JPH07120676A - Zoom lens - Google Patents

Abstract

PURPOSE:To form a zoom lens for projecting a liquid crystal display image to be a telecentric structure in order to reduce the shading resulted from a liquid indicator, and provide a satisfactory image. CONSTITUTION:The zoom lens is formed out of a first lens group 11 having positive refracting power, a second lens group 12 having negative refracting power, a third lens group 13 having positive refracting power, and a fourth lens group 14 having positive refracting power in order from the large conjugation side. At power variation from short focus end to long focus end, the groups are moved on the optical axis in such a manner that the air space between the first lens group 11 and the second lens group 12 is increased, and the air space between the second lens group 12 and the third lens group 13 is reduced, and when the back focus in the case where the conjugation point on the large conjugation side is assumed to be infinity, is bfs, the focus distance of the whole system at the short focus end is fs, and the focus distance of the fourth group is f4, conditions of 0<=bfs/fs<0.3 and 1<f4/fs<3 are satisfied.

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 projection lens suitable for projecting an image.

[0002]

2. Description of the Related Art In recent years, a projector for projecting a video image alone or superposed on a screen has been widely used. A cathode ray tube, a liquid crystal display panel, or the like is used as an image display, but in the case of a liquid crystal display panel, an illumination optical system is required.

FIG. 17 schematically shows a liquid crystal projector. 1, 2, 3 are liquid crystal display panels corresponding to respective primary colors, 4, 5, 6 are condenser lenses, and light sources are provided close to the liquid crystal display panel. It is located on the 7 side. Reference numerals 8a to 8c are illumination light distribution mirrors, and 8d to 8f are image combining mirrors. A projection lens 9 has a light source image formed at the pupil position of the lens. In this figure, a parabolic mirror is arranged behind the light source 7, but a condenser lens may be arranged in front of the light source.

[0004]

On the other hand, when a liquid crystal display panel with a microlens array for improving aperture efficiency is used as the liquid crystal display panel as shown in FIG. When the angle of the illumination light incident on the display panel deviates from the vertical direction (telecentric is broken), vignetting occurs as shown in FIG. 19 and the peripheral portion of the screen of the liquid crystal display panel becomes dark. An object of the present invention is to provide a zoom lens having good image performance, and a subordinate object to provide a zoom lens that can obtain an image in which a decrease in brightness is reduced when used in a projection system.

[0005]

SUMMARY OF THE INVENTION The present invention is a telecentric lens having a large lens group having positive refracting power on the conjugate side followed by a plurality of movable lens groups, and further including a lens group having smaller positive conjugate power on the conjugate side. A zoom lens with good properties was constructed.
However, it is desirable that the lens unit having a small positive refractive power on the conjugate side is fixed, and the lens unit may be a single lens.

The first lens unit having a positive refractive power, the second lens unit having a negative refractive power, and the third lens unit having a positive refractive power are arranged in this order from the large conjugate side.
The second lens unit includes a lens unit and a fourth lens unit having a positive refracting power, and when zooming from the short focus end to the long focus end, the air gap between the first lens unit and the second lens unit increases, Third
A zoom lens having good telecentricity is realized by moving each lens group on the optical axis so that the air gap of the lens group is reduced and satisfying one or more of the following conditional expressions, more preferably both.

0 ≦ bf _s / f _s <0.3 (1) 1 <f ₄ / f _s <3 (2) where bf _s is the back focus when the conjugate point on the large conjugate side is infinity. f ₄ : focal length of the fourth lens group f _s : focal length of the entire system at the short focal end

On the other hand, the first lens group having a positive refractive power, the second lens group having a negative refractive power, the third lens group having a positive refractive power, and the fourth lens group having a positive refractive power are arranged in order from the large conjugate side. The optical axis is configured to increase the air distance between the first lens group and the second lens group and decrease the air distance between the second lens group and the third lens group during zooming from the short focus end to the long focus end. By moving up and satisfying the following conditional expression,
A zoom lens with good telecentricity can be realized.

0.15 <D _23s / D _34s <0.6 (3) where D _{23s is} the air gap between the second lens unit and the third lens unit at the short focus end D _{34s is} the first air gap at the short focus end Air gap between 3rd lens group and 4th lens group Furthermore, it is desirable to satisfy the following conditional expressions.

