JP2000206409A - Zoom lens and projection device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a telecentric and compact zoom lens whose back focus is long while obtaining satisfactory optical performance. SOLUTION: This zoom lens is provided with a 1st lens group L1, having negative refractive power, a 2nd lens group L2 having positive refractive power, a 3rd lens group L3 having negative refractive power, a 4th lens group L4 having positive refractive power and a 5th lens group L5 having positive refractive power in turn from a large conjugate side. Then, when a variable power action is executed to a telephoto end from a wide angle end, the groups L2 and L4 are moved to the large conjugate side. Also it is provided with at least one aspherical-surface lens. Then, when the distance to a small conjugate surface from the pupil of a short conjugate side at the wide angle end when the conjugate length of a long conjugate side is infinity is defined as (tkw), and the focal distance of a whole system at the wide angle end is defined as (fw), the conditional expression of |tkw/fw|>4 is 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 more particularly to a zoom lens suitable for a projection lens of a projection apparatus for enlarging and projecting an original image fixed at a finite distance onto a screen.

[0002]

2. Description of the Related Art A negative lead type zoom lens, which is preceded by a lens group having a negative refractive power, has features such as relatively easy widening of the angle of view and maintaining optical performance even at a close-up shooting distance. ing. However, on the other hand, it has disadvantages such as an increase in the amount of movement of the lens group that moves during zooming, and difficulty in achieving high zooming.

[0003] A zoom lens in which these disadvantages are improved and the entire lens system is miniaturized and high zoom ratio is disclosed in, for example, JP-B-49-23912, JP-A-53-34539 and JP-A-57-34539. JP-163213, JP-A-58-
No. 4113, JP-A-63-241511, and JP-A-2-201310.

In each of these publications, a zoom lens is composed of four lens units of negative, positive, negative, and positive refractive power in order from the object side, and a predetermined lens unit is appropriately moved to change the magnification. It is carried out.

[0005]

By the way, a projection lens of a projection device for enlarging and projecting a display image on a screen includes:
In particular, the following conditions are required for a projection lens of an apparatus that uses a plurality of liquid crystal displays for each color light, combines images of the respective color lights displayed on the liquid crystal display, and projects the images with one projection lens.

(1) In order to eliminate the influence of the light distribution characteristics of the liquid crystal or the angle dependence of the color synthesizing dichroic mirror when synthesizing a plurality of color lights, it is viewed from the display image side (original image side, short conjugate side). A so-called telecentric optical system in which the pupil is far away.

(2) The back focus is long in order to secure a space for the color combining element interposed between the display and the projection lens.

(3) Since a display image is generally projected upward, the display body is used with its center position shifted with respect to the optical axis of the projection lens. As a result, an effective area to be used near the front lens is used. It is not symmetric with respect to the optical axis, but is biased upward. Therefore, some improvement is necessary because the diameter of the front lens becomes large.

In response to such requirements, in the above-described conventional zoom lens, the pupil position viewed from the short conjugate side is at a relatively close finite distance, and the back focus is hardly sufficiently long.

Further, assuming that two liquid crystal projectors A and B are used for superposition projection (stack projection) as shown in FIG. 21A, a conventional zoom lens is used as a projection lens. Since the distortion at the wide-angle end is relatively large, the projected image A on the screen S of the liquid crystal projector A has a pincushion-type distortion that increases toward the left side of the drawing as indicated by the solid line in FIG. The projected image B on the screen S of the liquid crystal projector B is shown in FIG.
As shown by the dotted line in FIG. 1 (b), the pincushion type distortion increases toward the right side of the drawing. Therefore, even if the position and size of the projected image are finely adjusted by each liquid crystal projector, a large pixel shift remains between the two projected images, and although the brightness is improved, it is difficult to view the projected image without a sense of resolution. There was a problem that only can be obtained.

