JPS61213815A - Projection lens for television projector - Google Patents

Abstract

PURPOSE:To obtain a projection lens which has a large aperture of <=1.0 aperture ratio and 23-27 deg. wide field angle and has a good focusing capacity and does not require the mechanical temperature compensation, by constituting the projection lens with the first positive lens, the second positive lens whose surface opposite to the screen-side surface has a higher curvature, the third double convex lens, and the fourth negative lens whose screen-side surface has a high curvature which are arranged in order from the screen side. CONSTITUTION:A lens system is constituted to satisfy formulas (1) and (2) where (f) is the focal length of the whole of the system and f1 is the focal length of the i-th lens. It is desirable that conditions 1.5f<r4<-0.6f and 0.7f<r5<1.5f are satisfied where r4 is the radius of curvature at the apex of the surface opposite to the screen-side surface of the second lens and r5 is that of the screen-side surface of the third lens when the second or the third lens is a spherical lens. The formula (1) is the condition to make the image surface flat even if lens materials having a low refractive index are used, and the formula (2) is the condition to prescribe the distribution of the refracting power to the third lens on the assumption of the formula (1).

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a projection lens for a television projector, particularly to a projection lens for a three-tube television projector.

(Prior art) A television projector uses a projection lens to enlarge and project the screen of a shadow tube onto the screen, but the three-tube type projectors project the images of blue (B), green (G), and red (R). A color image is obtained by superimposing and projecting the screens of three shadow ray tubes with light bodies onto the screen using one lens each. In this case, there is no need for achromatization since each lens projects only one color of painter.

Plastic lenses are used in such lens systems due to the need for cost reduction and weight reduction.
No. 14, No. 57-34515, Kaikai No. 57-1088
No. 18, No. 177115 of 1983, etc. are known.

These are 3 sheets @ the number of sheets with little change, F number is 1, O
-1.3 large diameter projection lenses have been obtained.

In recent years, as projection lenses have become larger in size, lenses made only of plastic lenses have become problematic in that both projection edges deteriorate due to fluctuations in back focus due to warm changes in the reed of a television projector.

Possible temperature compensation methods to solve this problem include a focusing method that uses a mechanism that automatically moves the lens according to the chrominance change, and a device that keeps the temperature +i of the projection lens constant. In either case, it is impossible to prevent the device from becoming complicated and increasing the cost.

On the other hand, it has been proposed that the projection lens itself be configured by using a mixture of a spherical glass lens and a plastic lens to reduce the fluctuation in back focus caused by the measurement. Known examples of this are JP-A-58-118616, JP-A-58-12500, and JP-A-59-155818.

The lens of Shikashi, I'1lli No. 118616/1983 has large astigmatism. The lens of No. 58-125007 has good performance, but the iron also corrects aberrations by making both surfaces of the lens on the CRT side aspherical, so the purpose is to cool the CRT and prevent reflections. However, if the space between this lens and the CRT is filled with liquid, there is a problem that the performance at large angles of view will deteriorate. Furthermore, the lens disclosed in Japanese Patent Application Laid-Open No. 59-155818 has a disadvantage that it has a long overall length because it has a built-in mirror for refracting the optical path, and that the amount of peripheral light is small.

(Problems to be Solved by the Invention) This invention is a TV that has a large aperture ratio of 1.0 or less, a wide angle of view of 23 to 27, and has good performance but does not have the above drawbacks. The object is to obtain a projection lens for a projector.

Structure of the Invention (Means for Solving Problems) In this invention, as shown in FIG. 9, the focal length of the entire system is 1%, the focal length of the first lens is fi. , 1.1 < f < 1.7 ・・・・・・(
It is configured to satisfy the condition 2). In the figure, G represents the faceplate of the CRT.

Furthermore, let r4 be the vertex curvature radius of the surface of the second lens opposite to the screen, LSI< r4 < 0.6f ・-= (3)
When rs is the radius of apex curvature of the screen-side surface of the third lens and the second or third lens is a spherical lens, then 0.7f < rs <1.5f--(
It is desirable to satisfy the condition 4).

(Function) The lens of this invention is composed of three positive lenses and one negative lens, but the reason why the three positive lenses are arranged at intervals is to achieve as much symmetry as possible between the three positive lenses. This is to reduce the occurrence of coma aberration over a wide angle of view.

Condition (1) is the ninth condition that makes it possible to flatten the edge surface even if a lens material with a low refractive index is used. If the upper limit is exceeded, if the first to third lenses are made of an inexpensive material with a refractive index of 1.5 to 1.6, it is necessary to strengthen the negative refractive power of the fourth lens to prevent obstructions. There is. As a result, astigmatism becomes large, making it impossible to obtain a lens with a large aperture and a wide angle of view. K to correct this needs to be set to a refractive index t of at least one lens material of the first to third lenses of 1.65 or more. Among these types of materials, relatively inexpensive ones have a small Abbe number, which increases chromatic aberration, resulting in deterioration of the iron when a negative ray tube containing a phosphor with a wide spectral width is used. However, if you try to use a shadow ray tube that uses a phosphor with a narrow spectral width, such a shadow Ff tube has low brightness, so even if you use a large aperture projection lens, you will need a screen with a corner. It is not possible to obtain a television projector in which the brightness variation of both upper peaks is high.

