JP2001228398A - Zoom lens for projection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens for projection whose entire length is made shorter without lowering optical performance. SOLUTION: This zoom lens 5 is constituted of five groups, that is, a 1st lens group 10 to a 5th lens group 50 having negative, positive, positive, negative and positive refractive power in order from a screen side. The position of the 5th lens group 50 is fixed, and the 1st lens group 10 to the 4th lens group 40 are relatively moved on an optical axis at the time of variable power. By moving the 1st lens group 10 at the time of variable power, the fluctuation of aberration caused with the variable power is restrained, and the entire length of the lens need not be made long.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection zoom lens suitable for a projector for enlarging and projecting an image displayed on a film, a slide, or a liquid crystal display on a screen.

[0002]

2. Description of the Related Art In a projector for enlarging and projecting an image displayed on a film, a slide or a liquid crystal display on a screen, a telecentric type zoom lens is used as an optical system for projection. The projection zoom lens is designed to reduce image plane fluctuations during zooming.
The four-group type and the five-group type are the mainstream.

FIG. 10 shows a lens configuration of a conventional five-group type projection zoom lens. Zoom lens 8
0 denotes a first lens group 81 having a negative refractive power, a second lens group 82 having a positive refractive power, a third lens group 83 having a positive refractive power, and a fourth lens group having a negative refractive power, in order from the screen side. 84, a fifth lens group 85 having a positive refractive power. On the image plane side of the fifth lens group 85, a parallel glass 86 as a combining prism is arranged. The positions of the first lens group 81 and the fifth lens group 85 are fixed, and the second lens group 82, the third lens group 83, and the fourth lens group 84
Is relatively moved on the optical axis, so that the magnification is changed from the wide-angle end to the telephoto end.

[0004]

In order to increase the diameter of the zoom lens having the above-described configuration, it is necessary to suppress variations in various aberrations due to zooming, so that the total length of the lens must be increased. In a conventional zoom lens, in the case of a five-unit type, since the first lens unit is fixed at the time of zooming, shortening the entire length of the lens causes a decrease in optical performance. It is generally known that aberrations can be effectively corrected by forming a part of the lens surface of the constituent lens into an aspherical shape, but processing is difficult by making a lens with a large lens diameter aspherical. Cost increases. Even when this method is used, the chromatic aberration of magnification is increased and the curvature of the image plane is increased by shortening the overall length of the lens while increasing the aperture, thereby deteriorating the optical performance.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a projection zoom lens in which the overall length of the lens is reduced without lowering the optical performance.

[0006]

In order to achieve the above object, a zoom lens according to the present invention includes a zoom lens in order from a screen side.
A first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, and a fifth lens group having a positive refractive power. It consists of 5 groups,
When zooming from the wide-angle end to the telephoto end, the fifth lens group is fixed, and the first, second, third, and fourth lens groups are controlled by light. It is relatively moved on an axis.

The zoom lens according to claim 2 is
When zooming from the wide-angle end to the telephoto end, the first
The lens group is moved toward the image plane.

[0008]

According to the present invention, the zoom lens is formed in a five-group form, and the fifth lens group located closest to the image plane is fixed to maintain telecentricity during zooming. Further, at the time of zooming, by moving the first lens group together with the second, third, and fourth lens groups, fluctuations of various aberrations due to zooming can be suppressed, and the zoom lens at the telephoto side can be used. The overall length of the lens can be reduced. Also, since the aberration variation is reduced, the distortion can be easily corrected. Therefore, it is possible to reduce the number of positive lenses in the first lens group generally used for correcting the distortion, and to reduce the aberration on the wide-angle side. Can be shortened.

Further, by moving the first lens group from the screen side to the image plane side, the size at the time of telephoto and at the time of non-use is made compact.

[0010]

FIG. 1 shows a lens configuration of a projection zoom lens according to the present invention. Zoom lens 5
Are, in order from the screen side, a first lens group 10 having a negative refractive power, a second lens group 20 having a positive refractive power, a third lens group 30 having a positive refractive power, and a fourth lens group 40 having a negative refractive power. , A fifth lens group 50 having a positive refractive power. On the image plane side of the fifth lens group 50, a parallel glass 60 as a combining prism is arranged.

The fifth lens group 50 has a fixed position, and when performing zooming from the wide-angle end to the telephoto end, the first lens group 10, the second lens group 20, and the third lens group The lens group 30 and the fourth lens group 40 are relatively moved on the optical axis. At this time, the first lens group 10 is moved toward the image plane.

[0012]

[First Embodiment] Zoom lens 5 according to the first embodiment
Has substantially the same lens configuration as the conventional zoom lens 80 shown in FIG. The first lens group 10 includes, in order from the screen side, a positive lens 11, a negative lens 12, and a negative lens 13. The second lens group 20 includes two lenses, a positive lens 21 and a negative lens 22.

