JPH01266504A - Projection lens for projector - Google Patents

Abstract

PURPOSE:To reduce the cost and to improve the performance by composing a 1st lens group of only spherical lens elements, arranging at least one of negative lenses in the 1st lens elements so that its concave surface face a positive lens on a screen side, and providing a 2nd lens group or 3rd lens group with >=1 aspherical surface. CONSTITUTION:The aberrations due to an aperture is compensated excellently by the 1st lens group G1 which contains at least one positive lens and at least one negative lens and at least one of negative lenses in the 1st lens group G1 has its concave surface facing the positive lens adjoining to the screen side to compensate the comatic aberration. The negative lenses in the 1st lens group G1 also compensates the chromatic aberration of the power and on-axis chro matic aberration excellently. The majority of the refracting power of the whole system is determined by the 2nd lens group G2, which provides intense converg ing operation. Aspherical surfaces are employed for the 2nd lens group G2 and 3rd lens group G3 and then various aberrations generated by the 2nd lens group G2, mainly, the comatic aberration corresponding to a wide field angle can be compensated excellently and effectively. Consequently, the cost is reduced and the performance is improved.

Description

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

(Prior Art) A television projector is a device that enlarges and projects the screen of a cathode ray tube onto a screen using a projection lens, and in recent years, demand has been expected not only for business use but also for home use. Along with this, there has been an increasing demand for compact and low-cost projector devices, and projector lenses have a large aperture ratio of about 1.04 and a half-field angle of 28.
It has become necessary to have an extremely wide angle of view, with an angle of view of more than 100°.

On the other hand, there is a growing demand for higher image quality, and red (R)
Since three cathode ray tubes (green (G), blue (B)) are used, and each image is projected by a separate projection lens, the projector lens, which used to only require correction of monochromatic aberration, now requires correction of chromatic aberration. The need has arisen.

One conventional example of a projector lens used for such a purpose is the one described in Japanese Patent Application Laid-open No. 62-94811, which has an aperture ratio of 1.4 and a half diameter. Since the angle of view is also narrow at about 24°, it has not been possible to satisfy the recent demands mentioned above.

In addition, many projector lenses that use many aspherical surfaces have become known in order to reduce costs. especially,
In order to properly correct aberrations caused by the aperture, it has been considered essential to use an aspheric surface in the first lens group when viewed from the screen side.

However, even today, aspheric lenses still have many technical difficulties. For this reason, when an aspherical surface is used in the first lens group, which is particularly effective for correcting aberrations caused by the aperture, the reproducibility of design performance during actual projection is poor. This is because, although the aspheric surface of the first lens group has a large aberration correction effect, the influence of the error is also greater than when it is used in other groups. In order to improve this, the first step is to
It is necessary that the lens group has no aspherical surfaces. Therefore, there has been a demand for a projection lens for a projector with a large aperture ratio and a wide angle of view, which can satisfactorily correct various aberrations without using an aspheric surface in the first lens group.

In response to this request, Japanese Patent Application Laid-Open No. 61-2417
A projector lens using a spherical lens in the first lens group is described in Japanese Patent No. 17. However, as is clear from the structure of this lens, the first lens group is nothing but a modified Gauss type first lens, and Gauss type lenses generally have small spherical aberration. The characteristics are used to correct aberrations and coma due to the aperture, but this configuration requires at least four positive lenses and two negative lenses to form a Gaussian type, and the convergent lens group and image plane Including the correction lens group, at least eight or more lens elements are required.

Also, as seen in the example, a positive lens has a refractive index of 1
．． 69 or higher, a negative lens uses a glass material with a high refractive index of 1.75 or higher, resulting in a very high cost.

(Problems to be Solved by the Invention) Therefore, there is currently a need for a projection lens for a projector that can satisfactorily correct various aberrations and can be made at low cost while using a spherical lens as the first lens group. It is rare. The present invention aims to provide a projection lens that can satisfy such demands.

(Means for solving the problem) As shown in FIG. 1, the projection lens for a projector of the present invention includes a first lens group including at least one positive lens and at least one negative lens from the screen side; a second lens group having refractive power; a third lens group having negative refractive power;
The first lens group consists of only spherical lens elements, at least one of the negative lenses in the first lens group has a concave surface facing the positive lens adjacent to the screen side, and the second lens group Alternatively, the third lens group is configured to have at least one aspherical surface.

As supplementary conditions for implementing the present invention more effectively, it is desirable to satisfy the following conditions.

(1) ν,”>50. ν1〉50 However, ν1
''': Atsube number ν1 of the positive lens constituting the first lens group; Atsube number ν1 of the positive lens constituting the second lens group (2) In the projection lens for a projector of the present invention,
At least one plastic lens is used as a lens constituting the second lens group.

(3) In the projection lens for a projector of the present invention,
At least one plastic lens is used as a lens constituting the first lens group.

(4) In the projection lens for a projector of the present invention,
The second lens group includes at least two positive lenses.

(5) In the projection lens for a projector of the present invention,
A surface of the first lens group adjacent to the second lens group has a concave surface facing the second lens group.

(Function) The present invention provides a first lens group including at least one positive lens and at least one negative lens that satisfactorily corrects aberrations due to the aperture, and that at least one of the negative lenses in the first lens group is located on the screen side. The concave surface faces the adjacent positive lens, effectively correcting coma aberration. Furthermore, the negative lens in the first lens group also performs good correction of chromatic aberration of magnification and longitudinal chromatic aberration. The second lens group shares a considerable portion of the refractive power of the entire system, and has a strong convergence effect. The third lens group includes a negative lens used to obtain a flat image surface, and has the function of correcting the Petzval image surface that cannot be corrected in the first and second lens groups. In addition, by using aspheric surfaces in the second and third lens groups, various aberrations that occur in the second lens group, which has a strong convergence effect, can be well and effectively corrected, mainly coma aberration at wide angles of view. is being carried out.

