JPH04348308A - Projection lens - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection lens in a projection device such as a liquid crystal projector.

0002

2. Description of the Related Art Conventionally, a projection lens used in a liquid crystal projector has a fixed focal length, as shown in FIG.
It consists of, in order from the left side (screen side not shown), a plano-convex lens 1 with a convex surface facing left, a biconcave lens 2, an aperture 3, a biconcave lens 4, a biconvex lens 5, and a plano-convex lens 6 with a convex surface facing left. A glass plate 7 for a liquid crystal display element is arranged behind the convex lens 6 (on the right side). Such a projection lens condenses light from a liquid crystal display element (not shown) through a glass plate 7 with a plano-convex lens 6, a biconvex lens 5, and a biconcave lens 4, and narrows the condensed light with an aperture 3. , a biconcave lens 2 and a plano-convex lens 1 are used to project the image onto a screen (not shown) on the left side.

0003

[Problems to be Solved by the Invention] However, although the above-mentioned projection lens is composed of five lenses and therefore has a simple structure and is inexpensive, it has a low ability to correct astigmatism.
As the astigmatic difference increases and the sagittal and meridional image planes separate, image sharpness is lost, and there are drawbacks such as only a narrow angle of view can be obtained to obtain uniform image quality over the entire screen. . It should be noted that if the number of lenses is increased to about 7, high performance can be provided over a wide angle of view, but there is a problem that the price becomes extremely high due to the large number of lenses.

An object of the present invention is to provide a projection lens that can obtain uniform image quality over a wide angle of view with a small number of lenses.

[0005]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides, in order from the screen side, a meniscus convex lens with a convex surface facing the screen side, a meniscus concave lens with a convex surface facing the screen side, and a meniscus concave lens with a convex surface facing the screen side. A meniscus concave lens with its concave surface facing the screen side, a meniscus convex lens with its concave surface facing the screen side, and a plano-convex lens with its convex surface facing the screen side are arranged, and the refractive index of the i-th lens from the screen side is ni, and the first lens from the screen side. The focal length of the partial system by the second lens is f1~2, the third lens and 4.
When the focal length of the partial system using the second lens is f3 to 4, and the focal length of each lens is fi, (a) 1.6<n1, n4<1.72 (b) 1.65<n2, n3 <1.85(c)0.4<
f3~4/f1~2<2.5(d)-1.7<f2/f
It is characterized by satisfying the following conditions: 1<-1 (e)-1.8<f3/f4<-0.9.

[0006]

[Operation] The operation of the means of the present invention is as follows. Condition (a) concerns the refractive index of the first and fourth lenses; if the refractive index is smaller than 1.6, the astigmatism difference will increase and the homogeneity of the image will decrease, and if it is larger than 1.72, it will be expensive. Become something. Condition (b) concerns the refractive index of the second and third lenses; if the refractive index is smaller than 1.65, correction of off-axis aberrations will be insufficient, and image quality at the periphery of the image will deteriorate; If the size is too large, suitable materials may not be available and it will be expensive. Condition (c) is 1,
Regarding power sharing between the second lens subsystem and the third and fourth lens subsystems, if the conditions are not met, the symmetry of the subsystems will collapse and off-axis aberrations will be insufficiently corrected. Condition (d) relates to the power ratio of the first and second lenses; when it is smaller than -1.7, astigmatism at the intermediate angle of view becomes large, and when it is larger than -1, spherical aberration becomes large. Condition (e) concerns the power ratio of the third and fourth lenses, and if it is less than -1.8, it becomes 2.
The radius of curvature of the second lens becomes smaller and the workability deteriorates, and if it is larger than -0.9, it causes an increase in distortion and an increase in astigmatism at an intermediate angle of view. Therefore, by satisfying each of the above-mentioned conditions, the meniscus convex lens 2
With a small number of lenses, ie, two concave meniscus lenses and one plano-convex lens, it is possible to match the sagittal image plane and the meridional image plane, and it is possible to obtain uniform image quality over a wide angle of view.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 shows the configuration of a projection lens for a liquid crystal projector. This projection lens consists of a screen on the left (not shown) and a glass plate 10 for a liquid crystal display element on the right.
It is placed between That is, the projection lens includes, in order from the left side (screen side), a meniscus convex lens 11 with a convex surface facing the left side, a meniscus concave lens 12 with a convex surface facing the left side, an aperture 13, a meniscus concave lens 14 with a concave surface facing the left side, and a concave meniscus lens 14 with a concave surface facing the left side. The structure includes a meniscus convex lens 15 with its convex surface facing toward the left side, and a plano-convex lens 16 with its convex surface facing toward the left side. In this case, a partial system of the first meniscus convex lens 11 and a second meniscus concave lens 12 and a partial system of the third meniscus concave lens 14 and the fourth meniscus convex lens 15 are separated by the aperture 13. It is constructed almost symmetrically. In addition, the plano-convex lens 16
A glass plate 10 is placed on the right side of the screen.

In addition, the projection lens has a refractive index of the i-th lens from the left as ni, a focal length of the partial system made up of the first and second lenses 11 and 12 from the left as f1-2, and the third lens as ni. When the focal length of the partial system consisting of the fourth lenses 14 and 15 is f3 to 4, and the focal length of each lens is fi, (a
)1.6<n1, n4<1.72 (b) 1.65<n2, n3<1.85 (c) 0.4<
f3~4/f1~2<2.5(d)-1.7<f2/f
The configuration satisfies the following conditions: 1<-1 (e)-1.8<f3/f4<-0.9.

