JPH11202200A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized zoom lens which has excellent optical performance and also has the reduction-side pupil position fixed during power variation and is sufficiently telephotographic and suitable to a projection type display device. SOLUTION: The zoom lens is equipped with a 1st lens group G1 with negative refracting power, a 2nd lens group G2 with positive refracting power, a 3rd lens group G3 with negative refracting power, and a 4th lens group G3 with positive refracting power in order from the enlargement side and is varied in power by moving the 2nd lens group G2 and 3rd lens group G2 along the optical axis while the 1st lens group G1 and 4th lens group G4 are fixed. In this case, a condition 0.45<|d1|/fw<1 is met, where f1 is the focal length of the 1st lens group G1 and fw is the focal length of the whole lens system in the wide-angle state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to a projection zoom lens which is almost telecentric on the reduction side used in a projection type display device using a transmission type liquid crystal display device or a reflection type liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal projection display device has the advantages that the device is simpler and smaller than the CRT projection display device. For this reason, in recent years, there has been an increasing demand for a liquid crystal projection display device instead of a conventional CRT projection display device.

[0003]

A projection display device using a liquid crystal display device is different from a projection display device of a self-luminous type such as a CRT system in that a liquid crystal display device is formed by using an illumination light source and an illumination optical system. The image is projected by lighting. In order to obtain a color image, first, the illumination light is separated into three primary colors of red, green, and blue by a color separation / synthesis means such as a dichroic prism, and each color light is modulated by a liquid crystal display device. Then, the modulated color lights are combined again by the color separating / combining means, and then projected by the projection optical system. Therefore, since a color separating / combining means exists between the liquid crystal display device and the projection optical system, the projection optical system for the projection display device using the liquid crystal display device needs a long back focus.

Further, in order to prevent color shading due to the angular dependence of the spectral characteristics of the color separation / synthesis means, it is necessary that the entrance pupil is sufficiently far, that is, an optical system which is telecentric on the reduction side. . For this reason,
As a projection zoom lens for a projection display device using a liquid crystal display device, a positive, negative, positive, and positive four-group type zoom lens frequently used for telephoto and TV is used.

However, in recent years, it has been desired to increase the angle of view of the projection optical system. In a conventional four-group type zoom lens of positive, negative, positive, and positive, the positive first group becomes very large, and a wide image is formed. Keratinization is difficult and problematic. In addition, the negative and positive two-group type zoom lens can relatively easily widen the angle of view,
The pupil position on the reduction side cannot be set far enough. In addition, since the pupil position changes due to zooming, it is not suitable for a projection optical system for a projection type display device using a liquid crystal display device, which is a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a small size, good optical performance, a pupil position on the reduction side fixed during zooming, and a sufficiently long projection type display. It is an object to provide a zoom lens suitable for an apparatus.

[0007]

In order to achieve the above object, according to the present invention, a first lens group Gl having a negative refractive power and a second lens group having a positive refractive power are arranged in order from the magnification side. G2 and a third lens group G3 having negative refractive power
And a fourth lens group G4 having a positive refractive power. The second lens group G2 and the third lens group G3 are moved along the optical axis to perform zooming, and the first lens group G1 And the fourth lens group G4 is a zoom lens which is fixed during zooming, where f1 is the focal length of the first lens group G1 and fw is the focal length of the entire lens system at the wide-angle end. | F1 | / fw <1 (1)

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of the above-described zoom lens of the present invention will be described. The zoom lens in each embodiment projects an image displayed on a spatial light modulation element such as a liquid crystal display device on a screen (not shown) at an enlargement magnification, and sequentially from the enlargement side (the long conjugate length side, That is, in order from the screen side), the first lens group G1 has a negative refractive power, and its position is fixed during zooming. The second lens group G2 has a positive refractive power, and the third lens group G3 has a negative refractive power. The second lens group G3 moves along the optical axis to correct magnification and change in image position due to magnification. It is carried out. The fourth lens group G4 has a positive refractive power and is fixed with respect to the image plane during zooming.

Under such a configuration, in order to provide a projection zoom lens having a small lens diameter on the enlargement side and excellent optical performance, the following conditional expression (1): 0.45 <| f1 | / fw < 1 (1) is preferably satisfied. Here, f1 represents the focal length of the first lens group G1, and fw represents the focal length of the entire zoom lens system in the wide-angle end state.

