JP2002122782A - Variable focal finite zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable focal finite zoom lens constituted, so that a large screen is obtained by a projecting lens for enlarging/projecting a DMD, a very bright projection screen is obtained with less distortions, and a high definition image may be obtained, even though the zoom lens is provided with power-varying function. SOLUTION: The zoom lens is constituted by arranging a 1st group, a 2nd group, a 3rd group and a 4th group, in this order from a screen side. In the case of varying the power between a wide-angle side and a telephoto side, the 2nd group, the 3rd group and the 4th group are moved in non-linear fashion. Each focal distance F1 to F4 up to the 1st to 4th groups and the total focal distance Fw at the wide-angle side satisfy prescribed conditions, and abnormal dispersion lenses are used for two or more lenses in the 2nd group and the rear group lens in the 4th group, and a low dispersion lens is used for the final lens of the front group in the 4th group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to digital video, particularly DMD, which must be adapted to the field of video in conjunction with digitization of information which has been rapidly developing in recent years.
(Varifocal finite zoom lens for enlarging and projecting (digital micromirror device)).

[0002]

2. Description of the Related Art Light, light and short are the trends of the times,
The situation in which images are transmitted on a large screen and information is enjoyed is also expanding. In the 21st century, it is expected that a movie system using a conventional film will be replaced with a digital light processing (DLP) system using a projection lens as in the present invention. Many projection lenses for liquid crystal projectors have already been provided on the market as projection lenses. However, since these projection lenses are still used for liquid crystal having a large number of pixels, not so high performance projection lenses are required. Further, it is impossible to make the screen very bright due to the heat resistance of the liquid crystal. Therefore, it is not possible to obtain a bright large screen with the current liquid crystal projection system. Also, the boundaries of the pixels are conspicuous on the screen, which is not preferable.

[0003]

SUMMARY OF THE INVENTION DL using DMD
The P-type projection device can eliminate the disadvantage of the liquid crystal projector. However, in comparison with the three-plate system, in principle, lens design becomes more difficult than a projection lens for a liquid crystal projector. Since the DMD is a reflection type device, the illumination light beam must be incident from the front side of the DMD. Therefore, a space in which a more complicated prism system enters the RGB three-color combining prism system is required between the projection lens and the DMD. Therefore, the projection lens has a very long lens back focus.

Taking a projection lens for a liquid crystal projector, which is currently mainstream, as an example, for a liquid crystal 1.3 ', the wide-side focal length is about 48 mm, and the lens back focus is at most about one time the focal length in air conversion. . Under such conditions, lens design is not so difficult. The present invention relates to a projection lens mounted on a DLP type projection apparatus, and there is a demand for a lens back focus that is about twice as long as the focal length on the wide side. This is also one indicator of the difficulty of lens design. Also, unlike liquid crystals, the pixels are small, and projection lenses are also required to have extremely high performance.

Since the projection lens is used in an interchangeable lens system, the focus point on the RGB axis must always be within a certain range even when zooming is performed. In addition, it is necessary to align the three pixels of RGB, and the chromatic aberration of magnification must be suppressed to within 1/2 pixel at most. Further, when the zoom area of the projection zoom lens shifts to the telephoto side, the focal length becomes relatively long and inevitably the axial chromatic aberration increases. However, as described above, since this projection zoom lens is used in an interchangeable lens system, axial chromatic aberration must be kept small even if the focal length shifts to the telephoto side. The present invention has been made in view of the above circumstances, and its purpose is to obtain a large screen,
Despite being a zoom lens with a zoom function,
An object of the present invention is to provide a variable focal finite zoom lens capable of obtaining a high-definition image with a very bright projection screen and little distortion.

[0006]

In order to achieve the above object, a varifocal finite zoom lens according to the present invention comprises:
A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power are arranged from the screen side. In the case of zooming from the wide side to the telephoto side, zooming can be performed by moving the second lens group, the third lens group, and the fourth lens group to the DMD side, and the zoom has no lens cemented surface. A lens, wherein the focal length of the first lens group is F1, the focal length of the second lens group is F2, the focal length of the third lens group is F3, the focal length of the fourth lens group is F4, and Assuming that the focal length on the wide side is Fw, 1.5 <F1 / Fw <3.6 (1) 1.5 <| F2 / Fw | <3.2 (2) 0.9 <F3 / Fw <2 ... (3) 0.5 <F4 / Fw <1.6 ... ( 4) The second lens group satisfies the following condition, and among the lenses having a negative refractive power, two or more lenses use Abbe number lenses satisfying the following condition: ν _d > 81 (5) and air space T5 between the sixth lens L ₆ of the fifth lens L ₅ and a convex meniscus lens of a double concave lens wherein the second lens group is an 0.3 <T5 / Fw <0.8 ··· (6) The fourth lens group is divided into a front group and a rear group, a relatively large air gap is provided between the front group and the rear group, and the rear lens group has a positive refractive power. Abbe number [nu _d of the convex lens is used the ν _d> 81 ··· (7) the condition of the lens, and the final lens L ₁₁ of the front group has a positive refractive power, its Abbe number [nu _d [nu _d > 70 (8)

