JP3066925B2 - Zoom lens - Google Patents

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 particularly to a zoom lens suitable for projection.

[0002]

2. Description of the Related Art First, FIG. 10 shows a configuration diagram of a projection television for projecting an image formed on a general color liquid crystal screen. 1 emits light collimated by a white light source. 2 is a liquid crystal display element, 3 is a reflection mirror, 4 , 5 , 6
Denotes a red reflecting dichroic mirror, a green reflecting dichroic mirror, a blue reflecting dichroic mirror, respectively, and 7 denotes a projection lens.

In such a configuration, since at least two mirrors such as a reflection mirror or a dichroic mirror need to be arranged between the final surface of the projection lens and the liquid crystal display element (between back focuses), the projection lens Requires a long back focus.

[0004]

By the way, a so-called two-group type lens having a long back focus, a lens having a negative refractive power as a simple zoom lens, and a lens having a positive refractive power next. Although a zoom lens is conceivable, for example, when this two-group type zoom lens is applied to a projection lens for high vision, which has a large image circle and severe demands on chromatic aberration of magnification, a problem arises in that chromatic aberration of magnification cannot be sufficiently corrected. I have.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a zoom lens which secures a relatively long back focus and has good optical performance with little chromatic aberration of magnification.

The feature of the present invention is that the first lens group having a negative refractive power and the second lens group having a positive refractive power are arranged in this order from the screen side. In a zoom lens that changes the focal length by changing the distance between the groups, the second lens group includes a front lens group on the screen side and a rear lens group on the original image side. The group includes a positive lens satisfying the following conditional expression.

[0007] θ _g . F2rP- (0.6438-0.001682νd
2rP)> 0.005 where θ _g . F2rP: anomalous dispersion value of the positive lens in the rear group of the second lens, νd2rP: Abbe number of the positive lens in the rear group of the second lens, θ _g . _{F = (n g -n F)} / (n F -n C), n g; g-line refractive index of n _F; refractive index of _{F-line n C; C-} line refractive index of The following simultaneously It satisfies the conditional expression. bf _W / f _W > 1.6 0.55 <| f ₁ / f ₂ | < 11 <| β _2W | <2 where bf _W : back focus at the wide end, f _w : whole system at the wide end F ₁ ; focal length of the first lens group ; f ₂ ; focal length of the second lens group; β _2W ; lateral magnification at the wide end of the second lens group

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A zoom lens according to the present invention will be described below with reference to the drawings. FIGS. 1, 4 and 7 are sectional views of a zoom lens according to the present invention. I is a first lens group having a negative refractive power, II is a second lens group having a positive refractive power, S is a screen, and a dichroic mirror (not shown) is provided to the right of the second lens group, and a liquid crystal. Etc. are arranged. Then, an image formed on the display element is transferred to a screen S via a zoom lens.
Projected to Zooming from the wide end to the tele end is performed by moving as shown by the arrow. Focusing is performed by moving the first lens group.
In the lens cross-sectional view, an asterisk (*) indicates an anomalous dispersion glass.

In the present embodiment, the second lens group is particularly composed of a front group IIf and a rear group IIr in order to provide an optical performance with little chromatic aberration of magnification and very high image quality even when applied to a projection zoom lens for high vision. Glass having anomalous dispersion is used for the positive lens in the rear group of the second lens in which the principal ray passes through a high position when divided.

At this time, it is desirable to satisfy the following conditions.

[0011] θ _g . F2rP− (0.6438−0.001682νd2rP)> 0.005 (1) where θ _g . F2rP: Indicates an abnormal dispersion value of the positive lens in the rear group of the second lens. νd2rP: indicates the Abbe number of the positive lens in the rear group of the second lens.

Here, θ _g . _{F = (n g -n F)} / (n F -n c) n g; refractive index of g-line, n _F; refractive index of F-line, n _c; the refractive index of C-line, νd2rP; first This is the Abbe number of the rear group of the two lenses.

As described above, in this embodiment, among the first lens group having a negative refractive power and the second lens group having a positive refractive power,
Glass having anomalous dispersion that satisfies the conditional expression (1) is used for the positive lens in the rear group of the second lens. Since the distance h from the optical axis to the principal ray of the off-axis light beam passing through the rear group of the second lens becomes large, the effect on the chromatic aberration of magnification is large, and if achromatization is performed with a combination of glasses having no anomalous dispersion, the g-line High-order aberrations in the lateral chromatic aberration of
In particular, if the value exceeds the range of the conditional expression, the chromatic aberration of magnification greatly exceeds the angle of view at the end of the angle of view. In order to suppress this, glass having anomalous dispersion is used for the positive lens in the rear group of the second lens.

In order to further correct this chromatic aberration of magnification, it is desirable that at least one negative lens satisfying the following conditional expression is provided in the rear group of the second lens.

[0015] θ _g . F2rn− (0.6438−0.001682νd2rn)> − 0.003 (2) where θ _g . F2rn: anomalous dispersion value of the second lens rear group negative lens, νd2rP: Abbe number of the second lens rear group negative lens.

On the other hand, the first lens group is separated from the first lens group by the largest air gap in the first lens group, and the first lens front group I on the screen side.
Configure than _f a first lens rear group of the original image side Ir, it is desirable to configure so as to satisfy the following condition to the first lens front group I _f.

Ν _1f > 55 (3) where ν _1f is the average value of Abbe numbers of the first front lens unit _If .

