JPS6394214A - Refractive type projection lens - Google Patents

Abstract

PURPOSE:To improve chromatic aberration and focus movement due to temperature change by constituting a refractive type projection lens consisting of three groups of plastic and glass lenses and especially constituting a 2nd group of a plastic junction lens and a glass single lens. CONSTITUTION:The projection lens is constituted of plastic and glass lenses and a 1st group including a meniscus lens 1 having convex faces on both sides, the 2nd group consisting of a plastic junction lens 2 and the glass single lens 3 and a 3rd group consisting of a negative lens 4 having a concave face on the screen side are arranged successively from the screen side. The chromatic aberration is corrected by mainly the plastic junction lens 2 in the 2nd group and then focus movement generated by temperature change is corrected mainly by the glass single lens 3 in the 2nd group. Consequently, the chromatic aberration and the focus movement due to the temperature change can be improved and the weight of the whole lens system can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a refractive projection lens, and more particularly to a refractive projection lens for use in a projection television system that projects images from a projection tube (e.g., C, R, T, etc.) onto a large screen. Regarding formula projection lenses.

(Prior art) Projection television systems have blue, green,
Red A projection lens is placed in front of each of the three color projection tubes, and the images on the projection tubes are projected by the projection lenses onto a screen placed in front of the projection lens to synthesize the images of the three colors. The resolution on the screen is said to be around 0.21ps/*vr, which is sufficient.
Furthermore, since the width of the emission spectrum of the phosphor of the projection tube is narrow, it has been thought that there is little need for chromatic aberration correction of the projection lens for general consumer use.

Furthermore, the focal point of the projection lens may shift due to temperature changes, but the image quality has been set to be the best at the operating temperature.

(Problems to be Solved by the Invention) However, recently there has been a strong demand for lenses with even higher resolution, and a projection lens with corrected chromatic aberration has become necessary.

On the other hand, in response to the demand for high-resolution lenses, it has become necessary not only to correct chromatic aberration but also to improve image quality deterioration due to focal shift caused by temperature changes.

If the projection lens were entirely composed of glass lenses, it would be relatively easy to meet the above-mentioned request, but this generally requires 6 to 7 glass lenses, which is undesirable in terms of cost and weight.

Therefore, the present applicant developed a so-called hybrid type projection lens consisting of a plastic lens and a glass lens, and filed a patent application on October 9, 1985.
No. 225665, title of invention: refractive projection lens). The projection lens of the present invention is composed of a first group consisting of a meniscus lens, a second group consisting of a cemented glass lens, a single glass lens, or a plastic aspherical lens, and a third group consisting of a concave lens. This projection lens is
The second group has the main lens power, and mainly corrects chromatic aberration with a glass cemented lens, and corrects focal shift due to temperature changes with a single glass lens. However, in this projection lens, since the main part of the second group having the main lens power is made of a glass lens, it does not meet the requirements of being lightweight and low cost.

The present invention has been made in view of the above-mentioned points, and its purpose is to provide a projection lens that is lightweight and inexpensive, as well as improving chromatic aberration and focus shift due to temperature changes.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention comprises a projection lens composed of a plastic lens and a glass lens, and includes meniscus lenses having convex surfaces on both sides with respect to the screen in order from the screen side. The first group, a plastic cemented lens,
For the second group consisting of a single glass lens and the screen,
This lens is characterized by being comprised of a third group consisting of a negative lens having a concave surface.

(Function) Chromatic aberration is mainly corrected by the plastic cemented lens in the second group, and focal shift caused by temperature change is corrected mainly by the single glass lens in the second group.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings.

In Figure 1, l is a meniscus plastic lens that makes up the first group, 2 is a plastic cemented lens that makes up the second group, 3 is a single glass lens that makes up the second group, and 4 is a plastic lens that makes up the third group. A concave lens, 5 a liquid for cooling the projection tube, and 6 a face plate of the projection tube.

The first lens group has an aspherical surface on the screen side, and corrects insufficient correction of the sagittal field curvature of the three groups, both of which have convex surfaces relative to the screen, suppresses the occurrence of sagittal flare, and improves the projection lens. Contributes to larger aperture and angle of view.

