JPH10133110A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens which has long back focus and also has distortion compensated excellently as a zoom lens consisting of three groups by making the front group of a 3rd group and its meniscus lens meet specific requirements. SOLUTION: This lens comprises a 1st group Gr1 with negative refracting power, a 2nd group Gr2 with positive refracting power, and the 3rd group Gr3 with positive refracting power in order from the enlargement side. The front group GrF of the 3rd group Gr3 comprises a positive meniscus lens M which has its convex surface on the enlargement side and two negative meniscus lenses having their concave surfaces on the reduction side in order from the enlargement side. The front group GrF and meniscus lens M meet the conditions of 0.80<|ϕF|.fS<1.30, 3<=|(rMB+rMA)/(rMA-rMA)|. Here, ϕF is the refracting power of the front group GrF, fS is the focal length of the whole system at the wide-angle end, and rMA and rMB are the radii of curvature of the enlargement-side and reduction-side surfaces of the meniscus lens M, respectively.

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 as a projection optical system for a projection apparatus (such as a liquid crystal projector for projecting an image on a liquid crystal panel onto a screen). is there.

[0002]

2. Description of the Related Art Conventionally, various types of zoom lenses have been known. For example, in order from the object side, the first lens unit includes a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power. JP-A-64-46717 discloses a zoom lens having a three-group configuration in which the second group moves in the optical axis direction such that the distance between the second group and the third group increases during zooming.

[0003]

A zoom lens is generally used as an imaging optical system for an imaging device (for example, a video camera) and as a projection optical system for a projection device (for example, a liquid crystal projector). Used and
There is. The zoom lens described in the above publication is a zoom lens used as an imaging optical system. Therefore, there is a problem that the back focus is too short and the distortion is not sufficiently corrected for use as a projection optical system.

When a zoom lens is used as a projection optical system, a long back focus is required because a space for disposing a dichroic prism or the like on the reduction side of the zoom lens is required. Further, when the zoom lens is used as a projection optical system, the distortion is not sufficiently corrected because a wide-angle region where the distortion increases is used to project a large image at a short projection distance.

The present invention has been made in view of these points, and an object of the present invention is to provide a zoom lens having a long back focus and excellent correction of distortion, which is suitable as a projection optical system. is there.

[0006]

In order to achieve the above object, a zoom lens according to a first aspect of the present invention includes, in order from a magnification side, a first lens unit having a negative refractive power and a second lens unit having a positive refractive power. And a third group having a positive refractive power. When zooming from the wide-angle end to the telephoto end, the second group is illuminated so that the distance between the second group and the third group is widened. In a zoom lens having a three-group configuration that moves in the axial direction, the third group includes, in order from the magnification side, a front group having a negative refractive power and a rear group having a positive refractive power, and the front group is located on the magnification side. A meniscus lens having a negative or weak positive refractive power with a convex surface is provided on the most enlarged side, the rear group includes at least two positive lenses, and the front group and the meniscus lens satisfy the following conditions. It is characterized by. 0.80 <| φF | · fS <1.33 ≦≦ (r _MB + r _MA ) / (r _MB −r _MA ) | where φF: refractive power of the front group, fS: focal length of the whole system at the wide-angle end, r _MA : radius of curvature of the enlarged side of the meniscus lens, r _MB : radius of curvature of the reduced side of the meniscus lens.

A zoom lens according to a second aspect of the present invention includes, in order from the enlargement side, a first group having a negative refractive power, a second group having a positive refractive power, a third group having a positive refractive power, Consisting of
In zooming from a wide-angle end to a telephoto end, a zoom lens having a three-group configuration in which the second group moves in the optical axis direction such that the distance between the second group and the third group increases. Consists of a front group having a negative refractive power and a rear group having a positive refractive power in order from the enlargement side, and the front group most preferably includes a meniscus lens having a negative or weak positive refractive power with a convex surface directed to the enlargement side. A cemented lens comprising a first lens having a positive refractive power with a convex surface facing the enlargement side and a second lens having a negative refractive power with a concave surface facing the reduction side, the meniscus lens being provided on the enlargement side in order from the enlargement side. Wherein the rear group includes at least two positive lenses, and the front group and the first and second lenses satisfy the following condition. 0.80 <| φF | · fS <1.30 3 ≦ | (r _M2B + r _M1A ) / (r _M2B −r _M1A ) | where φF is the refractive power of the front group, fS is the focal length of the whole system at the wide-angle end, r _M1A : radius of curvature of the enlarged side surface of the first lens, r _M2B : radius of curvature of the reduced side surface of the second lens.

A zoom lens according to a third aspect of the present invention includes, in order from the magnification side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power, Consisting of
In zooming from a wide-angle end to a telephoto end, a zoom lens having a three-group configuration in which the second group moves in the optical axis direction such that the distance between the second group and the third group increases. Is composed of a front group having a negative refractive power and a rear group having a positive refractive power in order from the enlargement side, wherein the front group has a positive refractive power whose convex surface faces the enlargement side in order from the most enlargement side. A lens and a second lens having a negative refractive power with a concave surface facing the reduction side, wherein the rear group includes at least two positive lenses, and the front group and the first and second lenses have the following conditions. Is satisfied. 0.80 <| φF | · fS <1.30 3 ≦ | (r _M2B + r _M1A ) / (r _M2B −r _M1A ) | where φF is the refractive power of the front group, fS is the focal length of the whole system at the wide-angle end, r _M1A : radius of curvature of the enlarged side surface of the first lens, r _M2B : radius of curvature of the reduced side surface of the second lens.