0.5 <f ₁ / f _s <1.5 (4) 0.2 <-f ₂ / f _s <0.5 (5) 0.4 <f ₃ / f _s <1. 3 (6) where f ₁ : focal length of the first lens group f ₂ : focal length of the second lens group f ₃ : focal length of the third lens group Furthermore, it is desirable to satisfy the following conditional expression. .

0.16 <N _2p −N _2n <0.3 (7) where N _2p : average value of refractive index of the positive lens in the second lens group N _2n : negative lens in the second lens group Further, the third lens group is composed of a third front lens group on the large conjugate side and a third rear lens group on the small conjugate side with the largest air space in the third lens group. It is desirable that the following conditional expression be satisfied.

0.03 <D _3ab / f ₃ <0.2 (8) where D _3ab is the air gap between the 3a-th lens group and the 3b-th lens group, and the second lens group is arranged in order from the large conjugate side. , A negative lens having a strong power on the small conjugate side, a negative lens having a convex convex bonding surface toward the large conjugate side, and a positive lens having a strong power on the large conjugate side.

Furthermore, it is desirable that a fixed diaphragm that is fixed with respect to a small conjugate point is arranged between the third lens group and the fourth lens group.

Further, it is desirable that the fourth lens group be composed of one positive single lens and satisfy the following conditional expression.

-3.1 <SF ₄ <−0.3 (9) where SF ₄ = (r _4f + r _4r ) / (r _4f −r _4r ) r _4f : of the positive single lens of the fourth lens group. Large radius of curvature on conjugate side r _4r : Radius of curvature on small conjugate side of positive single lens of the fourth lens group

[0016]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 illustrate lens cross-sectional shapes sequentially corresponding to Numerical Examples 1 to 4 described later.

Reference numeral 10 indicates a screen. The first lens group 11 is located on the large conjugate side and has a positive refractive power, and
In order from the smaller conjugate side, 12 is a movable second lens group having a negative refractive power, 13 is a movable third lens group having a positive refractive power, and the front group 13a and the rear group are separated by the largest distance in this group. Divided into group 13b. sp ′ is a diaphragm that moves integrally with the third lens group, and sp is a fixed diaphragm. Reference numeral 14 denotes a fourth lens unit having a fixed and positive refracting power, and in this example, it is composed of a positive lens having a strong convex surface directed toward the large conjugate side. Third lens group 13
There is the largest space between the fourth lens group 14 and the fourth lens group 14 in which the synthetic mirror system of FIG. 17 is arranged, and 15 is a liquid crystal display panel provided with microlenses. Further, when the magnification is changed from the short focal end S to the long focal end L, it moves according to the movement locus shown by the solid line of the arrow.

The fourth lens group 14 is arranged near a small conjugate point and satisfies the above conditional expression (1) or / and (2).

When the magnification is changed from the short focus end to the long focus end, the second lens group is moved to the small conjugate side, and the third lens group is moved to the large conjugate side, thereby changing the magnification. , The third lens group is distributed to obtain a large zoom ratio with a small amount of movement.

The meanings of the extreme values in the above conditional expressions will be summarized below.

Conditional expression (1) limits the ratio of the back focus and the focal length of the entire system at the short focal end when the conjugate point on the large conjugate side is infinity, and the lower limit of conditional expression (1) is set. In the area exceeding the above range, the liquid crystal display panel 15 and the fourth lens group 14 collide with each other, and in the area exceeding the upper limit value of the conditional expression (1), the width of the light flux in the fourth lens group 14 becomes wide, so that coma aberration and astigmatic difference occur. It is not preferable because the correction is difficult.

Conditional expression (2) limits the ratio of the focal lengths of the fourth lens group 14 and the entire system at the short focal point, and is preferable because the telecentricity is greatly broken outside the range of the conditional expression (2). Absent.

Conditional expression (3) is defined by the second lens group 1 at the short focal end.
The ratio of the air distance between the second lens group 13 and the third lens group 13 and the air distance between the third lens group 13 and the fourth lens group 14 at the short focus end is limited. In a region where the magnification ratio cannot be large and exceeds the upper limit of conditional expression (3), the magnification ratio can be large or the lens becomes large, or the air gap between the third lens group 13 and the fourth lens group 14 is large. It is not preferable because it becomes too small and it becomes difficult to insert a color combining system or the like between the third lens group 13 and the fourth lens group 14.