Conditional expression (1) is an expression that defines conditions for obtaining good optical performance while reducing the lens diameter on the enlargement side. If the lower limit of conditional expression (1) is exceeded, the negative refracting power of the first lens group G1 becomes strong, the Petzval sum of the entire lens system increases negatively, and it is difficult to maintain the flatness of the image plane. Become. Conversely, when the value exceeds the upper limit of conditional expression (1), the entrance pupil position becomes distant, and the height of the principal ray passing through the lens surface on the enlargement side increases, so that the lens diameter on the enlargement side increases. The optical system becomes large.

In the present invention, it is preferable that the following conditional expression (2) is satisfied: 0.5 <f2 / fw <0.75 (2) Here, f2 represents the focal length of the second lens group G2.

Conditional expression (2) is an expression that defines conditions for obtaining good imaging performance in the entire zoom range. When the value goes below the lower limit of conditional expression (2), fluctuations of various aberrations due to zooming become large, and it becomes difficult to perform satisfactory aberration correction over the entire zooming range. Conversely, if the value exceeds the upper limit of conditional expression (2), the amount of movement of the second lens unit G2 during zooming becomes large, which undesirably leads to an increase in the size of the entire lens system.

The fourth lens unit G4 is fixed during zooming. The fourth lens unit G4F having a negative refractive power and the fourth lens unit G4R having a positive refractive power are arranged in order from the magnification side.
have. With this configuration, a long back focus can be ensured, and the pupil position on the reduction side is fixed during zooming, and can be made sufficiently far (ie, almost telecentric).

In the present invention, it is preferable that the following conditional expression (3) is satisfied: 0.6 <| f4F | / f4 <2.5 (3) Here, f4 represents the focal length of the fourth lens group G4, and f4F represents the focal length of the front group G4F in the fourth lens group G4.

Conditional expression (3) is to make the entrance pupil sufficiently distant,
It is an equation that defines conditions for obtaining good imaging performance. When falling below a lower limit value of conditional expression (3), the fourth lens unit G
4, the negative refractive power of the front group G4F becomes stronger than necessary,
The Petzval sum of the entire lens system increases negatively, and it is difficult to maintain the flatness of the image plane, which is not preferable. vice versa,
When the value exceeds the upper limit of conditional expression (3), it becomes difficult to prevent color shading due to the angular dependence of the spectral characteristics of the dichroic prism and the like.

In the present invention, it is desirable that the following conditional expression (4) is satisfied: 0.7 <| f4F | / f4R <3 (4) Here, f4R represents the focal length of the rear group G4R in the fourth lens group G4.

Conditional expression (4) is an expression that defines conditions for obtaining good imaging performance while securing a long back focus. When the value goes below the lower limit of conditional expression (4), the fourth condition is satisfied.
The negative refractive power of the front group G4F in the lens group G4 becomes unnecessarily strong, and the Petzval sum of the entire lens system increases negatively, which makes it difficult to maintain the flatness of the image plane, which is not preferable. Conversely, when the value exceeds the upper limit of conditional expression (4), it becomes difficult to secure a sufficiently long back focus.

In the present invention, it is preferable to move the first lens group G1 along the optical axis for focusing.

[0019]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In each of the following first to third embodiments, in order from the magnification side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens having a negative refractive power A group G3 and a fourth lens group G4 having a positive refractive power, wherein the second lens group G2 and the third lens group G3 are moved along the optical axis to perform zooming; The lens group G1 and the fourth lens group G4 are fixed during zooming. The stop is provided between the third lens group G3 and the fourth lens group G4, and is fixed together with the fourth lens group G4.

(First Embodiment) FIG. 1 is a diagram showing a configuration of a zoom lens according to a first embodiment. In order from the enlargement side, a negative meniscus lens having a convex surface facing the enlargement side, a biconvex lens, a negative meniscus lens having a convex surface facing the enlargement side, a first lens group G1 composed of a biconcave lens, and a negative lens having a convex surface facing the enlargement side. A second lens group G2 composed of a cemented lens of a meniscus lens and a biconvex lens and a biconvex lens; a third lens group G3 composed of a cemented lens of a biconcave lens and a positive meniscus lens having a convex surface facing the enlargement side; A fourth lens front group G4F including a positive meniscus lens having a convex surface and a negative meniscus lens having a convex surface facing the reduction side, a cemented lens of a biconcave lens and a biconvex lens, and a positive meniscus lens having a convex surface facing the reduction side. And a fourth lens group G4 having a fourth lens rear group G4R formed of a biconvex lens. Focusing is performed by moving the first lens group G1 along the optical axis.