A zoom lens according to a fourth aspect of the present invention is the zoom lens according to the first to fourth aspects.
In the structure of any one of the third inventions, the first group may include at least two negative lenses and at least one positive lens.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a zoom lens embodying the present invention will be described with reference to the drawings. Note that the embodiment described below is a zoom lens suitable as a projection optical system for a projection device (for example, a liquid crystal projector), but is also suitable as an imaging optical system for an imaging device (for example, a video camera). It goes without saying that it can be used.

FIG. 1, FIG. 3, FIG. 5, FIG. 7, FIG. 9, FIG.
FIGS. 13, 15, and 17 are lens configuration diagrams respectively corresponding to the first to ninth embodiments, and [L] denotes a telephoto end.
(Long focal length end), [M] is middle (intermediate focal length state),
[S] indicates the lens arrangement at the wide-angle end (short focal length end). Also, in each figure, the surface with ri (i = 1,2,3, ...) is the i-th surface counted from the enlargement side, and di (i = 1,2,3, ...). The shaft upper surface interval marked with.) Is the i-th shaft upper surface interval counted from the enlargement side.

In the first to ninth embodiments, the first unit Gr1 having a negative refractive power, the second unit Gr2 having a positive refractive power, and the second unit Gr2 having a positive refractive power are arranged in this order from the enlargement side. 3rd group Gr
A three-group zoom lens comprising:
A dichroic prism PR is arranged on the reduction side of the group Gr3. Zooming is performed by changing the distance between each of the groups Gr1 to Gr3, from the wide-angle end [S] to the telephoto end.
In zooming to [L], the second lens unit Gr2 and the third lens unit G
The second lens unit Gr2 moves in the optical axis direction such that the distance from r3 is increased. The third group Gr3 includes, in order from the magnification side, a front group GrF having a negative refractive power and a rear group Gr having a positive refractive power.
R. The front group GrF includes at least one negative lens, and the rear group GrR includes at least two positive lenses. The detailed lens configuration of each group Gr1 to Gr3 in each embodiment will be described below.

<< Lens Configuration of First Group Gr1 >> In the first, second, and seventh embodiments, the first group Gr1 is a negative meniscus lens having a concave surface facing the reduction side in order from the enlargement side, and a biconcave lens. , And a positive meniscus lens having a convex surface facing the enlargement side. In the third embodiment, the first group Gr1 includes, in order from the enlargement side, a negative meniscus lens having a concave surface facing the reduction side and a positive meniscus lens having a convex surface facing the enlargement side. In the fourth to sixth embodiments, the first group Gr1 includes, in order from the enlargement side, a negative meniscus lens having a concave surface facing the reduction side, a positive meniscus lens having a convex surface facing the enlargement side, and a concave surface facing the reduction side. Made of negative meniscus lens. In the eighth embodiment, the first group Gr1 includes, in order from the enlargement side, a negative meniscus lens having a concave surface facing the reduction side and a biconvex positive lens. In the ninth embodiment, the first lens unit Gr1
Consists of two negative meniscus lenses having a concave surface facing the reduction side and a positive meniscus lens having a convex surface facing the enlargement side in order from the enlargement side.

<< Lens Configuration of Second Group Gr2 >> First and Seventh
In the embodiment, the second group Gr2 includes, in order from the enlargement side, a biconvex positive lens, and a cemented lens of a negative meniscus lens having a concave surface facing the reduction side and a biconvex positive lens. In the second embodiment, the second lens unit Gr2 includes:
In order from the enlargement side, it is composed of a biconvex positive lens, and a cemented lens of a biconvex positive lens and a negative meniscus lens having a concave surface facing the enlargement side. In the third and ninth embodiments, the second group Gr2 includes, in order from the enlargement side, a positive meniscus lens having a convex surface facing the enlargement side, a negative meniscus lens having a concave surface facing the reduction side, and a biconvex positive lens. Made up of In the fourth to sixth and eighth embodiments, the second lens unit Gr2
Comprises, in order from the enlargement side, a biconvex positive lens, a negative meniscus lens having a concave surface facing the reduction side, and a biconvex positive lens.

<< Lens Configuration of Front Group GrF of Third Group Gr3 >> In the first embodiment, the front group G of the third group Gr3
rF is composed of, in order from the enlargement side, a positive meniscus lens M having a convex surface facing the enlargement side and a negative meniscus lens having two concave surfaces facing the reduction side. In the second embodiment, the front group GrF of the third group Gr3 includes, in order from the enlargement side, a positive meniscus lens M having a convex surface facing the enlargement side and a biconcave negative lens. In the third and fourth embodiments, the front group GrF of the third group Gr3 includes, in order from the enlargement side, a negative meniscus lens M having a convex surface facing the enlargement side and a biconcave negative lens. In the fifth and ninth embodiments, the front group GrF of the third group Gr3 includes, in order from the enlargement side, a positive meniscus lens M1 having a convex surface facing the enlargement side and a negative meniscus lens M2 having a concave surface facing the reduction side. Cemented lens,
And a biconcave negative lens. 6th, 7th, 8th
In the embodiment, the front group GrF of the third group Gr3 is
A positive meniscus lens M1 having a convex surface facing the enlargement side and a negative meniscus lens M having a concave surface facing the reduction side in order from the enlargement side.
2 and a biconcave negative lens.