Conditional expression (4) limits the ratio of the focal length of the first lens group 11 to the focal length of the entire system at the short focal point, and the first lens is used in the region where the lower limit of conditional expression (4) is exceeded. Since the focal length of the group 11 becomes too short, it becomes difficult to correct axial chromatic aberration and spherical aberration of the entire system, and the total length becomes too large in a region exceeding the upper limit of conditional expression (4), which is not preferable.

Conditional expression (5) limits the ratio of the focal length of the second lens group 12 to the focal length of the entire system at the short focal length end. Since the negative power of the lens group becomes too strong, the curvature of field becomes over, and the distortion aberration at the short focal end becomes under, so that the negative power of the second lens group is exceeded in the region exceeding the upper limit of conditional expression (5). Since the power becomes too weak, the field curvature becomes under, and the amount of movement of the second lens group for obtaining a predetermined zoom ratio becomes large, which is not preferable.

Conditional expression (6) limits the ratio of the focal length of the third lens group 13 to the focal length of the entire system at the short focal end, and the third lens is used in the region where the lower limit of conditional expression (6) is exceeded. Since the focal length of the lens group 13 becomes too small, the air gap between the third lens group 13 and the fourth lens group 14 cannot be made large, and therefore, a color synthesizing system or the like is provided between the third lens group 13 and the fourth lens group 14. In the region exceeding the upper limit of conditional expression (6), the focal length of the third lens group becomes too large, so the conjugate point problem of the third lens group becomes too large, and therefore the total lens length becomes large. It is not preferable because it becomes too much.

Conditional expression (7) limits the difference between the average value of the refractive index of the positive lens in the second lens group 12 and the average value of the refractive index of the negative lens in the second lens group 12, and the conditional expression (7) The field curvature is over in a region exceeding the lower limit of (7), the field curvature is under in a region exceeding the upper limit of the conditional expression (7), and the distortion aberration at the short focal end is under. Absent. The under curvature of field that occurs in the fourth lens group is corrected by increasing the refractive index of the positive lens of the second lens group and decreasing the refractive index of the negative lens of the second lens group.

Conditional expression (8) is defined by the air gap between the third front lens group 13a and the third rear lens group 13b and the third lens group 13:
The focal length ratio of is limited by the conditional expression (8)
In a region exceeding the lower limit value of, the coma aberration becomes difficult to correct because the distance between the third lens unit and the third lens unit becomes too small, and in a region exceeding the upper limit value of the conditional expression (8), Since the total length becomes large, the lens becomes large, which is not preferable.

Further, in order to reduce the fluctuation of the distortion aberration generated at the time of zooming, the second lens group 12 is a negative lens having a strong power on the small conjugate side in order from the large conjugate side.
It is composed of a cemented negative lens with the convex surface of the cemented surface facing the large conjugate side, and a positive lens having a strong power toward the large conjugated side.

Conditional expression (9) limits the lens shape of the positive single lens of the fourth lens group 14, and in a region where the lower limit value of conditional expression (9) is exceeded, distortion aberration at the short focal point end is overcorrected. In a region exceeding the upper limit value of the conditional expression (9), distortion aberration at the short focus end becomes under, which is not preferable.

Further, in order to reduce the flare of off-axis light at the long focal length end, a fixed diaphragm fixed to a small conjugate point is arranged near the third lens group between the third lens group and the fourth lens group. is doing.

Numerical examples will be shown below.

Ri is the i-th radius of curvature from the large conjugate side di is the i-th lens surface distance from the large conjugate side ni is the refractive index of the i-th glass from the large conjugate side v i is the i-th glass from the large conjugate side Abbe number

[0034]

[Outer 1]

[0035]

[Outside 2]

[0036]

[Outside 3]

[0037]

[Outside 4] Aberrations at the short focus end, the middle focus, and the long focus end of Numerical Example 1 are shown in order in FIGS. 5, 6, and 7. Similarly, various aberrations of Numerical Example 2 are shown in FIGS. 8, 9 and 10, various aberrations of Numerical Example 3 are shown in FIGS. 11, 12 and 13, and various aberrations of Numerical Example 4 are shown. This is shown in FIGS. 14, 15 and 16, respectively.