An object of the present invention is to provide a compact zoom lens which is telecentric on the short conjugate side, has a long back focus, and has good optical performance.

[0012]

In order to achieve the above-mentioned object, a zoom lens according to the present invention comprises, in order from a long conjugate side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power,
A third lens group having a negative refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a positive refractive power. When zooming from a wide-angle end to a telephoto end, the second lens group A zoom lens for moving a fourth lens group to a long conjugate side, the zoom lens including at least one aspherical lens, and a short conjugate pupil on a short conjugate side at a wide angle end when a conjugate length on a long conjugate side is infinity. When the distance to the surface is tkw and the focal length of the entire system at the wide-angle end is fw, the conditional expression | tkw / fw |> 4 is satisfied.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a numerical example 1 to be described later.
FIG. 3 is a lens cross-sectional view of the zoom lens according to the first embodiment, the data of which is shown in FIG. The zoom lens according to the present embodiment includes a first lens unit L1 having a negative refractive power and a second lens unit L having a positive refractive power in order from a screen side (long conjugate side, left side in the figure) not shown.
2, the third lens unit L3 having a negative refractive power, and the fourth lens unit L3 having a positive refractive power
A lens unit L4, a fifth lens unit L5 having a positive refractive power,
When zooming from the wide-angle end to the telephoto end, the first
The lens unit L1 and the fifth lens unit L2 are fixed, and move the second lens unit L2 and the fourth lens unit L4 to the screen side, and also move the third lens unit L3 monotonously to the screen side. In the figure, D is a glass block corresponding to a cross dichroic prism or the like, and P is a liquid crystal panel (short conjugate plane) on which an image is displayed.

In this embodiment, the first lens unit L1
Is composed of, in order from the screen side, a positive lens having stronger power on the screen side than the liquid crystal panel P side, a negative meniscus lens having a convex surface facing the screen side, a biconcave lens, and a positive lens. This is an aspheric lens whose side surface is aspheric.

The reason for disposing the positive lens closest to the screen in the first lens unit L1 is to correct distortion. In particular, to provide a strong power to the screen side of the positive lens is to use a higher order distortion. This is for suppressing the occurrence of the occurrence. The second negative meniscus lens is arranged from the screen side of the first lens unit L1 in order to distribute the refraction of the off-axis light beam almost uniformly on each surface and to suppress the occurrence of coma aberration. The reason for using an aspherical surface is to reduce distortion. Further, by performing chromatic aberration correction on the liquid crystal panel P closest to the liquid crystal panel P of the first lens unit L1 having a low off-axis ray height, occurrence of high-order chromatic aberration of magnification is suppressed to a small extent.

The second lens unit L2 includes, in order from the screen side, a biconvex lens and a cemented lens in which a biconvex lens and a negative lens are cemented in order to favorably correct spherical aberration and longitudinal chromatic aberration. The third lens unit L3 includes a single biconcave lens having a large Abbe number in order to reduce fluctuations in chromatic aberration due to movement of the third lens unit. The fourth lens unit L4 is a negative lens having a strong power on the liquid crystal panel P side and a positive lens having a strong power on the liquid crystal panel P side in order from the screen side in order to mainly correct coma aberration and chromatic aberration of magnification of the off-axis light flux. It comprises a lens, a negative meniscus lens convex on the liquid crystal panel P side, and a positive lens having strong power on the liquid crystal panel P side. The fifth lens unit L5 includes one positive lens having strong power on the screen side for keeping the pupil (entrance pupil) viewed from the liquid crystal panel P side away and for correcting field curvature and distortion. Have been.

With such a configuration, a compact zoom lens that is telecentric on the short conjugate side, has a long back focus, and obtains good optical performance is realized. In particular, in this embodiment, the positive lens is arranged closest to the screen side of the first lens group,
By using an aspheric surface for the second negative meniscus lens, the occurrence of distortion is suppressed to an extremely small value.