The third lens group 30 is composed of two lenses: a positive lens 31 having convex surfaces on both sides, and a meniscus-shaped negative lens 32 having a concave surface facing the screen. Positive lens 31
And the negative lens 32 are joined to form a compound lens.

The fourth lens group 40 is composed of a negative lens 41, a negative lens 42 having both concave surfaces, a positive lens 43 having both convex surfaces, and a positive lens 44. The negative lens 42 having both concave surfaces and the positive lens 43 having both convex surfaces are:
They are joined to form a compound lens. The fifth lens group 50 includes two positive lenses 51 and 52.

An aperture SP is provided between the third lens group 30 and the fourth lens group 40. During zooming, the stop SP is moved integrally with the fourth lens group 40.

In the zoom lens 5 of the first embodiment, the focal length f changes within a range of 37.16 mm to 48.30 mm.
The F-numbers Fno at the wide-angle end, the intermediate position, and the telephoto end are (1.73), (1.89), and (2.
03). Further, the total length L of the optical system from the first lens group 10 to the parallel glass 60 is 145.44 mm to 15
2.48 mm, and the total length L becomes shorter toward the telephoto side.

Table 1 below shows the lens data of the zoom lens 5. The surface number i is a number given to the surface of each lens in order from the screen side, and the surface interval D represents the lens thickness or air space between the next surface (unit is m).
m).

[0018]

[Table 1]

With the object distance set to infinity, the focal length f is set to 37.16 mm, 42.73 mm, and 48.30 mm.
, The surface distance D6 between the first lens group 10 and the second lens group 20, the surface distance D10 between the second lens group 20 and the third lens group 30, and the surface distance between the third lens group 30 and the stop SP D13 and the surface distance D21 between the fourth lens group 40 and the fifth lens group 50 change as shown in Table 2 below.

[0020]

[Table 2]

FIG. 2 is a diagram showing aberrations of the zoom lens 5 at the wide-angle end.
FIG. 3 shows aberration diagrams at the telephoto end. In each of FIGS. 2 and 3, (A) shows spherical aberration,
(B) represents astigmatism, and (C) represents distortion. Also,
Symbols C, d, and F in the spherical aberration diagram of (A) are C line (656.3 nm), d line (587.6 nm),
The astigmatism with respect to the F-line (486.1 nm) is shown, and the symbols S and T in the astigmatism diagram of (B) represent the aberration with respect to the spherical and meridional image planes, respectively.

[Second Embodiment] FIG. 4 shows a second embodiment of the zoom lens according to the present invention.
The zoom lens 5 shown in FIG. The zoom lens 6 of the second embodiment is obtained by removing the positive lens in the first lens group generally used for correcting distortion.

The first lens group 10 is composed of two lenses, a negative lens 12 and a negative lens 13, in this order from the screen side. The second lens group 20 includes a positive lens 21, a meniscus-shaped positive lens 23 having a convex surface facing the image surface side, and a meniscus-shaped negative lens 24 having a concave surface facing the screen side.
It is composed of two lenses. The positive lens 23 and the negative lens 24 are joined to form a compound lens.

The third lens group 30 is composed of a compound lens in which two lenses, a positive lens 31 and a negative lens 32, are cemented.

The fourth lens group 40 is composed of two lenses, a negative lens 41 and a positive lens 44. The fifth lens group 50 includes a negative lens 53 having concave surfaces on both sides, a positive lens 54 having convex surfaces on both sides, and two positive lenses 51 and 52. The negative lens 53 having concave surfaces on both sides and the positive lens 54 having convex surfaces on both sides are joined to form a compound lens.

In the zoom lens 6 of the second embodiment, the focal length f changes within a range of 37.96 mm to 45.54 mm.
The F-numbers Fno at the wide-angle end, the intermediate position, and the telephoto end are (1.75), (1.94), and (2.
05). The total length L of the optical system is 115.10.
mm to 123.07 mm. Table 3 below shows the lens data of the zoom lens 6.

[0027]

[Table 3]

When the object distance is infinity, the focal length f is 37.96 mm, 41.75 mm, 45.54 mm
In this case, the surface distance D4 between the first lens group 10 and the second lens group 20, the surface distance D9 between the second lens group 20 and the third lens group 30, the third lens group 30 and the fourth lens group 40, And the surface distance D16 between the fourth lens group 40 and the fifth lens group 50 change as shown in Table 4 below.

[0029]

[Table 4]

FIG. 5 is an aberration diagram at the wide-angle end of the zoom lens 6, and FIG. 6 is an aberration diagram at the telephoto end.

