the first lens, second lens, and third lens, the focal length of the entire system, and the first lens, second lens, and third lens. By satisfying this condition, chromatic aberration including magnification occurring in the first lens and the second lens can be well corrected.

Condition (2) is the Atsube number and focal length of the fourth lens, and the fifth lens.
These conditions are related to the Abbe number and focal length of the lens, and make it possible to satisfactorily correct axial chromatic aberration caused by the fifth lens, which has a considerable refractive power in the entire system.

Condition (3) is a condition regarding the axial air distance between the third and fourth lenses and the focal length of the entire system.If the lower limit of this condition is exceeded, the sagittal flare will increase significantly, and the contrast and resolution of the wide angle of view will deteriorate. decreases significantly. Furthermore, if the upper limit is exceeded, it becomes difficult to make the device compact, and when widening the field of view, it becomes difficult to obtain peripheral illumination, and it becomes difficult to obtain uniform image quality.

(Example) Examples of the projection lens for a projector of the present invention are shown below. The embodiment includes a biconvex first lens from the screen side, a positive meniscus second lens with the convex surface facing the screen side,
A negative third lens with a concave surface with a strong curvature facing in the opposite direction to the screen side, a positive fourth lens that shares a considerable portion of the refractive power of the entire system, a negative fifth lens, a positive sixth lens, and a screen. The seventh lens has a weak refractive power with a concave surface facing the screen, and the negative eighth lens has a concave surface with a strong curvature facing the screen.

Further, the sixth lens has an aspherical surface having an inflection point, and the seventh lens has an aspherical surface without an inflection point, and the first lens, the second lens, the third lens, the fourth lens,
The fifth lens and the eighth lens are composed of spherical lenses.

In the table, rl is the apex radius of curvature of the first lens surface from the screen side, d is the distance between the i-th lens surfaces from the screen side, rz is the refractive index at a wavelength of 543 nm of the i-th lens material from the screen side, Y; is Atsube's number. In addition, for an aspherical shape, in an orthogonal coordinate system with the origin at the apex of the surface and the optical axis direction as the X axis, the apex curvature is C1, the conic constant is K
, the aspheric coefficient is A1, and the power of the aspheric surface is P+ (P+>2
．． 0), it is expressed as φ=Jy +z.

In addition, the liquid layer Liq and face plate FP are shown in the table.
The value of is also indicative.

Example 1 Focal length f = 136.04 Half angle of view 21°05' Aperture ratio 1:1.2 Magnification 6.35x f/f□
=0.51 f/f2=0.75f/f, =-1
, 39 Aspherical coefficient on the I1th surface = 0.0 A 1 = -7,81559X10-'A2. =
7,02230X10-12A 3 = -4,570
50x 1O-15A 4 = -1,52311X
10-” on the I2 side = 0.0 A], = -2,62554X 1O-7A 2
= 1.07062 x 10-”A 3 = 3
．． 82736 x 10-”A 4. = -2,92
188X 10-” 13th surface K = -2,71719X 1O-1A1.= 3
．． 24894X10-7A 2 = -2,84276
X10-"A3= 7.41442X10-" A4 = -2,90580X 10-17 14th side power Pl= P2= P3= P4= P1= P2= P3= P2= P3= P4= 4.0000 6. 0000 8.0000 10.0000 4.0000 6.0000 8.0000 10.0000 4.0000 6.0000 8.0000 10.0000 = 1.31856 Example 2 Focal length f = 136.03 Half angle of view 20 '17' Aperture ratio 1:1.2 Magnification 6.9x f/f1=0
．． 54 f/f2=0.60f/f3=-1,24 f(+f,,, f,,)-0,013 L7'12 95.121 7.00 1.49425 55.0 '13 -1. 00.986 6.50 Aspheric coefficient on the 10th surface = 0.0 A 1 = -7,35810xlO-7A 2 =
-3,65500X10-”A3=9.849
40 X 1O-15A 4: -1,61460X
10-1B 1st plane = 0.0 A 1 = -2,33970X 1.0-'A2 =
4.30220X10-”A3=5.17890X10-”A4.
= -3,65070X 10-18 12th surface K = 4.01540

10.0000 4.0000 6.0000 g, ooo.

10.0000 2.71610xlo-7 -4,94340X 1.0-”?, 71990X 10”14 2.70880X 10-17 I P2= P3= P 4. = A1= A2= A3= On the 13th side = 1.70500 A 1 = -8,79020xlO-' P 1
=A2=-1,32130xlO-11P2
=A3= 1.34030X10-15P3=A4=
8.36760X10-” P4.=4.00
00 6.0000 g, ooo.

10.0000 4.0000 6.0000 8.0000 10.0000 Example 3 Focal length f = 136.01 Half angle of view 20'54' Aperture ratio 1:1.2 Magnification 6.35x f/f1
=0.56 f/f2=0.64f/f3=-1,2
5 d n Aspheric coefficient power A 2 = -3,87241X 1O-13A 3
= -3,18224X 10-”'A 4 =
-1,51116X10-11 + on the 12th side = 0.0 A 1 = -2,96426XIO-7A 2 =
1.03691 x 10”10A 3 = 3.
70839 X 1.0-”A 4 = -2,932
65X 10-11' 13th surface K = -3,97428X 10-”A 1 =
3.29946 X 1O-7A 2 = -4,53
491X 1O-11A 3 = 7.43436
X 10-”4A 4. = -2,90521X 1
0-” on the 14th side = 1.12002 P 2 = 6.0000 P 3 = 8.0000 P 4 = 10.0000 P 1 koP2 = P3 = P 4. = P1 = P2 = P3 = P4 = 4. 0000 6.0000 8.0000 10.0000 4.0000 6.0000 8.0000 10.0000 On the 11th page = OoO A 1 = -8,06844X10-7P1 = 4.0000 (Effect of the invention) The present invention is implemented As shown in the examples and various aberration diagrams, despite the large aperture ratio of about 1.2 and the wide half-field angle of about 21°, the imaging performance is good and the configuration is relatively simple. We have created a projection lens for projectors that can provide high-definition image quality similar to that of a high-definition television.

[Brief explanation of the drawing]

1 to 3 are sectional views showing the configurations of embodiments to 3 of the projection lens of the present invention, and FIGS. 4 to 6 are aberration diagrams of embodiments to embodiment 3, respectively.

Claims (1)

[Claims] In order from the screen side: positive first lens, positive second lens, negative third lens, positive fourth lens, negative fifth lens, positive sixth lens, refractive power with the concave surface facing the screen side. A projection lens for a projector, comprising a seventh lens with a weak curvature and a negative eighth lens with a concave surface with a strong curvature facing the screen side, and at least the sixth lens or the seventh lens has one or more aspherical surfaces.