Table 1 below summarizes the data values of the first embodiment. In the table of the embodiment, f represents the focal length of the entire lens system when d0 = ∞, β represents the projection magnification, and Fno represents the F number. The surface number is the number of the lens surface counted from the enlargement side, r is the radius of curvature of the lens surface, d is the distance between the lens surfaces, and n is the e-line (λ =
546 nm) and ν represents the Abbe number. Such reference numerals are the same in all the following embodiments.

[0022]

[Table 1] f = 51.6 to 67.1 Fno = 3.5 Surface number r d v n d0 1.000000 1 116.2024 3.0000 50.84 1.661522 2 43.0382 5.0000 1.000000 3 247.3512 5.5000 60.64 1.605482 4 -95.5785 0.5000 1.000000 5 141.5084 3.0000 50.84 1.661522 6. 25.35 1.812674 16 28.6997 d3 1.000000 17 (Aperture) 4.0000 1.000000 18 -72.7210 5.0000 47.10 1.626888 19 -23.7609 3.0000 1.000000 20 -19.6437 2.5000 33.89 1.809452 21 -57.2814 26.5000 1.000000 22 -214.7139 3.0000 25.35 1.812674 23 93.5291 14.0000 64.10 1.518723 24 -58.6 25 -734.5506 8.0000 64.10 1.518723 26 -91.8118 0.5000 1.000000 27 139.0829 12.5000 64.10 1.518723 28 -92.5919 10.0087 1.000000 29 0.0000 45.0000 64.10 1.518723 30 0.0000 15.5000 1.000000 31 0.0000 39.0000 25.35 1.812674 32 0.0000 4.8000 1.000000 33 0.0000 3.2000 64.10 1.518723 34 0.0000 d4 1.000000 β -0.01290 -0.01471 -0.01678 d0 3948.0019 3948.0019 3948.0019 d1 10.24213 7.06232 4.28692 d2 2.40249 7.89183 14.10697 d3 9.81967 7.51097 4.070 (1) | f1 | /fw=0.736 (2) f2 / fw = 0.620 (3) | f4F | /f4=2.123 (4) | f4F | /f4R=2.304

FIGS. 2 to 4 show d0 in the first embodiment.
3A and 3B show various aberration diagrams in the wide-angle end state, at the intermediate focal length state (f = 58.85), and at the telephoto end, respectively. In each aberration diagram, FNO represents the F number, Y represents the image height, e represents the e-line (λ = 546 nm), and g represents the g-line (λ = 436n).
m). Such reference numerals are the same in various aberration diagrams of all the embodiments below. In addition, various aberration diagrams of all the embodiments including this embodiment show aberrations when a parallel plate such as a PBS is present in the optical system. As is clear from the figure, it can be seen that various aberrations are satisfactorily corrected.

(Second Embodiment) FIG. 5 is a diagram showing a configuration of a zoom lens according to a second embodiment. In order from the enlargement side, a negative meniscus lens having a convex surface facing the enlargement side, a biconvex lens, a negative meniscus lens having a convex surface facing the enlargement side, a first lens group G1 composed of a biconcave lens, a biconvex lens, and a convex surface on the enlargement side. A second lens group G2 composed of a cemented lens of a negative meniscus lens and a biconvex lens directed toward the lens, a second lens group G2 composed of a biconcave lens, and a third lens group G3 composed of a cemented lens of a biconcave lens and a positive meniscus lens having a convex surface facing the enlargement side A front group G4F including a positive meniscus lens having a convex surface facing the reduction side and a biconcave lens, a positive meniscus lens having a convex surface facing the reduction side, a cemented lens of a biconcave lens and a biconvex lens, and a rear group G4R including a biconvex lens. And a fourth lens group G4 having: In the present embodiment, focusing is performed by moving the first lens group G1 along the optical axis.

Table 2 below shows data values of the second embodiment of the present invention.