Conditional expression (3) is limited to the average value of the Abbe number of the front group of the first lens, and it becomes difficult to correct the chromatic aberration of magnification below the conditional expression.

Further, it is preferable to satisfy the following conditional expression.

Bf _W / f _W > 1.6 (4) 0.55 <| f ₁ / f ₂ | <1 (5) 1 < | β _2W | <2 (6) where bf _W Back focus at the wide end of the entire system, f _W ; focal length of the entire system at the wide end, f ₁ ; focal length of the first lens group, f ₂ ; focal length of the second lens group, β _2W ; Lateral magnification at wide end of group

Conditional expression (4) is a conditional expression which gives a sufficient back focus for disposing a color separation optical system such as a liquid crystal projector between the projection lens and the original image. The back focus cannot be obtained, or the focal length at the wide end becomes longer, and the projection magnification tends to decrease at a certain projection distance, which is not preferable.

Conditional expression (5) is a conditional expression relating to the ratio of the focal length of the second lens unit to the focal length of the first lens unit. If the lower limit value is exceeded, the focal length of the first lens unit becomes too short. The curvature becomes excessive, and it becomes difficult to correct coma.

On the other hand, if the value exceeds the upper limit, the focal length of the first lens unit becomes too long, and the amount of movement of the second lens unit during zooming becomes too large.

Condition (6) restricts the magnification of the second lens unit. If the lower limit value is exceeded, it becomes difficult to obtain a sufficient back focus or the total length at the wide end becomes undesirably long. .

On the other hand, when the value exceeds the upper limit, the focal length of the first lens group becomes extremely small, and it becomes difficult to correct aberrations such as curvature of field and coma. In addition, since the back focus is unnecessarily long, the overall length is undesirably increased.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the screen, Di is the i-th lens thickness and air gap in order from the object side, and Ni and νi are the i-th lenses in order from the object side.
The refractive index and Abbe number of the glass of the second lens. Each number
In the value examples, * indicates anomalous dispersion as in the lens cross-section.
Is the glass. In each numerical example,
Anomalous dispersion of two positive lenses and two negative lenses
Glass, but the two positive lenses are
The glass of the two negative lenses is the same material.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

As described above, in the two-unit zoom lens composed of the first lens unit having a negative refractive power and the second lens unit having a positive refractive power in this order from the screen side, the lens unit closest to the original image side By using glass having anomalous dispersion for the rear lens group, a zoom lens with relatively long back focus and low chromatic aberration of magnification was realized.

By reducing the chromatic aberration of magnification, a projection image with less color fringing can be obtained even when used for a projection lens for high vision, which requires extremely high image quality.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a first embodiment of the present invention.

FIG. 2 is an aberration diagram at a wide end according to the first embodiment of the present invention.

FIG. 3 is an aberration diagram at a telephoto end according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a lens according to a second embodiment of the present invention.

FIG. 5 is an aberration diagram at a wide-angle end according to a second embodiment of the present invention.

FIG. 6 is an aberration diagram at a telephoto end according to a second embodiment of the present invention.

FIG. 7 is a sectional view of a lens according to a third embodiment of the present invention.

FIG. 8 is an aberration diagram at a wide-angle end according to a third embodiment of the present invention.

FIG. 9 is an aberration diagram at a telephoto end according to a third embodiment of the present invention.

FIG. 10 is a sectional view of a conventional projector device.

[Explanation of symbols]

I 1st lens group II 2nd lens group _{If f} 1st lens front group Ir _r 1st lens rear group II _f 2nd lens front group II _r 2nd lens rear group

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (3)

(57) [Claims] A first lens group having a negative refractive power and a second lens group having a positive refractive power, in order from the screen side;
In a zoom lens that changes the focal length by changing the distance between the first lens group and the second lens group, the second lens group is located between the front lens group on the screen side and the rear lens group on the original image side. constructed, the during the second lens rear group Re <br/> includes positive lens at least one which satisfies the following condition Rutotomoni, theta _g. F2rP- (0.6438-0.001682νd2rP)>
0.005 where θ _g . F2rP; anomalous dispersion value of the positive lens of the second lens rear group, νd2rP; Abbe number of the positive lens of the second lens rear group, theta _{g. F = (n g -n F)} / (n F -n C), n g; g-line refractive index of n _{F; F-line} refractive index n _C of; and refractive index of C-line, the following conditions A zoom characterized by satisfying the formula
lens. bf _W / f _W > 1.6 0.55 <| f ₁ / f ₂ | < 11 <| β _2W | <2 where bf _W : back focus at the wide end, f _w : whole system at the wide end F ₁ ; focal length of the first lens group ; f ₂ ; focal length of the second lens group; β _2W ; lateral magnification at the wide end of the second lens group 2. The zoom lens according to claim 1, wherein the rear group of the second lens includes at least one negative lens satisfying the following conditional expression. θ _g . F2rn− (0.6438−0.001682νd2rn) <−
0.003 where θ _g . F2rn; anomalous dispersion value of the negative lens in the second lens rear group Nyudi2rn; Abbe number of the negative lens in the second lens rear group, 3. The first lens front group includes a first lens front group on the screen side and a first lens rear group on the original image side, and the first lens front group satisfies the following conditional expression. The zoom lens according to claim 1 or 2, wherein ν _1f > 55 where ν _1f ; average value of Abbe numbers of the lenses in the front group of the first lens.