<< Lens Configuration of Rear Group GrR of Third Group Gr3 >> In the first embodiment, the rear group G of the third group Gr3 is
rR includes, in order from the enlargement side, a positive meniscus lens having a convex surface facing the reduction side and a positive meniscus lens having a convex surface facing the enlargement side. In the second and third embodiments, the rear unit GrR of the third unit Gr3 includes, in order from the enlargement side, a cemented lens of a negative meniscus lens having a concave surface facing the reduction side and a biconvex positive lens, and a biconvex lens. Consists of a positive lens. In the fourth and fifth embodiments, the third lens unit Gr
The third rear group GrR includes, in order from the enlargement side, a cemented lens of a negative meniscus lens having a concave surface facing the reduction side and a biconvex positive lens, and two biconvex positive lenses. Sixth
In the seventh and ninth embodiments, the rear group GrR of the third group Gr3 has, in order from the enlargement side, a positive meniscus lens having a convex surface directed to the reduction side, a biconvex positive lens, and a convex surface directed to the enlargement side. It consists of a positive meniscus lens. In the eighth embodiment, the rear unit GrR of the third unit Gr3 includes, in order from the enlargement side, two biconvex positive lenses and a positive meniscus lens having a convex surface facing the enlargement side.

<< Aspheric Surface >> In the eighth embodiment, the reduced side surface of the biconvex positive lens of the first unit Gr1 and the third unit Gr3
The reduced side surface of the biconcave negative lens is aspheric. First group G
The aspherical surface provided on the biconvex positive lens of r1 is an aspherical surface in which the positive refractive power increases as the distance from the center to the periphery increases. In the ninth embodiment, the first
The reduced side surface of the positive meniscus lens whose convex surface faces the enlarged side of the group Gr1 is an aspheric surface. The aspherical surface provided in the positive meniscus lens is an aspherical surface having such a shape that a central portion has a negative refractive power and a peripheral portion has a positive refractive power.

<< Characteristics of Third Group Gr3 >> As described above, the dichroic prism PR for color-synthesizing the light from the liquid crystal panel is disposed on the reduction side of the third group Gr3. For this reason, in each embodiment as a projection optical system,
A long back focus is required for arranging the dichroic prism PR, and a substantially telecentric property on the reduction side for preventing the occurrence of color shading is also required.

The third lens unit Gr3 of each embodiment has an inverted telephoto refractive power arrangement including a negative front lens unit GrF and a positive rear lens unit GrR. By employing such an inverse telephoto refractive power arrangement in the third lens unit Gr3, it is possible to secure a back focus required as a projection optical system.
The principal ray that has entered the third lens unit Gr3 is flipped up by the front lens unit GrF in a direction away from the optical axis, and then bent by the rear lens unit GrR so as to be parallel to the optical axis. With such a substantially telecentric property, it is possible to suppress the occurrence of color shading and improve the color reproducibility at the top, bottom, left and right of the screen.

<Refractive power of front group GrF> In the above-described reverse telephoto type refractive power arrangement, it is desirable that the front group GrF of the third group Gr3 satisfies the following conditional expression (1). 0.80 <| φF | · fS <1.30 (1) where φF is the refractive power of the front group GrF, and fS is the focal length of the entire system at the wide-angle end [S].

Conditional expression (1) defines the condition range of the refractive power of the front group GrF in relation to the entire system. If the lower limit of conditional expression (1) is exceeded, it will be impossible to secure a sufficient back focus as the projection optical system. Conversely, when the value exceeds the upper limit of the conditional expression (1), it becomes difficult to correct various aberrations (particularly, spherical aberration).

<Types of Front Group GrF> In the first to fourth embodiments, the front group GrF of the third group Gr3 is a meniscus lens having a negative or weak positive refractive power with a convex surface facing the enlargement side. In the fifth and ninth embodiments, the meniscus lens M further includes a first lens M1 having a positive refractive power with a convex surface facing the enlargement side and a concave surface on the reduction side. And a cemented lens with a second lens M2 having a negative refractive power. Further, in the sixth to eighth embodiments, the cemented lens is further divided into two lenses, a first lens M1 and a second lens M2, and the lens interval is used as an air lens. .

That is, the embodiments according to the present invention can be divided into the following three types. : Embodiment in which the meniscus lens M arranged on the most enlarged side of the front group GrF is composed of a meniscus-shaped single lens having a negative or weak positive refractive power with the convex surface facing the enlarged side (first to fourth embodiments) Embodiment). : The meniscus lens arranged on the most magnifying side of the front group GrF is a meniscus lens having a negative or weak positive refractive power with the convex surface facing the magnifying side, with the convex surface facing the magnifying side in order from the magnifying side. First lens M having positive refractive power
An embodiment (fifth and ninth embodiments) composed of a cemented lens of a first lens and a second lens M2 having a negative refractive power with a concave surface facing the reduction side.
Embodiment). : The front group GrF includes, in order from the enlargement side, a first lens M1 having a positive refractive power with a convex surface facing the enlargement side and a second lens M2 having a negative refractive power with a concave surface facing the reduction side. Embodiments in which the distance between the first lens M1 and the second lens M2 is used as an air lens (sixth to eighth embodiments).