[0038]

According to the present invention, a zoom lens having a high zoom ratio and a small size and excellent telecentricity can be realized, and particularly when it is used as a projection lens, it is effective for realizing a bright projector with good image quality.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view showing a first embodiment of the present invention.

FIG. 2 is a lens cross-sectional view showing a second embodiment.

FIG. 3 is a lens cross-sectional view showing a third embodiment.

FIG. 4 is a lens cross-sectional view showing a fourth embodiment.

FIG. 5 is a short focus aberration curve diagram of Numerical Example 1.

6 is an intermediate aberration curve diagram of Numerical Example 1. FIG.

FIG. 7 is a long focus aberration curve diagram of Numerical Example 1.

FIG. 8 is a short-and-long focus aberration curve diagram of Numerical Example 2.

9 is an intermediate aberration curve diagram of Numerical Example 2. FIG.

FIG. 10 is a long focus aberration curve diagram of Numerical Example 2.

11 is a short focus aberration curve diagram of Numerical Example 3. FIG.

FIG. 12 is an intermediate aberration curve diagram of Numerical Example 3.

FIG. 13 is a long focus aberration curve diagram of Numerical Example 3.

14 is a short focus aberration curve diagram of Numerical Example 4. FIG.

FIG. 15 is an intermediate aberration curve diagram of Numerical Example 4.

FIG. 16 is a long focus aberration curve diagram of Numerical Example 4.

FIG. 17 is an optical sectional view of a liquid crystal projector.

FIG. 18 is a partially enlarged view of a liquid crystal display panel with a microlens.

FIG. 19 is a partially enlarged view showing a vignetting state.

[Explanation of symbols]

 11 First Lens Group 12 Second Lens Group 13 Third Lens Group 14 Fourth Lens Group 15 Liquid Crystal Display Panel with Micro Lens SP Fixed Aperture S Short Focus Edge L Long Focus Edge

Claims (19)