According to the above configuration, the optical performance becomes high, and a zoom lens that projects images of image circles φ16 to φ20 and pixels of 14 μ class can be realized.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings. The zoom lens according to the present invention is DL
Applied to P projector optical system. The light reflected by the DMD enters the zoom lens via the projector optical system, is enlarged, and is projected on a screen. The optical system of a DLP projector has a feature that light use efficiency is higher than that of a liquid crystal that transmits light. Also, the back focus is larger than that of the liquid crystal type.

FIGS. 1A and 1B show an embodiment of a varifocal finite zoom lens according to the present invention. FIG. 1A shows a wide state, FIG. 1B shows a normal state, and FIG. First lens group 1 having positive refractive power
Is composed of a negative meniscus lens L _{1 having} a convex surface facing the screen side from the screen side, a biconvex lens L _2, and a positive meniscus lens L ₃ . The second lens group 2 having a negative refractive power includes a positive meniscus lens L ₄ having a convex surface facing the screen, a biconcave lens L ₅ , a convex lens L _6, and a negative meniscus lens L _{7 having} a convex surface facing the screen. it is, distance T5 between the biconcave lens L ₅ and the convex lens L ₆ has a relatively large air gap.

[0010] The third lens group 3 consists of a biconvex single lens L _8, the fourth lens group is composed of front and rear groups. Biconcave lens front group L ₉ and L ₁₀ and a biconvex lens L ₁₁
Contains. The rear group includes a negative lens L ₁₂ having a convex surface facing the screen side, a positive meniscus lens L ₁₃ having a convex surface facing the DMD side, a biconvex lens L _14, and a positive meniscus lens L ₁₅ having a convex surface facing the screen side. In. This is a four-group type zoom lens that can perform zooming by moving the second, third and fourth lens groups 2, 3 and 4 nonlinearly on the optical axis to the DMD side.

The focal length of the first lens unit 1 is F1, the focal length of the second lens unit 2 is F2, the focal length of the third lens unit 3 is F3, the focal length of the fourth lens unit 4 is F4, and the entire lens system. 1.5 <F1 / Fw <3.6 (1) 1.5 <| F2 / Fw | <3.2 (2) 9 <F3 / Fw <2 (3) 0.5 <F4 / Fw <1.6 (4)

In the above-mentioned conditional expression (1), the focal length F1 of the first lens unit 1 is smaller than the lower limit value 1.5 in the conditional expression (1).
If the above conditions are not satisfied, if the distortion is set to a predetermined value, the spherical aberration will be under on the wide side, and the periphery of the lens M will be under. Conversely, if the resolution is to be improved, the distortion will be undercorrected. If the entire power distribution is redone in the second and subsequent units, the required overall aberration balance cannot be obtained. Next, unless the focal length F1 of the first lens group 1 satisfies the upper limit value of 3.6 or less in the conditional expression (1), the entire power distribution becomes inappropriate.
In addition, the chromatic aberration of magnification is greatly increased to the side, and it becomes difficult to correct the chromatic aberration.

For the focal length F2 of the second lens group 2.
If F2 / Fw | does not satisfy the upper limit value of 3.2 or less in the conditional expression (2), the distortion is under, and the M
Is also unfavorable because the surrounding area is under. Further, in the second lens group 2, if the air interval T5 is relatively large and two or more lenses do not satisfy ν _d > 81 (5), distortion of the distortion is maintained while balancing other aberrations. Correction becomes difficult.

F with respect to the focal length F3 of the third lens group 3
If 3 / Fw does not satisfy the lower limit value of 0.9 or more of the conditional expression (3), the spherical aberration is under on the wide side and the spherical aberration is over on the tele side, so that the overall aberration balance is lost. F3 / Fw with respect to the focal length F3 of the third lens group 3
If the value of conditional expression (3) does not satisfy the upper limit value 2 or more of the conditional expression (3), the distortion becomes under on the wide side, which is not preferable.

F with respect to the focal length F4 of the fourth lens unit 4
4 / Fw is 0.5 <F4 / Fw <1.6 ...
If (4) is not satisfied, the distortion will be lost, and the overall aberration balance will be lost. If an arbitrary allowable range of aberration is slightly allowed from required performance, power distribution outside the above conditions can be performed. However, in practice, it is required to have a performance higher than the optical performance described later, so that it becomes difficult to correct aberration.