In the embodiment, the first lens M1 and the second lens M1
The cemented lens composed of the lens M2 holds the same meniscus shape as the meniscus lens M in the embodiment. Thus, by using a meniscus-shaped cemented lens with the convex surface facing the enlarged side as a whole,
The distortion and the coma for each color can be corrected more favorably than in the embodiment using one meniscus lens M. Further, if the action of the air lens is used as in the embodiment, the coma aberration and the field curvature difference of each color can be corrected better than in the embodiment using one meniscus lens M.

<Zooming and Distortion> In a general wide-angle zoom lens, distortion increases in the minus direction on the wide-angle side. In the embodiments according to the present invention, the telephoto end
In zooming from [L] to the wide-angle end [S], the second lens group G
The second lens group G such that the distance between r2 and the third lens group Gr3 is reduced.
Since r2 is zoomed, the incident position of the off-axis light beam on the third lens unit Gr3 changes toward the optical axis (that is, the height from the optical axis decreases). Further, the meniscus lens M of the embodiment and the first and second lenses M of the embodiment are described.
The entrance and exit surfaces of 1 and M2 are convex toward the enlargement side. Since the off-axis light flux is incident on the lens M; M1 and M2 configured with such a surface toward the optical axis toward the wide-angle side, the distortion occurs in the minus direction on the entrance surface that is convex toward the enlargement side. Is corrected to be smaller on the wide angle side.
By the action of the convex surface on the magnifying side of the lens M; M1 and M2, a change in distortion on the telephoto side and the wide-angle side can be reduced.

<Shape Factor of Meniscus Lens M> In the embodiment in which the front group GrF satisfies the conditional expression (1), the meniscus lens M has the following conditional expression:
It is desirable to satisfy (2). 3 ≦ | (r _MB + r _MA ) / (r _MB −r _MA ) | (2) where r _{MA is the} radius of curvature of the enlarged side surface of the meniscus lens M, and r _{MB is the} radius of curvature of the reduced side surface of the meniscus lens M. is there.

Conditional expression (2) defines a condition range of the shape factor of the meniscus lens M for mainly correcting distortion well. Meniscus lens M
After the incident off-axis light beam is bent toward the optical axis on the enlarged side surface convex to the enlargement side, the light beam is bent on the reduced side surface in a direction away from the optical axis and emitted. At this time, the meniscus lens M
Satisfies the condition range of the conditional expression (2), the change of the angle of the off-axis light beam with respect to the optical axis on the incident side and the angle with respect to the optical axis on the exit side becomes small. By reducing the change in the angle, the meniscus lens M can satisfactorily correct the distortion balance between the telephoto side and the wide-angle side without adversely affecting other aberrations in the zoom type of this zoom lens. can do.

In the conditional expression (2), the meniscus lens M
Since the radius of curvature r _MA of the enlarged side and the radius of curvature r _MB of the reduced side have the same sign, exceeding the condition range of the conditional expression (2) means that the radius of curvature between the enlarged side and the reduced side of the meniscus lens M is large. difference (| r _MB -r _MA |) and is increased, the absolute value of the refractive power of the meniscus lens M is meant to increase. Therefore, if the condition range of the conditional expression (2) is exceeded, the angle of the above-described off-axis light beam with respect to the optical axis on the incident side and the angle with respect to the optical axis on the exit side become large. Without this, the balance of distortion on the telephoto side and the wide-angle side cannot be corrected. If the radius of curvature r _MA and the radius of curvature r _MB have exactly the same value, the corresponding value of the conditional expression (2) | (r _MB + r _MA ) / (r _MB −r
_MA ) | is infinite, but conditional expression (2) is | ( _rMB + _rMA ) /
(r _MB −r _MA ) | is infinite.

<Surface Shape of First and Second Lenses M1 and M2>
In the embodiment in which the front unit GrF satisfies the conditional expression (1), it is preferable that the first and second lenses M1 and M2 satisfy the following conditional expression (3). 3 ≦ | (r _M2B + r _M1A ) / (r _M2B −r _M1A ) | (3) where r _{M1A is the} radius of curvature of the enlarged side surface of the first lens M1, r _{M2B is the} curvature of the reduced side surface of the second lens M2. Radius.

Conditional expression (3) mainly defines a condition range of the surface shape corresponding to the shape factor of the first and second lenses M1 and M2 for favorably correcting distortion. The first and second lenses M1 and M2 bend the incoming off-axis luminous flux toward the optical axis on the enlarged side surface convex to the enlarged side of the first lens M1, and then on the reduced side surface of the second lens M2. Bend in the direction away from the optical axis and emit. At this time,
When the second lenses M1 and M2 satisfy the conditional range of the conditional expression (3), a change in the angle of the off-axis light beam with respect to the optical axis on the incident side and the angle with respect to the optical axis on the exit side becomes small. By reducing the change in the angle, the first and second lenses M1, M2
In the zoom type of this zoom lens, it is possible to satisfactorily correct the balance of distortion on the telephoto side and the wide-angle side without adversely affecting other aberrations.