(Embodiment 2) FIG. 2 is a numerical example 2 to be described later.
FIG. 6 is a lens cross-sectional view of the zoom lens according to a second embodiment, the data of which is shown in FIG. The zoom lens according to the present embodiment has a configuration similar to that of the zoom lens according to the first embodiment, but achieves a shorter projection distance (distance to a screen) by further reducing the focal length at the wide-angle end.

(Embodiment 3) FIG. 3 is a numerical example 3 to be described later.
FIG. 9 is a lens cross-sectional view of a zoom lens according to a third embodiment whose data is shown in FIG. This embodiment is an embodiment in which the first, fourth, and fifth lens groups have a different lens configuration from the second embodiment.

The first lens unit L1 of this embodiment comprises, in order from the screen, a negative meniscus lens having a convex surface facing the screen, a biconcave lens, and a positive meniscus lens having a convex surface facing the screen. Is an aspherical lens whose surface on the screen side is aspherical. The fourth lens unit L4 is arranged in order from the screen side.
Negative lens having stronger power on the screen side than the liquid crystal panel P side, positive lens having stronger power on the liquid crystal panel P side than the screen side, negative meniscus lens having a convex surface facing the liquid crystal panel P side, screen It is composed of a positive lens having a stronger power on the liquid crystal panel P side than on the side. The fifth lens unit L5 includes a positive lens having an aspheric surface on the surface on the liquid crystal panel P side.

By using aspherical surfaces for the first lens unit L1 and the fifth lens unit L5 where the height of off-axis rays is high, extremely small distortion is realized.

(Embodiment 4) FIG. 4 is a lens sectional view of a zoom lens according to Embodiment 4 showing data in Numerical Example 4 to be described later. The zoom lens according to the present embodiment is similar to the zoom lens according to the third embodiment.
, But with different numerical data.

(Embodiment 5) FIG. 5 is a lens sectional view of a zoom lens according to Embodiment 5 showing data in Numerical Example 5 described later. The zoom lens according to the present embodiment is similar to the zoom lens according to the fourth embodiment.
In the embodiment in which the fifth lens group is replaced with one positive lens and one negative lens, the fifth lens group has a two-lens configuration, so that an aspheric lens is not used for the fifth lens group.
The same effect as that of the fourth embodiment is realized.

Next, the features of each embodiment will be described.

(A) By giving a relatively strong positive refractive power to the fifth lens unit L5 closest to the liquid crystal panel P (display image), a telecentric system is realized. In particular, in the first to fourth embodiments, the fifth lens unit L5 is composed of only one positive lens having a strong convex surface facing the screen, thereby achieving both the correction of the field curvature and the distortion and the simplification of the configuration. ing.

(B) Second lens unit L2, third lens unit L
3. By moving the fourth lens unit L4 to perform zooming, the amount of movement of each group is reduced to shorten the overall length, and the distance from the pupil position as viewed from the screen side to the front lens is shortened. In addition, the diameter of the front lens determined by the off-axis oblique light beam can be reduced.

(C) Since the first lens unit L1 has negative refracting power, it has a retrofocus structure as a whole, and secures a long back focus for the space of a color combining element such as a cross dichroic prism. ing.

(D) The refractive power of each group is appropriately arranged,
By fixing the lens unit L1 during zooming, the fluctuation of the incident position of the off-axis oblique light beam with respect to the first lens unit L1 due to zooming is reduced, and the lens system has a simplified configuration and a constant overall length. .

(E) In the first and second embodiments, the positive lens having the stronger power on the screen side than the liquid crystal panel side on the screen side of the first lens unit L1, and at least one surface on the second side from the screen side Place a negative meniscus lens with the convex surface facing the screen side having an aspheric surface,
The distortion at the wide-angle end is reduced.

In the third and fourth embodiments, a negative meniscus lens having an aspherical surface on the screen side and a convex surface facing the screen side is disposed closest to the screen side of the first lens unit L1, and at least one aspherical lens is provided. To the fifth lens unit L5.
To reduce distortion at the wide-angle end.