Comparative Example FIG. 7 shows a zoom lens adopting a conventional method in which the first lens group and the fifth lens group are fixed with substantially the same lens configuration as the zoom lens 6 of the second embodiment. Things. The reference numerals in the figure are used in common with the zoom lens 6 shown in FIG. In the zoom lens 7 of this comparative example, since the position of the first lens group 10 is fixed, the positive lens 1 for correcting distortion is provided in the first lens group 10.
1 is provided. The second lens group 20, the third lens group 30, the fourth lens group 40, and the fifth lens group 50 have the same lens configuration as the zoom lens 6 of the second embodiment shown in FIG.

In the zoom lens 7 of this comparative example, the focal length f changes within a range of 36.64 mm to 43.96 mm.
The F-numbers Fno at the wide-angle end, the intermediate position, and the telephoto end are (1.77), (1.92), and (2.
06). The total length L of the optical system is 127.86 m
m, and the total lens length is longer than that of the zoom lens 6 that moves the first lens group 10. Table 5 below shows the lens data of the zoom lens 7.

[0033]

[Table 5]

With the object distance at infinity, the focal length f is 36.64 mm, 40.30 mm, 43.96 mm
In this case, the surface distance D6 between the first lens group 10 and the second lens group 20, the surface distance D11 between the second lens group 20 and the third lens group 30, the surface distance D11 between the third lens group 30 and the fourth lens group 40, And the surface distance D18 between the fourth lens group 40 and the fifth lens group 50 vary as shown in Table 6 below.

[0035]

[Table 6]

FIG. 8 is an aberration diagram at the wide-angle end of the zoom lens 7, and FIG. 9 is an aberration diagram at the telephoto end.

[0037]

As described above, according to the present invention, the zoom lens is formed in a five-group form, and the fifth lens group located closest to the image plane is fixed. Can be maintained. Also, at the time of zooming, the first lens group, the second lens group, the third lens group,
By moving the lens group relatively on the optical axis, fluctuations of various aberrations due to zooming are reduced as compared with a conventional zoom lens in which the position of the first lens group is fixed, and the zoom lens on the telephoto side. The overall length of the lens can be reduced. In addition, since the aberration variation is reduced, the distortion can be easily corrected.
The positive lens in the first lens group, which is generally used for correcting distortion, can be omitted, and the overall length of the lens on the wide-angle side can be reduced.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram showing a first embodiment of a zoom lens according to the present invention.

2A and 2B are aberration diagrams at the wide-angle end of the zoom lens shown in FIG. 1, wherein FIG. 2A shows spherical aberration, FIG. 2B shows astigmatism, and FIG. 2C shows distortion.

3A and 3B are aberration diagrams at the telephoto end of the zoom lens shown in FIG. 1, where FIG. 3A shows spherical aberration, FIG. 3B shows astigmatism, and FIG. 3C shows distortion.

FIG. 4 is a lens configuration diagram showing a second embodiment of the zoom lens according to the present invention.

5A and 5B are aberration diagrams at the wide-angle end of the zoom lens shown in FIG. 4, in which FIG. 5A shows spherical aberration, FIG. 5B shows astigmatism, and FIG. 5C shows distortion.

6A and 6B are aberration diagrams at the telephoto end of the zoom lens shown in FIG. 4, in which FIG. 6A shows spherical aberration, FIG. 6B shows astigmatism, and FIG. 6C shows distortion.

FIG. 7 is a lens configuration diagram showing a conventional zoom lens system of a variable magnification system.

8A and 8B are aberration diagrams at the wide-angle end of the zoom lens shown in FIG. 7, in which FIG. 8A shows spherical aberration, FIG. 8B shows astigmatism, and FIG. 8C shows distortion.

9A and 9B are aberration diagrams at the telephoto end of the zoom lens shown in FIG. 7, in which FIG. 9A shows spherical aberration, FIG. 9B shows astigmatism, and FIG. 9C shows distortion.

FIG. 10 is a lens configuration diagram showing a conventional five-group type zoom lens.

[Explanation of symbols]

 5, 6, 7, 80 Zoom lens 10, 81 First lens group 20, 82 Second lens group 30, 83 Third lens group 40, 84 Fourth lens group 50, 85 Fifth lens group 60, 86 Parallel glass

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H087 KA06 NA02 PA10 PA11 PA19 PB13 QA02 QA06 QA07 QA12 QA17 QA22 QA25 QA26 QA32 QA34 QA41 QA45 RA36 RA41 SA44 SA46 SA49 SA53 SA55 SA62 SA63 SA64 SA65 SA76 SB03 SB04 SB13 SB13 SB43 SB45

Claims (2)

[Claims] A first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, The fifth lens unit is configured as a fifth lens unit having a positive refractive power, and when performing zooming from the wide-angle end to the telephoto end, the fifth lens unit is fixed, and the first lens unit, A projection zoom lens, wherein the second lens group, the third lens group, and the fourth lens group are relatively moved on the optical axis. 2. The projection system according to claim 1, wherein the first lens group is moved toward an image plane when zooming from the wide-angle end to the telephoto end. Zoom lens.