In the conditional expression (3), the radius of curvature r _M1A of the enlarged side surface of the first lens M1 and the radius of curvature r _M2B of the reduced side surface of the second lens M2 have the same sign. Exceeding the range means that the difference between the radius of curvature of the enlarged side surface and the reduced side surface of the first and second lenses M1 and M2 (| r _M2B -r _M1A |)
Increases, and the absolute value of the combined refractive power of the first and second lenses M1 and M2 increases. Therefore,
Exceeding the conditional range of the conditional expression (3) causes a large change in the angle of the above-described off-axis light beam with respect to the optical axis on the incident side and the angle with respect to the optical axis on the exit side, which adversely affects other aberrations. Therefore, the balance between the distortion on the telephoto side and the distortion on the wide-angle side cannot be corrected. The radius of curvature r _M1A
And the radius of curvature r _M2B have exactly the same value, the conditional expression
The corresponding value | (r _M2B + r _M1A ) / (r _M2B −r _M1A ) | of (3) is infinite, but | (r _M2B + r _M1A ) / (r _M2B )
−r _M1A ) | is infinite.

<Air lens formed by first and second lenses M1 and M2> As in the embodiment, two lenses M
In an embodiment in which the distance between M1 and M2 is used as an air lens, the first and second lenses M1 and M2 have the following conditional expressions
It is desirable to satisfy the condition (4) and the conditional expression (5). 0 <d _M1M2 / fS <0.1 (4) -0.006 <(1 / r _M2A ) − (1 / r _M1B ) <0.002 (5) where d _M1M2 is the difference between the first lens M1 and the second lens M2. On-axis air spacing, fS: focal length of the entire system at the wide-angle end [S], r _M1B : radius of curvature of the reduced side surface of the first lens M1, r _M2A : radius of curvature of the enlarged side surface of the second lens M2.

The conditional expressions (4) and (5) define a conditional range for the air lens formed between the first positive lens M1 and the second negative lens M2. When the value exceeds the upper limit of the conditional expression (4), the air gap between the first lens M1 and the second lens M2 becomes too large.
If the upper limit or the lower limit of (5) is exceeded, the difference in the radius of curvature between the reduced side surface of the first lens M1 and the enlarged side surface of the second lens M2 becomes too large. For this reason, in either case, the distortion cannot be satisfactorily corrected.

<Abbe Number of Meniscus Lens M>
As in the second embodiment, in the embodiment in which the meniscus lens M disposed on the most enlarged side of the front group GrF is a single meniscus lens having a positive refractive power, the meniscus lens M is as follows. It is desirable to satisfy the conditional expression (6). 18 <ν _M <30 (6) where ν _M is the Abbe number of the meniscus lens M.

The conditional expression (6) defines a condition range of the Abbe number of the meniscus lens M having a positive refractive power. If the value exceeds the range of conditional expression (6), it becomes impossible to correct lateral chromatic aberration in a well-balanced manner between the wide-angle side and the telephoto side.

<Abbe Number of First and Second Lenses M1 and M2> In the embodiment, the first and second lenses M
1, M2 preferably satisfies the following conditional expression (7). -300 <ν _M1M2 <30 (7) where, ν _M1M2 is a combined Abbe number of the first lens M1 and the second lens M2, and is defined by the following equation (7A). {1 / (f _M1 · ν _M1 )} + {1 / (f _M2 · ν _M2 )} = {1 / (f _M1M2 · ν _M1M2 )} (7A) where f _M1 : focal point of the first lens M1 Distance, f _M2 : focal length of second lens M2, f _M1M2 : composite focal length of first lens M1 and second lens M2, ν _M1 : Abbe number of first lens M1, ν _M2 : second lens M2 Abbe number.

Conditional expression (7) satisfies the first and second lenses M1, M
The condition range of the Abbe number of 2 is defined. When the condition range of the conditional expression (7) is exceeded, similarly to the case of the conditional expression (6),
The chromatic aberration of magnification cannot be corrected with good balance between the wide-angle side and the telephoto side.

<Third lens unit Gr3 during zooming> In the embodiments satisfying the above conditional expressions (1) and (2) or (3), the third lens unit Gr3 must be fixed during zooming. Is desirable. If the position of the third group Gr3 is fixed during zooming, a large component (eg, a dichroic prism PR arranged on the reduction side of the third group Gr3) required in the projection optical system can be fixed. This is advantageous in terms of the lens barrel configuration. For example, since the lens barrel configuration can be simplified, the cost can be easily reduced.

<Refractive power of the third lens unit Gr3>
Embodiment satisfying (1) and conditional expression (2) or (3)
Preferably satisfies the following conditional expression (8). 0.40 <φ3 · fS <0.70 (8) where φ3 is the refractive power of the third lens unit Gr3, and fS is the focal length of the entire system at the wide-angle end [S].

Conditional expression (8) defines the condition range of the refractive power of the third lens unit Gr3 in relation to the entire system. If the upper limit of conditional expression (8) is exceeded, various aberrations (particularly, spherical aberration and coma) will deteriorate, so that the F-number cannot be reduced. Therefore, it becomes difficult to obtain a bright zoom lens. Conversely, if the lower limit of conditional expression (8) is exceeded, the refractive power of the third lens unit Gr3 will be too small, so that the amount of movement of the first lens unit Gr1 and the second lens unit Gr2 for achieving the same zoom range will be large. Become. Therefore, it becomes difficult to obtain a compact zoom lens.

<< Refractive power of first group Gr1 and second group Gr2 >>
The first lens unit Gr1 and the second lens unit Gr2 satisfy the above-described conditional expression (1) and conditional expression (2) or (3) and perform zooming.
It is desirable that Embodiment 1 to move satisfy the following conditional expression (9). 0.5 <| φ1 | / φ2 <0.75 (9) where φ1: refractive power of the first lens unit Gr1, φ2: refractive power of the second lens unit Gr2.

