JPH0527174A - Zoom lens for finite distance - Google Patents

Abstract

PURPOSE:To provide the compact zoom lens which is made sufficiently large in field angle at a short-focus end suitably as the projection lens for a liquid crystal projector. CONSTITUTION:The zoom lens consists of a 1st positive lens group which moves only in focusing, a 2nd negative lens group which moves only in power variation, a 3rd negative lens group which moves so as to correct the position of an image plane varying in the power variation, and a 4th positive lens group which is fixed in both the focusing and power variation in order from an enlargement side. The 3rd lens group consists of one negative single lens and the 4th lens group consists of a front group composed of at least two positive single lenses and one negative single lens and a rear group composed of at least one positive single lens and one cemented lens and satisfies fB>1.6fw and f1<2.0fw. Here, fB is the back focus of the whole system, fw is the focal length of the whole system at the short-focus end, and f1 is the focal length of the 1st lens group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finite distance zoom lens suitable for liquid crystal projectors and the like.

[0002]

2. Description of the Related Art In recent years, various audiovisual devices are increasingly used in conferences and lectures. As a projection optical device used in such a case, a slide projector, an overhead projector, and the like are in widespread use.

On the other hand, recently, a television projector for projecting a CRT image and a liquid crystal projector for projecting a liquid crystal panel have appeared, and demand for household use is expected.

Projection inspection devices are widely used for industrial purposes.

Among these projection optical systems, the liquid crystal projector lens has a fixed focal length and a variable focal length.

In the case of a fixed focal length, it is necessary to change the projection distance by moving the screen or the projection apparatus main body when changing the projection magnification.

Further, even with a variable focal length, the angle of view at the short focal length end is small, so that it may not be possible to project a desired size when the size of the room is limited.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a compact zoom lens for a finite distance, which has a sufficiently large angle of view at the short focal point and is suitable as a projection lens for a liquid crystal projector.

[0009]

A zoom lens for a finite distance according to the present invention, which achieves the above object, comprises, in order from the enlargement side, a first lens unit having a positive refracting power and moving only during focusing, and having a negative refracting power during zooming. The second lens group that moves only, the third lens group that has a negative refractive power and moves to correct the image plane position that fluctuates during zooming, and the positive lens that has a positive refractive power and is fixed during focusing and zooming. The third lens group includes one negative single lens, and the fourth lens group includes at least two positive single lenses.
A zoom lens for a finite distance, characterized by comprising a front lens group consisting of a negative single lens element, a rear lens group consisting of at least one positive single lens element and one cemented lens element, and further satisfying the following expression.

F _B > 1.6 f _W ... f _l <2.0 f _W ... However, f _B : Back focus of the whole system f _W : Focal length of the short focus end of the whole system f _l : First lens group Focal length In addition to the above configuration and features, the first lens group is composed of a negative single lens and two positive single lenses in order from the magnification side, and the second lens group is composed of two negative single lenses in order from the magnification side. It is preferably composed of a positive single lens and a negative single lens.

[0011]

The zoom lens for a finite distance according to the present invention has the above-described structure, and as the zoom lens, the projection magnification can be freely changed while keeping the projection distance constant, and the installation of the projection device becomes very simple.

If the back focus becomes too short below the lower limit of the equation, it becomes difficult to install a dichroic mirror and an optical path bending mirror necessary for combining information from the liquid crystal panels of RGB colors in the optical path.

If the focal length of the first lens unit becomes too long beyond the upper limit of the formula, the moving amount of the first lens unit for focusing becomes large, so that the total lens length,
The total ball diameter also becomes large. Not only is the compactness impaired, but the cost is also high.

[0014]

EXAMPLES Examples of the present invention will be described below as Examples 1, 2, and 3.
Shown by.

Each of Examples 1, 2, and 3 has a lens structure shown in the sectional view of FIG.

Symbols in the table are as follows: r: radius of curvature of each refracting surface d: distance between each refracting surface n: refractive index of d line of lens material ν: Abbe number of lens material f: focal length ω of all diameters : Half angle of view m: Enlargement magnification f _l : Focal length of the first lens group f _W : Focal length at the short focal end of the entire system A, B, C: Shows the intervals between the lens groups.

(Example 1) F _NO = 4.5 f = 100.0 to 200.0 ω = 25.2 ° to 12.2 ° m = 30.3 to 14.7 rd n ν 1 386.653 3.00 1.80518 25.4 2 100.731 4.00 3 111.830 10.60 1.60311 60.7 -4 -203.170 0.20 5 55.608 7.50 1.62299 58.2 6 115.416 A 7 89.761 2.00 1.77250 49.6 8 30.921 7.00 -9 -327.413 1.80 1.72000 50.2 10 62.480 1.00 11 47.594 6.70 1.80518 25.4 12 -304.602 2.50 13 -61.145 1.70 1.77250 49.6 14 -342.433 570 1.6385.49 1.49 16 -114.292 C 17 -272.027 4.00 1.75520 27.5 18 -68.815 2.50 19 51.047 5.00 1.65844 50.9 20 -908.557 2.35 21 -148.962 4.00 1.75520 27.5 22 58.744 17.30 23 488.875 8.00 1.51823 59.0 24 -75.524 0.20 25 200.755 2.00 1.80518 25.426 13.721 7.70 61.2 27 -159.036 group interval f a B C 100.0 5.12 27.17 8.22 136.0 19.71 12.59 8.21 200.0 35.54 3.45 1.53 f B / f W = 1.65 f l / f W = 1.12 Figure 2, Figure 3, the aberration of Figure 4 example 1 Fig. 2 shows the short focus, Fig. 3 the middle focus. FIG. 4 is an aberration diagram at the long focal end.