Next, as described above, since the zoom lens according to the present invention is mounted on a projection device compatible with the DLP type three-plate DMD, it is required to correct extremely small chromatic aberration of magnification and axial chromatic aberration. The air space T5 between the sixth lens L ₆ of the fifth lens L ₅ and a convex meniscus lens of the double-concave lens in the second lens group in order that 0.3 <T5
/Fw<0.8 (6), the fourth lens unit 4
Among the rear lens units, a lens with the condition of Abbe number ν _d > 81 (8) of a convex lens having a positive refractive power is used. And a lens of the Abbe number ν _d> 70 ··· (8) further to the final lens L ₁₁ having a positive refractive power of the front group.

Hereinafter, specific data examples will be shown. Note that 0
The face is a screen.

[Table 1]

[Table 2]

FIGS. 2A and 2B are diagrams showing spherical aberration, curvature of field, distortion and chromatic aberration of magnification in Table 1, wherein FIG. 2A shows a wide state, FIG. 2B shows a normal state, and FIG. For field curvature, each wavelength is 460 nm and 546 n
For m and 620 nm, a meridional image plane (solid line) and a sagittal image plane (dotted line) are shown. Distortion is for 546 nm. The same applies to FIG. 4 described later.

FIGS. 3A and 3B show a second embodiment of the present invention. FIG. 3A shows a wide state, FIG.
(C) shows the telephoto state, respectively. 4 group zoom 3
The configuration of the group moving type zoom lens is the same as that of the embodiment of FIG.

Hereinafter, specific data examples will be shown. Note that 0
The face is a screen.

[Table 3]

[Table 4]

FIGS. 4A and 4B are diagrams showing spherical aberration, curvature of field, distortion and chromatic aberration of magnification in Table 3, wherein FIG. 4A shows a wide state, FIG. 4B shows a normal state, and FIG.

[0022]

As described above, according to the present invention, a very bright, low-distortion, large-screen, high-quality DL
A projection image in the P projection device can be obtained. The zoom lens according to the present invention can realize extremely high-performance optical performance while maintaining a long back focus because the prism system for taking in the illumination light beam and the color separation prism system enter the rear side of the projection lens.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of a varifocal finite zoom lens according to the present invention, wherein FIG.
(B) shows a normal state, and (c) shows a tele state.

FIGS. 2A and 2B are diagrams showing spherical aberration, field curvature, distortion and chromatic aberration of magnification in Table 1, wherein FIG. 2A shows a wide state, FIG. 2B shows a normal state, and FIG.

FIGS. 3A and 3B are diagrams showing a second embodiment of the present invention, wherein FIG.
Shows a wide state, (b) shows a normal state, and (c) shows a tele state.

4A and 4B are diagrams showing spherical aberration, field curvature, distortion, and chromatic aberration of magnification in Table 3, wherein FIG. 4A shows a wide state, FIG. 4B shows a normal state, and FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1st lens group 2 ... 2nd lens group 3 ... 3rd lens group 4 ... 4th lens group 5 ... Prism system 6 ... DMD

Continued on the front page F term (reference) 2H087 KA06 KA07 PA15 PA17 PB15 QA02 QA06 QA17 QA21 QA25 QA32 QA41 QA45 RA32 RA41 RA42 SA23 SA27 SA29 SA32 SA63 SA64 SA65 SA72 SB04 SB15 SB22 SB31

Claims (1)

[Claims] (1) a first side having a positive refractive power from a screen side;
A lens group, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power are arranged, and the magnification is changed from the wide side to the telephoto side. In this case, zooming can be performed by moving the second lens group, the third lens group, and the fourth lens group to the DMD side, and there is no lens cemented surface, and the focus of the first lens group is When the distance is F1, the focal length of the second lens group is F2, the focal length of the third lens group is F3, the focal length of the fourth lens group is F4, and the focal length on the wide side of the entire lens system is Fw. .5 <F1 / Fw <3.6 (1) 1.5 <| F2 / Fw | <3.2 (2) 0.9 <F3 / Fw <2 (3) 0.5 <F4 / Fw <1.6 (4), and the second lens , Of the lens having a negative refractive power,
Two or more lenses use a lens having an Abbe number satisfying the following condition: ν _d > 81 (5), and the fifth lens L ₅ of the biconcave lens and the sixth lens L ₆ of the convex meniscus lens of the second lens group are used. The air gap T5 between the lens group is 0.3 <T5 / Fw <0.8 (6). The fourth lens group is divided into a front group and a rear group, and the fourth lens group is divided into a front group and a rear group. during a relatively provided a large air gap, among the lens groups the rear group, the Abbe number [nu _d of the convex lens having a positive refractive power using ν _d> 81 ··· (7) the condition of the lens, and final lens L ₁₁ of the front group has a positive refractive power, Vary focal finite zoom lens its Abbe number [nu _d, wherein ν _d> 70 ··· (8) becomes possible.