In the fifth embodiment, a negative meniscus lens having an aspherical surface on the screen side and a convex surface facing the screen side is disposed closest to the screen side of the first lens unit L1.
At least one positive lens and at least one negative lens are arranged in the fifth lens group to reduce distortion at the wide-angle end.

(F) The focal lengths of the entire system at the wide-angle end and the telephoto end are respectively fw and ft, and the focal length of the first lens unit L1 is f.
1, the focal length of the second lens unit L2 is f2, the focal length of the third lens unit L3 is f3, the focal length of the fourth lens unit L4 is f4, the focal length of the fifth lens unit L5 is f5, and the screen at the wide-angle end. When the distance between the liquid crystal panel P and the pupil viewed from the liquid crystal panel P side (short conjugate side) when the conjugate length on the side (long conjugate side) is infinity is tkw, | tkw / fw |> 4 (1 0.8 <| f1 | / f2 <2 (2) The conditional expression 0.5 <f2 / 条件 (fw × ft) <1.5 (3) is satisfied.

Equation (1) limits the ratio of the distance between the pupil and the liquid crystal panel P as viewed from the liquid crystal panel P side and the focal length at the wide-angle end of the entire system. Is too close to the liquid crystal panel P, the angle of the off-axis chief ray in the display image becomes large, and the angle of incidence on the color combining element such as a cross dichroic prism disposed between the projection lens and the liquid crystal panel P changes. This is not good because color unevenness occurs on the screen due to a large difference around the image.

Equation (2) shows the second lens unit L which is the main zooming unit.
The relationship between the second lens group L1 and the first lens unit L1 is appropriately defined. When deviating from the lower limit of the expression (2), the first lens unit L1
Is large, and the distortion at the wide-angle end increases, which is not appropriate. On the other hand, if the value deviates from the upper limit value, it is necessary to increase the amount of movement of the second lens unit L2 in order to obtain a desired zoom ratio.

Equation (3) is to make the power of the main zooming unit appropriate. When the power exceeds the lower limit, an under field curvature occurs, which is not appropriate. On the other hand, if the value exceeds the upper limit, the amount of movement of the second lens unit L2 must be increased in order to obtain a desired zoom ratio, and the entire system becomes large, which is not appropriate.

In order to properly correct the curvature of field, the following conditional expression is satisfied: 0.9 <| f1 | / fw <2 (4)

If the value deviates from the lower limit of the expression (4), the power of the first lens unit L1 becomes too strong, so that the field curvature becomes excessive. If the value exceeds the upper limit, the power of the first lens unit L1 becomes too weak. The field curvature is undesirably low.

The change β2t / β2w accompanying the magnification change of the second lens unit L2, which is the main magnification unit, is Z2, and the change ft / fw of the focal length ft / fw of the entire system is Z. The movement amounts (difference between the wide-angle end position and the telephoto end position) of the second lens unit L2 and the fourth lens unit L4 during zooming are M2 and M4, respectively.
0.9 <Z2 / Z <1.1 (5) 0.5 <M2 / M4 <1.9 (6) 0.5 <M2 / (ft−fw) <1.5 (7) The following conditional expression is satisfied.

The equation (5) indicates that the second lens unit L2 is a zooming unit.
And the zoom ratio in the fourth lens unit L4. The third lens unit L3 preferably falls within this range in order to reduce the magnification upon zooming.

Equations (6) and (7) make the length of the entire lens and the amount of movement of each zooming unit appropriate. In particular, since the power of the fourth lens unit L4 tends to be weaker between the second lens unit L2 and the fourth lens unit L4, this range is preferable in order to appropriately perform the variable power sharing.