In addition, condition (1) is a condition for making the implementation of the present invention more effective, and is a condition regarding the Abbe number of the positive lens in the first lens group and the Abbe number of the positive lens in the second lens group, and is a condition for correcting chromatic aberration. It is effective to satisfy this condition.

Condition (2) relates to the glass material of the lenses constituting the second lens group, and is intended to reduce costs by using plastic lenses.

Condition (3) relates to the glass material of the lenses constituting the first lens group, and is intended to reduce costs by using plastic lenses.

Condition (4) is a condition regarding the lenses constituting the second lens group, and by having the second lens group include at least two positive lenses, it is possible to reduce the occurrence of various aberrations due to the convergence effect. can.

Condition (5) is related to the shape of the surface of the first lens group adjacent to the second lens group, and the Petzval sum can be reduced by directing the concave surface toward the second lens group, which has a strong convergence effect. , is effective for performing image plane correction.

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

In the table, ri is the apex radius of curvature of the first lens surface on the screen side, d is the distance between the first lens surfaces from the screen side, n= is the refractive index of the first lens material from the screen side at a wavelength of 543 nm, It is the Atsube number other than ν11. In addition, for an aspherical surface shape, in an orthogonal coordinate system with the apex of the surface as the origin and the optical axis direction as the
>2.0), it is expressed as φ=7y king core.

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

Example 1 f=104.6 Aperture ratio 1:1.04 Magnification -0.1
342 Half angle of view 28 @ rI dI Old νI aspherical coefficient On the 9th power plane = 0.0 A 1 = -3,20750x 10-' P
1 = 4.0000A 2 = 3,5977
5 x 10-11 p2 = 6.0000A
3 = -1,61368X 10-” P 3
= 8.0000A 4 = 2.71444
X 10-” P 4 = 10.0000 on the 10th side = 0.0 A 1 = 1.78226X10-7 P
1 = 4.0000A 2 = -1,8761
1X10-10 P2 = 6.0000A 3
= 8.10776X10-” P 3 =
8.0000A 4 = -1,22963X1
0-” P 4 = 10.0000 Example 2 f = 103.8 Aperture ratio 1:1.04 Magnification -0.1
342 half angle of view 28.4" rIdB Old ν1 Aspherical coefficient To the 7th power plane = 0.0 A 1 = -9,42287X 10-" P
1 = 4.0000A2 = -4,75003X1
0-11P2=6.0000A 3=-2,
02886X 1O-14P 3 = 8.0000
A4 = 4.61696 x 10-”P
4 = 10.0000 on the 8th side = 0.0 A l = 3.02455 X 10-'
P L = 4.0000A2 = -6,26202X
10-11P2 = 6.0000A 3 = -4
, 24755X 10-” P 3 = 8.0
000A 4 = 1.64579 x 1O-1
7P 4 = 10.0000 9th surface K = 0.0 A l = 6.03308 X 10-”
P 1 = 4.000OA2 = 2.5881
7X10-11P2 = 6.0000A 3 =
-2,50325X 1O-14P 3 = 8.0
000A 4 = 2.44141 x 10-”
P 4 = 10.0000 on the 10th side = 0.0 A 1 = 2.90569 X IP' P
L = 4.0000A 2 = -5,7265
3X 1O-11P 2 = 6.0000A3=:
7,21163X10”” P3= 8,00
00A4= -3,29113X10-” P4=
10.0000 Example 3 f=106.1 Aperture ratio 1:1.04 Magnification -0,1
342 half angle of view 29.2゜ri d+ old ν1LI
O-178,65445,26 Aspheric coefficient On the 11th power plane = -7,36044x 10-”A l =
-2,45469X 10-' P 1 = 4
．． 0000A 2 = 1.22572 x 10-
”P2=6.0000A3=4.41
192xlO-” P3= g, ooo.

A 4 = -6,83221X 10-”P
4 = 10.0000 (Effects of the Invention) As shown in the examples, the present invention has a large aperture ratio of 1.04, a wide half angle of view of 28° or more, and imaging performance as shown in Figures 2 to 4. As shown in the aberration diagram shown in Figure 2, the results are good. Further, the present invention prevents an increase in cost by making it possible to use lenses with low refractive indexes, such as the positive lens having a refractive index of 1.68 or less and the negative lens having a refractive index of 1.75 or less, as in the embodiments.

Although the third lens group G3 is a very large negative lens, which increases the cost, it is possible to make it a composite lens of a meniscus lens and a liquid lens by slightly modifying the embodiment, and it is possible to make it a composite lens of a meniscus lens and a liquid lens. By changing the design, it is possible to reduce the cost of the lens, prevent reflection between the CRT side surface of the third lens group and the face plate surface, and increase the contrast of the projector device.

Further, the cost of the meniscus lens can be further reduced by using a plastic lens, and the performance can be improved by using an aspheric surface.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of the projection lens of the present invention, and FIG.
Figures 3 and 4 are Example 1 and Example 2, respectively.
and FIG. 7 is an aberration diagram of Example 3.

Claims (1)

[Claims] From the screen side, the first lens group includes a first lens group including at least one positive lens and at least one negative lens, a second lens group having positive refractive power, and a third lens group having negative refractive power. The group consists of only spherical lens elements, and at least one of the negative lenses in the first lens group has a concave surface facing the positive lens adjacent to the screen side, and at least one of the negative lenses in the second lens group or the third lens group A projection lens for a projector, characterized by having one or more aspherical surfaces.