Each of the conditions (a) to (e) will be explained below. Condition (a) is the first meniscus convex lens 11
and the refractive index of the fourth meniscus convex lens 15. If the refractive index of each lens 11, 15 is smaller than 1.6, the astigmatism difference will increase and the homogeneity of the image will decrease. Conversely, if the refractive index of each lens 11, 15 is greater than 1.72, the material of the lens becomes expensive. Condition (b) relates to the refractive index of the second meniscus concave lens 12 and the third meniscus concave lens 14. The refractive index of each lens 12 and 14 is 1.6
If it is smaller than 5, correction of off-axis aberrations will be insufficient and the image quality in the periphery of the image will deteriorate. Conversely, if the refractive index of each lens 12, 14 is 1
．． If it is larger than 85, there is no suitable material and it becomes expensive. Condition (c) is for the first and second lenses 11 and 12.
, and the third and fourth lenses 14 and 15, respectively. If you deviate from this condition,
The first and second lenses 11 and 1 bordering on the aperture 13
The symmetry between the second partial system and the third and fourth lenses 14 and 15 is lost, resulting in insufficient correction of off-axis aberrations. Condition (d) relates to the power ratio of the first and second lenses 11 and 12. When the power ratio (f2/f1) is smaller than -1.7, astigmatism at the intermediate angle of view becomes large, and conversely, when it is larger than -1, spherical aberration becomes large. Condition (e) relates to the power ratio of the third and fourth lenses 14 and 15. When the power ratio (f3/f4) is smaller than -1.8, the radius of curvature of the second lens 12 becomes small, resulting in poor workability. On the other hand, if it is larger than -0.9, distortion increases and astigmatism at intermediate angles of view increases.

As described above, the projection lens described above is composed of two meniscus convex lenses 11 and 15, two meniscus concave lenses 12 and 14, and one plano-convex lens 16, so the number of lenses is five. It is possible to obtain a product with a simple structure, low cost, and the above-mentioned (a).
By satisfying each of the conditions (e), it is possible to match the sagittal image plane and the meridional image plane, and it is possible to obtain homogeneous image quality over a wide angle of view.

Next, Table 1 shows specific examples of the above-mentioned projection lens.
Shown below.

[Table 1] The conditions in Table 1 are: f=55.9mm, FNO=5.0
(at infinity), the object distance is 470 mm, and the image circle is 68φmm. Note that Ri represents the radius of curvature of each lens surface, di represents the center thickness of each lens or air space, ni represents the refractive index of each lens, and νi represents the Abbe number. As is clear from Table 1, the refractive index of the first and fourth meniscus convex lenses 11 and 15 is 1.640, which satisfies the condition (a), and the second and third meniscus concave lenses 12 , 14 has a refractive index of 1.847, which satisfies the condition (b). Furthermore, the radii of curvature of the first and fourth convex meniscus lenses 11 and 15 and the radii of curvature of the second and third concave meniscus lenses 12 and 14 are almost equal in absolute value, and The partial system of the eye and the partial systems of the third and fourth sheets are symmetrical, and the condition (c) is satisfied. Therefore, Table 1
The aberration performance of the projection lens in is a spherical aberration curve as shown in FIG. 2(A), an astigmatism curve as shown in FIG. 2(B), a distortion curve as shown in FIG. 2(C), It can be seen that the aberration performance is excellent. Furthermore, the MTF (Modulation Transfer Function) characteristics of the image plane at each point P1, P2, P3, and P4 in FIG. 1 are as shown in FIGS. 3(A) to (D).
15 lines/mm from the center of the image (P1) to the periphery of the image (P
It can be seen that between 4), the defocus-contrast curves are almost equal, the focus is consistent, and the curvature of the field is small. Therefore, the homogeneity of the image can be improved over a wide angle of view, and a high-quality, large-screen projected image can be obtained at short distances.

Note that the above-described embodiments are applicable not only to the projection lens of a liquid crystal projector, but also to projection devices such as films, handwritten transparent manuscripts, and cathode ray tubes.

[0013]

[Effects of the Invention] As explained above, according to the present invention, since it is composed of five lenses: two meniscus convex lenses, two meniscus concave lenses, and one plano-convex lens,
The structure is simple, the number of lenses is small, it can be obtained at low cost, and the configuration satisfies conditions (a) to (e), so it is possible to match the sagittal image plane and the meridional image plane. It is possible to obtain uniform image quality over a wide angle of view.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a projection lens.

[Figure 2] (a) is a spherical aberration diagram, (b) is an astigmatism diagram, (
c) is a distortion diagram.

FIG. 3 is an MTF characteristic diagram at points P1 to P4 in FIG. 1.

FIG. 4 is a configuration diagram of a conventional projection lens.

[Explanation of symbols]

11 Meniscus convex lens 12 Meniscus concave lens 14 Meniscus concave lens 15 Meniscus convex lens 16 Plano-convex lens

Claims (1)

[Claims] 1. In order from the screen side, a meniscus convex lens with a convex surface facing the screen side, a meniscus concave lens with a convex surface facing the screen side, a meniscus concave lens with a concave surface facing the screen side, a meniscus convex lens with a concave surface facing the screen side, A plano-convex lens with a convex surface facing the screen side is arranged, the refractive index of the i-th lens from the screen side is ni, and the focal length of the partial system consisting of the first and second lenses from the screen side is f1~2,3 When the focal length of the partial system consisting of the 4th and 4th lenses is f3 to 4, and the focal length of each lens is fi, (a) 1.6<n1, n4<1.72 (b) 1.65 <n2, n3<1.85(c)0.4<
f3~4/f1~2<2.5(d)-1.7<f2/f
1<-1 (e) A projection lens that satisfies the following conditions: -1.8<f3/f4<-0.9.