As described above, in the second lens unit L2 and the fourth lens unit L4, since the power of the fourth lens unit L4 tends to be weaker, 0.15 <f2 / f4 <0.9 (8 Satisfies the following conditional expression:

Equations (6) and (8) are conditions necessary for appropriately setting the Petzval sum while appropriately arranging the power and zooming of the main zooming unit.

When the back focus is bf, the following conditional expression is satisfied: 0.3 <bf / f5 <0.6 (9) 0.9 <| f1 | / bf <2.2 (10) The pupil position and distortion viewed from the liquid crystal panel P side of the entire system are appropriately set. The back focus bf is a distance (air conversion length) from the fifth lens unit L5 to the liquid crystal panel P. Equation (9) is a condition necessary for making the entire system appropriately telecentric. Equation (9)
If the upper limit is exceeded, the size increases, and if the lower limit is exceeded, distortion occurs. Equation (10) is also a condition for increasing the distance from the liquid crystal panel P side to the pupil as viewed from the liquid crystal panel P side so as to be telecentric while appropriately taking distortion.

Further, while appropriately arranging the power arrangement of each group,
1.0 <│f1│ / √ (fw × ft) <1.7 (11) 0.6 <│f3│ / √ (fw × ft) ) <2.0 (12) 1.1 <f4 / √ (fw × ft) <3.5 (13) 1.5 <f5 / √ (fw × ft) <3.0 (14) Is pleased.

Further, in order to reduce the chromatic aberration of magnification during zooming and to suppress its fluctuation, the third lens unit L3
Is constituted by a negative lens whose Abbe number ν3 is in the following range.

Ν3> 35 (15) Formula (15) preferably further satisfies ν3> 40 (15a).

In order to reduce high-order chromatic aberration of magnification, the average Abbe number ν1n of the negative lens constituting the first lens unit L1 satisfies the following conditional expression.

Ν1n> 55 (16) In order to satisfactorily correct the distortion, the fifth lens unit L5 includes one positive lens and satisfies the following conditional expression.

[0050]

[Outside 2] Here, R5f: the radius of curvature of the lens surface on the screen side of the fifth lens group R5r: the radius of curvature of the lens surface on the display image side of the fifth lens group In order to satisfactorily correct the distortion, the following conditional expression is satisfied. Is pleased.

0.15 <SF5 <1.5 (18) where, SF5 = (R5r + R5f) / (R5r−R5)
f)

The zoom lenses of the first to fifth embodiments satisfy all of the expressions (1) to (18) described above, but they do not necessarily have to satisfy all of the conditional expressions at the same time. Since the effects of the respective conditional expressions can be obtained separately, any combination of the expressions (1) to (18) can be taken depending on the specifications of the zoom lens.

(G) Focusing on a finite distance is the first
Although it is the simplest in terms of configuration to perform the operation with the lens unit L1, the third
The movement may be performed by moving the lens unit L3, the fifth lens unit L5, or a plurality of groups by different moving amounts. Also, the entire zoom lens is moved integrally, or the liquid crystal panel P
May be moved.

By configuring as shown in the first to fifth embodiments, a small-sized telecentric zoom lens having a simple configuration, a bright F-number of about 1.8, and suppressing the occurrence of distortion and lateral chromatic aberration is realized. be able to. By using such a zoom lens as a projection lens of an enlarged projection projection device, high-definition image projection can be performed. In addition, since distortion can be extremely reduced in the entire zoom range, even when superposition projection is performed using two or more liquid crystal projectors, occurrence of pixel shift can be extremely reduced, and bright and high definition can be achieved. A projection image is obtained.

The following are numerical examples. In each numerical example, ri is the radius of curvature of the i-th surface from the screen side, di is the distance between the i-th surface and the (i + 1) -th surface from the screen side, and ni is d of the i-th optical member from the screen side. The refractive index in the line, νi, is the Abbe number of the i-th optical member from the screen side.

The aspherical surface is represented by the following equation.