Furthermore, lens materials with a refractive index of 1.65 or more and low dispersion are very expensive, leading to an increase in the cost of the projection lens.

If the lower limit is exceeded, while it is advantageous for image carrier formation, it has the disadvantage that the total length of the lenses becomes long in order to balance the amount of the first to third lenses.

Condition (2) is a condition that defines the distribution of refractive power to the third lens based on condition (1). When the upper limit is exceeded, sagittal flare increases, and performance at the periphery of the screen deteriorates with lenses with large apertures and wide angles of view.

When the lower limit is exceeded, inward comatic aberration becomes large in the periphery.

Line 1'l-(3) is for balancing coma aberration; when the upper limit is exceeded, inward coma becomes large, and conversely, when the lower limit is exceeded, outward coma aberration becomes large.

The lens of the present invention can be used as a projection lens for a television projector even when the second lens or the third lens is a spherical lens using a lens material with a refractive index of 1.5 to 1°6 as described above. A good lens can be obtained. If this material is glass, a glass material with a refractive index that varies to this extent has small dispersion and is relatively inexpensive. Projection lenses can be made inexpensively.

In this way, when the second lens or the third lens is a spherical lens, it is desirable to satisfy condition (4). Up@
If the lower limit is exceeded, the coma aberration at small angles of view will be too much, and if the lower limit is exceeded, the coma aberrations at small angles of view will be under. To compensate for these, the button needs to have more aspherical surfaces.

(Example) Examples of the projection lens of the present invention will be shown below.

In the table, rl is 11i in the apex curvature of the first lens surface from the screen side, and dl is the vertex curvature of the first lens surface from the screen side.
The distance between the lens surfaces, nl, is @1 from the screen side.
The refractive index of the th lens material, νi, is its Abbe number. In addition, for the aspherical shape, in an orthogonal coordinate system with the apex of the surface as the origin and the optical axis direction as the When the powers are Pl, P2, P3, P4, φ=G
; Represented by ding.

In addition, the saliva of the face plate G is also shown in the table.

Example 1? ”=116.50 Aperture ratio 11.oi ratio -0,1
25 Aspherical thread number/power number A3 = 3,801201)-13P3 = 6.000
0 Example 2 f=116.50 Ratio 1:1. O @ rate -0,12
5 Aspheric coefficient/power mosquito Example 3 f=116.51 Aperture ratio 1:0.9 Magnification -0,
125 Aspheric coefficient/power number A4 = 5.0899811!11 P4 = 6.00
00 Example 4 f=116.51 0 tonne ratio 1:1. Oe rate -0,125
Aspheric coefficient/power number Example 5 f=116.50 0 diameter ratio 1:1. Oi rate -0,125
Aspherical coefficient/power number example 6 f=116.50 Roku ratio 1:0.9 @ rate -0,12
5Aspheric coefficient/power number A4=-225139D-11P4=a0000 Effects of the invention As can be seen in the examples, the lens of this invention has a large aperture ratio of 1.0 or less, and an angle of view of 23 ~27
The imaging performance is also good, as shown in the aberration diagrams shown in FIGS. 2 to 7.

Furthermore, if the second or third lens is a spherical lens, and especially the third lens with a large refractive power is a spherical glass lens, changes in back focus due to temperature changes can be suppressed, and mechanical WA variation compensation can be achieved. Unnecessary.

In this case, as shown in the examples, good performance can be obtained even if a material with a refractive index of about 1.5 to 1.6 is used for the spherical glass lens. Glass with a refractive index of this level has low dispersion but is relatively inexpensive, so it is possible to create a lens with a large aperture and a large angle of view that is inexpensive and has little change in back focus due to changes in me. became.

Of course, when performing temperature compensation, the performance can be further improved by making all lenses plastic lenses and making them aspherical as appropriate.

[Brief explanation of the drawing]

@Figure 1 is a cross-sectional view showing the lens configuration of this invention, Figure 2,
wc3, FIG. 4, FIG. 5, FIG. 6, and FIG. 7 are aberration curve diagrams of Examples 1 to 6, respectively. Patent applicant Roku Konishi Photo Industry Co., Ltd. Patent attorney Fumi Sato (and 1 other person) Fig. 1 LIL2 L3 L4G Fig. 2 Spherical aberration Astigmatism Distortion aberration Meridional comatic aberration Fig. 3 Spherical aberration Aberration Astigmatism Distortion Aberration 14. Comatic Aberration Figure 4 Spherical Aberration Astigmatism Distortion Aberration 1.
) Onal coma w, Figure 5 Spherical aberration Astigmatism Distortion Meridional coma Figure 6 Spherical aberration Astigmatism Distortion Meridional e Coma Figure 7 Spherical aberration Astigmatism Distortion Meridional coma Aberration

Claims (1)

[Claims] From the screen side, a positive first lens, a positive second lens whose surface opposite to the screen side has a stronger curvature, a biconvex third lens, and a stronger surface on the screen side. It consists of a negative fourth lens with a curvature, and the focal length of the entire system is f, the i-th lens.
When the focal length of the lens is f_i, 1.05<Σ^3_i_=_1, f/f_i<1.41
．． A projection lens for a television projector, characterized by satisfying the following condition: 1<f_3/f<1.7