Conditional expression (9) indicates that the first lens unit Gr1 and the second lens unit Gr1
2 (especially, a condition range regarding the trajectory of the moving group during zooming). Conditional expression (9)
Approaching the upper limit, the first lens unit Gr1 is at the telephoto end [L] and at the wide-angle end.
It will be located on the enlarged side in [S]. As a result, the overall length of the lens at the telephoto end [L] increases, and it becomes difficult to obtain a compact zoom lens. Conversely, when approaching the lower limit of conditional expression (9), the first lens unit Gr1 is located at the telephoto end [L] and on the reduction side at the wide-angle end [S].
As a result, the amount of peripheral light decreases at the wide-angle end [S]. In order to prevent a decrease in the peripheral light amount, it is necessary to increase the lens diameter of the first group Gr1 and the second group Gr2. However, when the lens diameter of the first group Gr1 and the second group Gr2 is increased,
It becomes difficult to obtain a compact zoom lens.

<< Features of First Group Gr1 >> Conditional Expression (1)
In the embodiments satisfying the conditional expression (2) or (3), it is preferable that the first group Gr1 includes at least two negative lenses and at least one positive lens. First
When the group Gr1 is configured as described above, it is possible to reduce distortion on the under side caused by a light beam incident on the periphery of the negative first group Gr1 on the wide-angle side. First group Gr
This is because, if the negative power of 1 is shared between the two lenses, the angle of the light beam with respect to the lens surface is reduced, and the negative distortion mainly generated in the negative lens of the first group Gr1 is reduced. Therefore, it is advantageous in correcting the distortion by the positive lens or the like of the first group Gr1.

<Aspherical surface of the first lens unit Gr1>
Embodiment satisfying (1) and conditional expression (2) or (3)
In the above, as in the eighth embodiment, at least one surface of the first group Gr1 having a positive refractive power is provided with an aspherical surface having a shape such that the positive refractive power increases as the distance from the center to the periphery increases. It is desirable to do. When the aspherical surface having such a shape is arranged in the first lens unit Gr1, the effect of correcting the distortion generated on the under side by the negative lens toward the over side, particularly at the wide-angle end [S], is increased.

In the embodiments satisfying the above-mentioned conditional expression (1) and conditional expressions (2) or (3), the weak negative refractive power in the first lens unit Gr1 is changed as in the ninth embodiment. May be arranged on at least one surface having a shape such that the central part has a negative refractive power and the peripheral part has a positive refractive power. Even if the aspherical surface having such a shape is arranged in the first lens unit Gr1, similarly to the case of the above-described aspherical surface, the distortion generated on the under side by the negative lens particularly at the wide-angle end [S] is reduced to the over side. The effect of correcting is large.

The above-mentioned aspherical surface is desirably provided on the positive lens in the first group Gr1. When an aspheric surface is arranged on the positive lens, it is desirable that the positive lens satisfies the following conditional expression (10). 1.45 <na <1.60 (10) where na is a refractive index of a positive lens provided with an aspheric surface.

Conditional expression (10) defines the refractive index of the positive lens provided with the aspherical surface. A positive lens provided with an aspheric surface is a low refractive index medium that satisfies conditional expression (10), and is more effective in correcting the above-described distortion. The same effect on distortion can also be obtained by configuring the negative lens in the first group Gr1 with a medium having a high refractive index exceeding the upper limit of the conditional expression (10) and providing an aspherical surface having a completely opposite shape. Can be achieved. However, it is not preferable to provide an aspherical surface in the high refractive index medium because the cost increases.

[0048]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of a zoom lens embodying the present invention will be described more specifically with reference to construction data, aberration diagrams, and the like. Examples 1 to 1 given here as examples
Reference numeral 9 corresponds to the first to ninth embodiments, respectively, and is a lens configuration diagram illustrating the first to ninth embodiments.
(FIG. 1, FIG. 3, FIG. 5, FIG. 7, FIG. 9, FIG. 11, FIG. 13, FIG. 15, FIG. 17) show the corresponding lens configurations of Examples 1 to 9, respectively.

In the construction data of each embodiment, ri (i = 1, 2, 3,...) Is the radius of curvature of the i-th surface counted from the enlargement side, and di (i = 1, 2, 3,. ..) indicates the i-th axial distance from the magnification side, and Ni (i = 1,2,3, ...), νi (i = 1,2,
3,...) Indicate the refractive index (Nd) and Abbe number (νd) of the i-th lens with respect to the d-line counted from the magnification side. In the construction data, the axial top surface interval (variable interval) changed by zooming is from the telephoto end (long focal length end) [L] to the middle (intermediate focal length state) [M] to the wide angle end (short focal length end) [S ]
Is the axial distance between each group. The focal lengths f and F of the entire system corresponding to these focal length states [L], [M], [S].
The number FNO is also shown.

Also, the surface marked with * for the radius of curvature ri is:
It indicates that the surface is constituted by an aspherical surface, and is defined by the following equation (AS) representing the surface shape of the aspherical surface.

[0051]

(Equation 1)

In the equation (AS), X: displacement amount from the reference plane in the optical axis direction, Y: height in the direction perpendicular to the optical axis, C: paraxial curvature, ε: quadratic surface parameter , Ai: the i-th order aspheric coefficient.