[0057]

[Outside 3] Here, x is the displacement value in the optical axis direction from the lens vertex, y is the distance from the optical axis, r is the paraxial radius of curvature, k is the conic constant, B
ＥE are aspherical coefficients.

FIGS. 6 to 8 are graphs showing various aberrations of the zoom lens of Numerical Example 1 (Embodiment 1) at the wide-angle end, at the intermediate focal length, and at the telephoto end, respectively. 9 to 11 are diagrams illustrating various aberrations of the zoom lens of Numerical Example 2 (Embodiment 2) at the wide-angle end, the intermediate focal length, and the telephoto end, respectively. Figures 12-14
9A and 9B are graphs showing various aberrations of the zoom lens according to Numerical Example 3 (Embodiment 3) at the wide-angle end, an intermediate focal length, and a telephoto end. 15 to 17 are graphs showing various aberrations of the zoom lens according to Numerical Example 4 (Embodiment 4) at the wide-angle end, the intermediate focal length, and the telephoto end. 18 to 20 are various aberration diagrams at the wide-angle end, an intermediate focal length, and a telephoto end of the zoom lens of Numerical Example 5 (Embodiment 5), respectively.

In each embodiment, the conditional expressions (1) to (1)
Table 1 shows the numerical values of 8).

[0060]

[Outside 4]

[0061]

[Outside 5]

[0062]

[Outside 6]

[0063]

[Outside 7]

[0064]

[Outside 8]

[0065]

[Table 1]

[0066]

As described above, according to the present invention,
A compact zoom lens that is telecentric on the small conjugate side, has a long back focus, and obtains good optical performance can be realized.

[Brief description of the drawings]

FIG. 1 is a lens cross-sectional view of a zoom lens according to a first embodiment.

FIG. 2 is a lens cross-sectional view of a zoom lens according to a second embodiment.

FIG. 3 is a sectional view of a zoom lens according to a third embodiment.

FIG. 4 is a sectional view of a zoom lens according to a fourth embodiment.

FIG. 5 is a sectional view of a zoom lens according to a fifth embodiment.

FIG. 6 is a diagram illustrating various aberrations of the zoom lens according to the first exemplary embodiment at a wide-angle end.

FIG. 7 is a diagram illustrating various aberrations of the zoom lens according to the first embodiment at an intermediate focal length.

FIG. 8 is a diagram illustrating various aberrations of the zoom lens according to the first exemplary embodiment at a telephoto end.

FIG. 9 is a diagram illustrating various aberrations of the zoom lens according to the second exemplary embodiment at the wide-angle end.

FIG. 10 is a diagram illustrating various aberrations of the zoom lens according to the second embodiment at an intermediate focal length.

FIG. 11 is a diagram illustrating various aberrations at the telephoto end of the zoom lens according to the second embodiment.

FIG. 12 is a diagram illustrating various aberrations of the zoom lens at a wide angle end according to the third exemplary embodiment.

FIG. 13 is a diagram illustrating various aberrations of the zoom lens according to the third embodiment at an intermediate focal length.

FIG. 14 is a diagram illustrating various aberrations at the telephoto end of the zoom lens according to the third embodiment;

FIG. 15 is a diagram illustrating various aberrations of the zoom lens at a wide angle end according to the fourth exemplary embodiment.

FIG. 16 is a diagram illustrating various aberrations of the zoom lens according to the fourth embodiment at an intermediate focal length.

FIG. 17 is a diagram illustrating various aberrations at the telephoto end of the zoom lens according to the fourth embodiment;

FIG. 18 is a diagram illustrating various aberrations of the zoom lens at a wide angle end according to the fifth exemplary embodiment.

FIG. 19 is a diagram illustrating various aberrations of the zoom lens according to the fifth embodiment at an intermediate focal length.

FIG. 20 is a diagram illustrating various aberrations at the telephoto end of the zoom lens according to Embodiment 5;

FIG. 21 is an explanatory diagram of a pixel shift at the time of superposition projection (stack projection).