The second group is the main part of the present invention and consists of a plastic cemented lens 2 and a single glass lens 3, and has the maximum lens power of the lenses of the present invention. The plastic cemented lens 2 is made of PMMA (Polymethyl
It consists of a convex lens 2a made of polycarbonate (methacrylate) material and a concave lens 2b made of polycarbonate (PC) material. By forming the screen side surface of the convex lens 2a and the glass lens side surface of the concave lens 2b as aspherical surfaces, residual aberrations caused by the single glass lens 3 are corrected. Plastic has a temperature coefficient of refractive index and a coefficient of linear expansion that are about 100 times larger and about 10 times larger than glass, respectively, so it is difficult to use plastic for lenses with strong lens power. In consideration of this point, the single lens 3 having the main lens power of the second group is made of glass, thereby suppressing focal shift due to temperature changes.

The third group has the second lens power after the second group and corrects curvature.

Note that the aberration correction of the refractive projection lens of the present invention is performed using liquid 5.
Needless to say, this also takes into consideration the face plate 6.

Next, examples according to the present invention will be shown. Here, Tld,n,
ν represents the radius of curvature of each refractive surface, the center thickness and air gap of the lens, the refractive index for the e-line, and the Ashibe number for the d-line, and the subscript indicates the order of each from the object side.

In addition, the aspherical shape has a Z axis in the optical axis direction and a y axis perpendicular to the optical axis.
When we take the axis and let a1 to a be the aspherical coefficients, Z=a, y"+azV' + a3y' + aaV"
+asyI0.

FIG. 2 shows spherical aberration, astigmatism, and distortion corresponding to the example, FIG. 3 shows longitudinal chromatic aberration, and FIG. 4 shows the following:
It shows the amount of focus shift on the screen side due to temperature change when 20°C is the standard. Tables 1 and 2 respectively show the focal length of the entire system/focal length of each group, and the focal length of the second group/focal length of each lens of the second group, corresponding to the examples.

Synthetic focal length f = 100x*, angle of view 2ω =
556, F number = 1.1, shooting magnification 9.0xγ
, 127.77 d, 4
．． 5 go γ2 165.49 d,
115.53T3 64.59 d3
24.00r, -348,36d,
4.14γS 120.78 d, 0
．． 83r6 99.10 d6 15
．． 7277 -190.22 dt
61.38rs -50,73da
2.90T9 plane a, 8.
27rho plane dto 8
．． 52r++ Plane γr 73 a, -3,9434X10-3 7.740611a
2 3.6643X10-8 4.8811×1(a
36.3067X10"8.03'15X1fa
, -5,3145X10-16-1.8927Xl (a
s 6.3799X10-" 9.1939X1
(n, 1.492!It 5
8nz 1.492 ν2 58n,
, 1.589 ν3 29n,
1.591 ν4 61ns 1.
492 shi, 58n, 1.443 n7 1.540 )-34,1396x10-3-9.8526xlO-
3)"'6.7576X10-' 3.0
527X, 1O-6)-12-1,5671X10-”
7.2287X10-10)-154,9268
X10-"-3, 2794X10-")-"-4,
,5544X10-19-1.0576X10-” table
1 Table 2 (Effects of the Invention) As detailed above, the present invention comprises a refractive projection lens consisting of three groups of plastic lenses and glass lenses,
In particular, since the second group is composed of a plastic cemented lens and a single glass lens, it is possible to improve chromatic aberration and focus shift due to temperature changes, and it is also a high-performance, lightweight, and inexpensive refractive projection lens. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a refractive projection lens according to an embodiment of the present invention. FIGS. 2 and 3 are aberration curve diagrams corresponding to the examples, and FIG. 4 is the example Cq vs. 1--meniscus plastic lens, 2-----plastic cemented lens, 3--・・・・−Glass single lens, 4−−
−−−−−Plastic concave lens, 5...−? &Body, 6・−・−・・−Faceplate.

Claims (2)

[Claims] (1) From the screen side, the first group includes a meniscus lens with convex surfaces on both sides relative to the screen, the second group includes a plastic cemented lens and a single glass lens, and the third group includes a negative lens with a concave surface relative to the screen. A refractive projection lens comprising: (2) The screen-side surface of each of the meniscus lens, the plastic cemented lens, and the negative lens, and the surface of the plastic cemented lens on the glass single lens side are aspherical. 1
The refractive projection lens described in Section 1.