<< Example 1 >> f = 82.5-65.0-55.0 FNO = 2.97-2.67-2.50 [Radius of curvature] [Shaft upper surface interval] [Refractive index] [Abbe number] {First group Gr1... Negative} r1 = 862.232 d1 = 4.000 N1 = 1.62041 ν1 = 60.29 r2 = 44.140 d2 = 10.000 r3 = -162.503 d3 = 3.000 N2 = 1.62041 ν2 = 60.29 r4 = 195.625 d4 = 0.500 r5 = 88.362 d5 = 5.000 N3 = 1.84666 ν3 = 23.82 r6 = 418.176 d6 = 3.000 to 15.766 to 26.707 {Second group Gr2 ... positive} r7 = 107.383 d7 = 5.000 N4 = 1.61800 ν4 = 63.39 r8 = -111.942 d8 = 0.500 r9 = 70.519 d9 = 3.000 N5 = 1.84666 ν5 = 23.82 r10 = 37.867 d10 = 7.000 N6 = 1.61800 ν6 = 63.39 r11 = -420.978 d11 = 23.041 ~ 9.969 ~ 2.500 {3rd group Gr3 ... positive} (front group GrF ... negative) r12 = 35.819 d12 = 6.000 N7 = 1.80518 ν7 = 25.43 r13 = 59.423 d13 = 3.000 r14 = 188.974 d14 = 3.000 N8 = 1.74000 ν8 = 31.72 r15 = 36.572 d15 = 8.000 r16 = 536.386 d16 = 4.000 N9 = 1.84666 ν9 = 23.82 r17 = 53.063 d17 = 20.500 (Rear group GrR… correct) r18 = -1063.366 d18 = 6.000 N10 = 1.62041 ν10 = 60.29 r19 = -78.508 d19 = 0.100 r20 = -724.743 d20 = 7.5 00 N11 = 1.62041 ν11 = 60.29 r21 = -97.491 d21 = 0.100 r22 = 61.183 d22 = 8.000 N12 = 1.51680 ν12 = 64.20 r23 = 263.940 d23 = 5.000 {Dichroic prism PR} r24 = ∞ d24 = 40.000 N13 = 1.51680 ν13 = 64.20 r25 = ∞

Example 2 f = 82.5 to 65.0 to 55.0 FNO = 2.95 to 2.66 to 2.50 [Radius of curvature] [Shaft upper surface interval] [Refractive index] [Abbe number] {First group Gr1 ... negative} r1 = 1276.194 d1 = 4.000 N1 = 1.51680 ν1 = 64.20 r2 = 48.518 d2 = 9.000 r3 = -1827.252 d3 = 4.000 N2 = 1.51680 ν2 = 64.20 r4 = 252.429 d4 = 1.000 r5 = 59.903 d5 = 6.500 N3 = 1.80518 ν3 = 25.43 r6 = 83.140 d6 = 2.000 ~ 20.893 ~ 37.086 {Second group Gr2 ... positive} r7 = 142.301 d7 = 6.000 N4 = 1.69680 ν4 = 56.47 r8 = -125.949 d8 = 0.500 r9 = 143.769 d9 = 9.000 N5 = 1.69680 ν5 = 56.47 r10 = -47.833 d10 = 3.000 N6 = 1.75520 ν6 = 27.51 r11 = -643.803 d11 = 23.612 ~ 10.177 ~ 2.500 {3rd group Gr3 ... positive} (front group GrF ... negative) r12 = 33.100 d12 = 8.000 N7 = 1.84666 ν7 = 23.82 r13 = 33.554 d13 = 8.000 r14 = -146.016 d14 = 4.000 N8 = 1.68150 ν8 = 36.64 r15 = 43.148 d15 = 15.000 (rear group GrR ... positive) r16 = 493.140 d16 = 4.000 N9 = 1.80518 ν9 = 25.43 r17 = 85.960 d17 = 15.000 N10 = 1.69680 ν10 = 56.47 r18 = -71.017 d18 = 0.500 r19 = 93.480 d19 = 12.000 N11 = 1.69680 ν11 = 56.4 7 r20 = -271.857 d20 = 5.000 {Dichroic prism PR} r21 = ∞ d21 = 40.000 N12 = 1.51680 ν12 = 64.20 r22 = ∞

<< Embodiment 3 >> f = 82.5-65.0-55.0 FNO = 3.02-2.69-2.50 [radius of curvature] [axis top surface interval] [refractive index] [Abbe number] {first group Gr1... Negative} r1 = 676.585 d1 = 4.000 N1 = 1.61800 ν1 = 63.39 r2 = 45.769 d2 = 11.163 r3 = 44.004 d3 = 4.000 N2 = 1.84666 ν2 = 23.82 r4 = 50.240 d4 = 2.000 to 17.471 to 30.732 {Second-group Gr2… correct} r5 = 62.527 d5 = 5.000 N3 = 1.61800 ν3 = 63.39 r6 = 754.256 d6 = 0.500 r7 = 82.261 d7 = 3.000 N4 = 1.80518 ν4 = 25.43 r8 = 41.588 d8 = 2.000 r9 = 54.541 d9 = 7.000 N5 = 1.61800 ν5 = 63.39 r10 = -137.617 d10 = 27.7 ~ 3.375 ~ 2.000 {3rd group Gr3 ... positive} (front group GrF ... negative) r11 = 33.190 d11 = 8.000 N6 = 1.84666 ν6 = 23.82 r12 = 32.840 d12 = 14.000 r13 = -103.203 d13 = 4.000 N7 = 1.68150 ν7 = 36.64 r14 = 45.848 d14 = 10.000 (GrR in rear group ... positive) r15 = 5254.861 d15 = 4.000 N8 = 1.80518 ν8 = 25.43 r16 = 93.889 d16 = 12.000 N9 = 1.69680 ν9 = 56.47 r17 = -63.501 d17 = 0.500 r18 = 68.713 d18 = 16.000 N10 = 1.61800 ν10 = 63.39 r19 = -170.704 d19 = 5.000 (Dichroic Prism PR} r20 = ∞ d20 = 40.000 N11 = 1.51680 ν11 = 64.20 r21 = ∞