[Claims] 1. A first lens having a positive refractive power in order from a large conjugate side.
The zoom lens is composed of a lens group, a second lens group having a negative refractive power, and another lens group. Zooming is performed by changing the lens group interval, and the focal length of the lens group having a positive refractive power arranged on the short conjugate side is f _4. A zoom lens that satisfies the following conditional expression when the short focal length of the entire system is f _s . 1 <f ₄ / f _s <3 2. The zoom lens according to claim 1, wherein the following conditional expression is satisfied when the back focus is bf _s when the conjugate point on the large conjugate side is assumed to be infinity. 0 ≦ bf _s / f _s <0.3 3. The third lens group having a positive refractive power and the lens group having a positive refractive power fixed to the short conjugate side, wherein the other lens group is a lens group having a positive refractive power and is configured to change from a short focal end to a long focal end of the entire system. 3. The zoom lens according to claim 1, wherein the distance between the first lens group and the second lens group increases and the distance between the second lens group and the third lens group decreases when the magnification is doubled. . 4. The first lens having a positive refractive power in order from the larger conjugate side.
It is composed of a lens group, a second lens group having a negative refractive power, and other lens groups. Zooming is performed by changing the lens group spacing, and the lens group on the short conjugate side has a fixed positive refractive power, A zoom lens characterized by satisfying the following conditional expression, where f _{s is the} short focal length and bf _s is the back focus when a large conjugate point is assumed to be infinity. 0 ≦ bf _s / f _s <0.3 5. A third lens group having a positive refracting power is arranged between the second lens group and a fourth lens group on the short conjugate side, and a change from a short focal end to a long focal end of the entire system. When the magnification is doubled, the distance between the first lens group and the second lens group increases, the distance between the second lens group and the third lens group decreases, and the focal length of the short conjugate side lens group becomes f ₄ The zoom lens according to claim 4, wherein the following conditional expression is satisfied. 1 <f ₄ / f _s <3 6. The zoom lens according to claim 5, further satisfying the following conditional expression. 0.15 <D _23s / D _34s <0.6, where D _{23s is} the air distance between the second lens unit and the third lens unit at the short focus end D _34s is the third lens unit and the second lens at the short focus end Group air spacing 7. The zoom lens according to claim 5, further satisfying the following conditional expression. 0.5 <f ₁ / f _s <1.5 0.2 <−f ₂ / f _s <0.5 0.4 <f ₃ / f _s <1.3 where f ₁ : of the first lens group Focal length f ₂ : Focal length of second lens group f ₃ : Focal length of third lens group 8. The zoom lens according to claim 5, further satisfying the following conditional expression. 0.16 <N _2p −N _2n <0.3 where N _2p : average value of refractive index of positive lens in the second lens group N _2n : average value of refractive index of negative lens in the second lens group 9. The third lens group is further separated by a largest air space in the third lens group, and has a third conjugate side.
9. The zoom lens according to claim 5, wherein the zoom lens comprises a front lens group and a third rear lens group on the small conjugate side, and satisfies the following conditional expression. 0.03 <D _3ab / f ₃ <0.2 where D _{3ab is} the air gap between the third front lens group and the third rear lens group 10. The second lens group comprises, in order from a large conjugate side, a negative lens having a strong power on a small conjugate side, a negative lens having a convex convex cemented surface toward a large conjugate side, and a strong negative lens on a large conjugate side. 10. The zoom lens according to claim 5, wherein the zoom lens comprises a positive lens having power. 11. The zoom lens according to claim 5, wherein a fixed diaphragm fixed to a small conjugate point is arranged between the third lens group and the fourth lens group. 12. The zoom lens according to claim 5, wherein the fourth lens group is composed of one positive single lens and satisfies the following conditional expression. -3.1 <SF ₄ <-0.3 where _{SF 4 = (r 4f + r} 4r) / (r 4f -r 4r) r 4f: curvature of the large conjugate side in the fourth lens group of positive single lens radius r _4r : radius of curvature on the small conjugate side of the positive single lens in the fourth lens group 13. 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 in order from the large conjugate side. The optical axis is configured to increase the air distance between the first lens group and the second lens group and decrease the air distance between the second lens group and the third lens group during zooming from the short focus end to the long focus end. A zoom lens that moves upward and satisfies the following conditional expression. 0.15 <where _{D 23s / D 34s <0.6,} D 23s: the second lens group and the air distance between the third lens group at the short focal end. D _34s : Air distance between the third lens group and the fourth lens group at the short focus end. 14. The zoom lens according to claim 13, further satisfying the following conditional expression. 0.5 <f ₁ / f _s <1.5 0.2 <−f ₂ / f _s <0.5 0.4 <f ₃ / f _s <1.3 where f ₁ : of the first lens group Focal length f ₂ : Focal length of second lens group f ₃ : Focal length of third lens group 15. The zoom lens according to claim 13, further satisfying the following conditional expression. 0.16 <N _2p −N _2n <0.3 where N _2p : average value of refractive index of positive lens in the second lens group N _2n : average value of refractive index of negative lens in the second lens group 16. The third lens group is composed of a third front lens group on the large conjugate side and a third rear lens group on the small conjugate side with a largest air space in the third lens group. The zoom lens according to any one of claims 13 to 15, characterized by satisfying the following conditional expression. 0.03 <D _3ab / f ₃ <0.2 where D _{3ab is} the air gap between the third front lens group and the third rear lens group 17. The second lens group comprises, in order from the large conjugate side, a negative lens having strong power on the small conjugate side, a cemented negative lens having a convex surface of the cemented surface facing the large conjugate side, and a strong lens on the large conjugate side. 17. The zoom lens according to claim 13, wherein the zoom lens comprises a positive lens having power. 18. The zoom lens according to claim 13, further comprising a fixed diaphragm fixed to a small conjugate point between the third lens group and the fourth lens group. 19. The zoom lens according to claim 13, wherein the fourth lens group is composed of one positive single lens and satisfies the following conditional expression. -3.1 <SF ₄ <-0.3 where _{SF 4 = (r 4f + r} 4r) / (r 4f -r 4r) r 4f: curvature of the large conjugate side in the fourth lens group of positive single lens radius r _4r : radius of curvature on the small conjugate side of the positive single lens in the fourth lens group