[0026]

[Table 2] f = 51.6 to 67.1 Fno = 3.5 Surface number rd ν nd0 1.000000 1 122.3095 3.0000 58.50 1.654256 2 48.8873 5.0000 1.000000 3 309.5413 7.0000 38.03 1.607183 4 -73.1132 0.5000 1.000000 5 163.7901 3.0000 58.50 1.654256 6 57.7942 8.0000 1.000000 7 -36.5308 3.0000 58.50 1.654256 8 161.1098 d1 1,000000 9 92.9587 8.0000 56.41 1.503487 10 -72.1021 0.5000 1.000000 11 74.1046 2.5000 25.35 1.812674 12 34.4210 11.0000 64.10 1.518723 13 -93.7858 0.5000 1.000000 14 48.7523 8.0000 56.41 1.487 1.000000 16 -96.9691 2.5000 64.10 1.518723 17 22.2641 4.0000 25.35 1.812674 18 32.6970 d3 1.000000 19 (Aperture) 5.5000 1.000000 20 -548.0455 5.0000 48.97 1.534303 21 -28.2817 3.0000 1.000000 22 -22.5222 2.5000 50.84 1.661522 23 86.8320 21.8753 1.000000 24 -231.059723. -45.5072 0.5000 1.000000 26 -254.9428 3.0000 25.35 1.812674 27 101.7165 14.0000 64.10 1.518723 28 -69.8656 0.5000 1.000000 29 131.2492 14.0000 64.10 1.518723 30 -82.8 220 10.0087 1.000000 31 0.0000 45.0000 64.10 1.518723 32 0.0000 15.5000 1.000000 33 0.0000 39.0000 25.35 1.812674 34 0.0000 4.80000 1.000000 35 0.0000 3.2000 64.10 1.518723 36 0.0000 d4 1.000000 β -0.01290 -0.01471 -0.01678 d0 3947.0000 3947.0000 3947.0000 d1 12.21423 8.4151092 209. 8.12973 6.78229 4.08412 d4 1.97062 1.97063 1.97062 (Conditional value) (1) | f1 | /fw=0.678 (2) f2 / fw = 0.630 (3) | f4F | /f4=0.883 (4) | f4F | /f4R=1.126

FIGS. 6 to 8 are graphs showing various aberrations in the wide angle end state when d0 = 3948, various aberration diagrams in the intermediate focal length state (f = 58.85), and a telephoto end in the second embodiment. FIG. As is clear from the figure, it can be seen that various aberrations are satisfactorily corrected.

(Third Embodiment) FIG. 9 is a diagram showing a configuration of a zoom lens according to a third embodiment. A first lens group G1 including, in order from the enlargement side, a negative meniscus lens having a convex surface facing the enlargement side, a positive meniscus lens having a convex surface facing the reduction side, a negative meniscus lens having a convex surface facing the enlargement side, and a biconcave lens; A second lens group G2 comprising a cemented lens of a negative meniscus lens having a convex surface facing the enlargement side and a biconvex lens, a second lens group G2 comprising a biconvex lens, and a third lens comprising a cemented lens of a biconcave lens and a positive meniscus lens having a convex surface facing the enlargement side. Lens group G
3, a front group G4F including a biconvex lens and a biconcave lens,
A positive meniscus lens with a convex surface facing the reduction side, a cemented lens of a biconvex lens and a negative meniscus lens with a convex surface facing the reduction side, and a convex surface facing the enlargement side arranged on the reduction side with the optical block interposed. And a fourth lens group G4 having a rear group G4R made of a plano-convex lens. In the present embodiment, focusing is performed by moving the first lens group G1 along the optical axis.

Table 3 below summarizes the data values of the third embodiment of the present invention.

[0030]