[Explanation of symbols]

 L1 First lens group L2 Second lens group L3 Third lens group L4 Fourth lens group L5 Fifth lens group P Liquid crystal panel D Glass block

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H044 AC04 2H087 KA06 KA07 PA11 PA12 PA18 PB20 QA02 QA05 QA12 QA26 QA36 QA41 QA45 SA07 SA09 SA20 SA32 SA43 SA63 SA65 SA72 SA74 SA76 SB04 SB14 SB22 SB35 SB43 9A001 BB06 GG06

Claims (16)

[Claims] 1. A first lens having a negative refractive power in order from a long conjugate side.
A lens group, a second lens group having a positive refractive power, a third lens group having a negative refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a positive refractive power. A zoom lens for moving the second lens group and the fourth lens group to a long conjugate side when zooming to an end, wherein the zoom lens has at least one aspherical lens and has a long conjugate side with a conjugate length of infinity. When the distance from the short conjugate pupil to the short conjugate plane at the wide-angle end is tkw, and the focal length of the entire system at the wide-angle end is fw, | tkw / fw |> 4 is satisfied. And zoom lens. 2. The zoom lens according to claim 1, wherein said first lens group includes an aspheric lens. 3. The zoom lens according to claim 1, wherein said fifth lens group includes an aspherical lens. 4. The zoom lens according to claim 1, wherein the fifth lens group includes at least one positive lens and at least one negative lens. 5. When zooming from the wide-angle end to the telephoto end, the distance between the second lens group and the third lens group increases, and
5. The zoom lens according to claim 1, wherein the distance between the lens group and the fourth lens group decreases. 6. When zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group decreases, and
The zoom lens according to claim 5, wherein the distance between the lens and the fifth lens group increases. 7. The apparatus according to claim 1, wherein the second lens group has at least two positive lenses and at least one negative lens, and the third lens group has at least one negative lens. 7. The zoom lens according to any one of claims 1 to 6. 8. The focal length of the entire system at the wide-angle end is fw, the focal length of the entire system at the telephoto end is ft, and the focal length of the first lens group is f.
1. Assuming that the focal length of the second lens group is f2, the following conditional expression is satisfied: 0.8 <| f1 | / f2 <2 0.5 <| f2 / √ (fw × ft) | <1.5 8. The method according to claim 1, wherein
The zoom lens described. 9. The zoom lens according to claim 1, wherein a position of said third lens group at a telephoto end is on a conjugate side longer than a position of said third lens group at a wide-angle end. 10. The zoom lens according to claim 1, wherein the first lens group is fixed during zooming. 11. The apparatus according to claim 1, wherein the first lens group has a positive lens on the longest conjugate side.
The zoom lens described. 12. The first lens group includes, in order from a long conjugate side, a positive lens having stronger power on a larger conjugate side than a shorter conjugate side, a negative meniscus lens having a convex surface directed to a longer conjugate side, a biconcave lens, The zoom lens according to claim 11, comprising a positive lens. 13. A negative meniscus lens having a convex surface directed to the long conjugate side in order from the long conjugate side,
11. The zoom lens according to claim 1, comprising a biconcave lens and a positive lens, wherein at least one surface of the negative meniscus lens is aspheric. 14. The fifth lens group is composed of one positive lens, the radius of curvature of the lens surface on the large conjugate side of the positive lens is R5f, and the radius of curvature of the lens surface on the short conjugate side of the positive lens is R5f. When the radius of curvature is R5r, 2. The optical system according to claim 1, wherein the following conditional expression is satisfied.
3. The zoom lens according to 3. 15. An optical apparatus comprising the zoom lens according to claim 1. Description: 16. A display device for displaying an original image, and a projection lens for projecting the original image on a screen, wherein the projection lens is constituted by the zoom lens according to claim 1 to 14. Projection device.