(Example 2) F _NO = 4.5 f = 100.0 to 189.9 ω = 24.2 ° to 12.0 ° m = 30.3 to 15.7 rd n ν 1 331.018 2.84 1.80518 25.4 2 92.789 3.78 3 94.122 10.03 1.60311 60.7 4 -353.030 0.19 5 79.763 7.09 1.62299 58.2 6 667.844 A 7 2080.342 1.89 1.77250 49.6 8 46.295 8.70 9 -491.045 1.70 1.71300 53.9 10 46.825 0.95 11 46.825 6.34 1.80518 25.4 12 -288.516 1.23 13 -94.122 15 15 16 -122.974 C 17 ∞ 3.78 1.75520 27.5 18 -61.941 3.78 19 135.158 3.12 1.65844 50.9 20 -265.813 2.22 21 -52.801 6.43 1.75520 27.5 22 274.431 22.04 23 -567.478 5.86 1.51633 64.1 24 -59.151 0.19 25 401.832 1.89 1.80518 25.4 26 90.096 7.28 1.589 61.2 27 -107.839 group interval f a B C 100.0 4.57 26.03 7.49 146.0 22.56 8.98 6.55 189.9 33.43 3.51 1.16 f B / f W = 1.87 f l / f W = 1.10 5, 6, aberrations 7 example 2 Fig. 5 shows the short focus end, and Fig. 6 the middle focus position. Figure 7 is an aberration diagram at the long focal end.

Example 3 F _NO = 4,5 f = 100.0 to 189.5 ω = 24.0 ° to 11.9 ° m = 30.3 to 15.7 r d n ν 1 349.616 2.88 1.80518 25.4 2 96.211 3.77 3 99.088 10.00 1.60311 60.7 4- 307.295 0.19 5 78.831 7.08 1.62299 58.2 6 573.063 A 7 976.308 1.89 1.77250 49.6 8 44.405 8.68 9 -356.086 1.70 1.72000 50.2 10 47.025 0.94 11 46.812 6.32 1.80518 25.4 12 -264.610 1.23 13 -89.124 1.60 1.77250 49.6 14 -403.834. 1.63854 55.4 16 -122.647 C 17 ∞ 3.77 1.75520 27.5 18 -65.802 3.77 19 115.336 3.11 1.65844 50.9 20 -281.922 2.22 21 -55.954 6.42 1.75520 27.5 22 238.659 21.98 23 -338.321 5.85 1.51823 59.0 24 -58.229 0.19 25 358.954 1.89 1.80518 25.4 26 88.043 7.27 1.58913 61.2 27 -107.600 group interval f A B C 100.0 4.83 25.64 7.66 132.8 18.60 11.88 7.65 189.5 33.53 3.26 1.34 f B / f W = 1.86 f l / f W = 1.09 8, 9 and 10 example 3 FIGS. 8A and 8B are aberration charts of FIG. 10 is an aberration diagram at the long focal end.

[0020]

As is clear from the examples and various aberration diagrams, the finite distance zoom lens of the present invention has a variable power ratio of about 2 and each aberration is well corrected.

By using the zoom lens for finite distance of the present invention, the projection magnification can be changed without moving the screen and the main body of the projection apparatus, and the installation for projecting an image in a desired size becomes easy.

Further, since the angle of view at the short focus end is made sufficiently large, it is possible to project a desired size even in a general room size.

The finite distance zoom lens of the present invention is suitable not only as a projection lens for a liquid crystal projector but also as various projection lenses.

[Brief description of drawings]

FIG. 1 is a sectional view showing a lens structure of the present invention.

FIG. 2 is an aberration diagram for Example 1 at a short focal length end.

FIG. 3 is an aberration diagram at a mid-focal position of Example 1.

FIG. 4 is an aberration diagram at the long focal length end of Example 1;

FIG. 5 is an aberration diagram for Example 2 at the short focus end.

FIG. 6 is an aberration diagram for Example 2 at a middle focal point position.

FIG. 7 is an aberration diagram at a long focal length end of Example 2;

FIG. 8 is an aberration diagram for Example 3 at the short focus end.

FIG. 9 is an aberration diagram at a middle focal position of Example 3.

FIG. 10 is an aberration diagram at a long focal length end of Example 3;

Claims (2)

[Claims] 1. A first lens group having a positive refracting power and moving only during focusing in order from the enlargement side, a second lens group having a negative refracting power and moving only during zooming, and a zooming lens having a negative refracting power The third lens group is composed of a third lens group that moves to correct the image plane position that fluctuates from time to time, and a fourth lens group that has a positive refractive power and is fixed during focusing and during zooming. The fourth lens group includes one front lens, and the fourth lens group includes a front group including at least two positive single lenses and one negative single lens, and a rear group including at least one positive single lens and one cemented lens. And a zoom lens for a finite distance characterized by satisfying the following formula. f _B > 1.6 f _W f _l <2.0 f _W However, f _B : Back focus of the whole system f _W : Focal length of the short focal end of the whole system f _l : Focal length of the first lens group 2. The first lens group is composed of a negative single lens and two positive single lenses in order from the magnification side, and the second lens group is composed of two negative single lenses, positive single lenses and negative lenses in order from the magnification side. The zoom lens for finite distance according to claim 1, which is composed of a single lens.