[Table 3] f = 51.6 to 67.1 Fno = 3.5 Surface number rd ν nd0 1.000000 1 78.3163 2.0000 50.84 1.661522 2 43.6977 4.5000 1.000000 3 -3817.6663 4.0000 60.64 1.605482 4 -103.9794 0.2000 1.000000 5 124.1547 2.0000 50.84 1.661522 6 44.5844 5.0000 1.000000 7 -128.8156 2.0000 50.84 1.661522 8 70.5871 d1 1,000 000 9 58.4677 2.0000 25.35 1.812674 10 37.7132 9.0000 57.03 1.625404 11 -80.0550 0.2000 1.000000 12 41.8362 6.0000 57.03 1.625404 13 -506.5514 d2 1.000000 15 -82.1386 1.5000 56.41 3.5000 27.61 1.761660 16 30.5727 d3 1.000000 17 (Aperture) 8.0000 1.000000 18 205.7016 4.5000 38.03 1.607183 19 -23.5214 1.5000 1.000000 20 -20.2071 1.5000 50.84 1.661552 21 74.7764 21.3449 1.000000 22 -4704.6400 9.5000 64.10 1.518723 23 -33.2800 0.2000 1.000000 24 74.7357 11.0000 24. -45.2844 2.0000 25.35 1.812674 26 -406.8021 10.0234 1.000000 27 0.0000 45.0000 64.10 1.518723 28 0.0000 2.5000 1.000000 29 90.0000 6.0000 64.10 1.518723 30 0.0000 7 .0000 1.000000 31 0.0000 39.0000 25.35 1.812674 32 0.0000 4.8000 1.000000 33 0.0000 3.2000 64.10 1.518723 34 0.0000 1.9837 1.000000 β -0.01290 -0.01471 -0.01678 d0 3950.0019 3950.0019 3950.0019 d1 11.32865 8.15714 5.39147 d2 4.33039 9.80461 15.99192 d3 9.56415 7.2698 3.813741 (Corresponding value) (1) | f1 | /fw=0.736 (2) f2 / fw = 0.620 (3) | f4F | /f4=1.426 (4) | f4F | /f4R=1.721

FIGS. 10 to 12 are graphs showing various aberrations at the wide-angle end when d0 = 3948, various aberrations at the intermediate focal length state (f = 58.85), and a graph at the telephoto end in the third embodiment. FIG. As is clear from the figure, it can be seen that various aberrations are satisfactorily corrected.

[0032]

As described above, according to the present invention,
It is possible to provide a zoom lens which is small, has good optical performance, the pupil position on the reduction side is fixed during zooming, and is sufficiently far away, which is suitable for a projection display device.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of a first embodiment of the present invention.

FIG. 2 is a diagram illustrating various aberrations of the first example in a wide-angle end state.

FIG. 3 shows an intermediate focal length state (f = 58.8) of the first embodiment.
It is a figure which shows various aberrations in 5).

FIG. 4 is a diagram showing various aberrations of the first embodiment in a telephoto end state.

FIG. 5 is a lens configuration diagram of a second embodiment of the present invention.

FIG. 6 is a diagram illustrating various aberrations of the second example in a wide-angle end state.

FIG. 7 shows an intermediate focal length state (f = 58.8) of the second embodiment.
It is a figure which shows various aberrations in 5).

FIG. 8 is a diagram illustrating various aberrations of the second example in a telephoto end state.

FIG. 9 is a lens configuration diagram of a third embodiment of the present invention.

FIG. 10 is a diagram illustrating various aberrations of the third example in a wide-angle end state.

FIG. 11 shows an intermediate focal length state (f = 58.
FIG. 85 is a diagram illustrating various aberrations in (85).

FIG. 12 is a diagram showing various aberrations of the third embodiment in a telephoto end state.

[Description of sign]

 G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group G4R Fourth lens front group G4F Fourth lens rear group S Aperture

Claims (4)

[Claims] 1. A first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power in order from the enlargement side.
And a third lens group G3 having a negative refractive power and a fourth lens group G4 having a positive refractive power. The second lens group G2 and the third lens group G3 are moved along the optical axis. The 1st lens group G
1 and the fourth lens group G4 are fixed during zooming, and the focal length of the first lens group G1 is f
1. The focal length of the entire lens system in the wide-angle end state is fw
Wherein: 0.45 <| f1 | / fw <1 (1) 2. The focal length of the second lens group G2 is set to f2.
The zoom lens according to claim 1, wherein the following condition is satisfied: 0.5 <f2 / fw <0.75 (2). 3. The fourth lens group G4 includes a fourth front lens group G4F having a negative refractive power and a fourth rear lens group G4R having a positive refractive power, in order from the magnification side. When the focal length of the fourth lens group G4 is f4, the focal length of the fourth front lens group G4F is f4F, and the focal length of the fourth lens rear group G4R is f4R, 0.6 <| f4F | / f4 < 3. The zoom lens according to claim 1, wherein the following condition is satisfied: 2.8 (3) 0.7 <| f4F | / f4R <3 (4). 4. The zoom lens according to claim 1, wherein the first lens group G1 is moved along an optical axis for focusing.