Example 4 f = 82.5 to 65.0 to 55.0 FNO = 3.02 to 2.69 to 2.50 [Radius of curvature] [Shaft upper surface interval] [Refractive index] [Abbe number] {First group Gr1... Negative} r1 = 154.353 d1 = 4.000 N1 = 1.61800 ν1 = 63.39 r2 = 40.773 d2 = 10.392 r3 = 42.203 d3 = 7.000 N2 = 1.70055 ν2 = 30.11 r4 = 58.991 d4 = 7.517 r5 = 839.835 d5 = 3.000 N3 = 1.61800 ν3 = 63.39 r6 = 141.920 d6 = 3.000 to 18.869 to 32.472 {Second group Gr2 ... positive} r7 = 68.935 d7 = 5.000 N4 = 1.61800 ν4 = 63.39 r8 = -1402.564 d8 = 0.500 r9 = 82.107 d9 = 3.000 N5 = 1.80518 ν5 = 25.43 r10 = 40.768 d10 = 2.000 r11 = 50.572 d11 = 7.000 N6 = 1.61800 ν6 = 63.39 r12 = -172.006 d12 = 27.634 ~ 11.640 ~ 2.500 {3rd group Gr3 ... positive} (front group GrF ... negative) r13 = 31.907 d13 = 8.000 N7 = 1.84666 ν7 = 23.82 r14 = 30.613 d14 = 14.000 r15 = -94.551 d15 = 4.000 N8 = 1.68150 ν8 = 36.64 r16 = 47.744 d16 = 10.000 (Rear group GrR ... positive) r17 = 1274.275 d17 = 4.000 N9 = 1.80518 ν9 = 25.43 r18 = 107.683 d18 = 12.000 N10 = 1.69680 ν10 = 56.47 r19 = -75.076 d19 = 0.500 r20 = 82.235 d20 = 12.000 N 11 = 1.61800 ν11 = 63.39 r21 = -175.539 d21 = 1.000 r22 = 624.333 d22 = 7.000 N12 = 1.61800 ν12 = 63.39 r23 = -285.428 d23 = 5.000 {Dichroic prism PR} r24 = ∞ d24 = 40.000 N13 = 1.51680 ν13 = 64.20 r25 = ∞

<< Example 5 >> f = 82.5-65.0-55.0 FNO = 3.02-2.69-2.50 [Radius of curvature] [Shaft upper surface interval] [Refractive index] [Abbe number] {First group Gr1... Negative} r1 = 163.467 d1 = 4.000 N1 = 1.61800 ν1 = 63.39 r2 = 41.485 d2 = 12.992 r3 = 47.235 d3 = 7.000 N2 = 1.75520 ν2 = 27.51 r4 = 63.469 d4 = 5.500 r5 = 758.369 d5 = 3.000 N3 = 1.61800 ν3 = 63.39 r6 = 150.096 3.000-19.614-33.855 {Second group Gr2 ... positive} r7 = 70.851 d7 = 5.000 N4 = 1.61800 ν4 = 63.39 r8 = -298.018 d8 = 0.500 r9 = 86.403 d9 = 3.000 N5 = 1.84666 ν5 = 23.82 r10 = 42.033 d10 = 2.000 r11 = 48.512 d11 = 7.000 N6 = 1.61800 ν6 = 63.39 r12 = -197.716 d12 = 23.600 to 10.173 to 2.500 {3rd group Gr3 ... positive} (front group GrF ... negative) r13 = 35.555 d13 = 8.000 N7 = 1.80741 ν7 = 31.59 r14 = 126.223 d14 = 3.000 N8 = 1.80420 ν8 = 46.50 r15 = 30.845 d15 = 12.000 r16 = -77.498 d16 = 4.000 N9 = 1.72100 ν9 = 33.40 r17 = 59.063 d17 = 10.000 (Rear group GrR… correct) r18 = 1235.208 d18 = 4.000 N10 = 1.80518 ν10 = 25.43 r19 = 93.250 d19 = 12.000 N11 = 1.69680 ν11 = 56.47 r20 = -72.649 d20 = 0.500 r21 = 87.408 d21 = 12.000 N12 = 1.61800 ν12 = 63.39 r22 = -319.520 d22 = 1.000 r23 = 134.980 d23 = 7.000 N13 = 1.61800 ν13 = 63.39 r24 = -2269.684 d24 = 5.000 ｛Dichroic prism PR} r25 = ∞ d25 = 40.000 N14 = 1.51680 ν14 = 64.20 r26 =

<< Embodiment 6 >> f = 82.5-65.0-55.0 FNO = 2.97-2.67-2.50 [Radius of curvature] [Shaft upper surface interval] [Refractive index] [Abbe number] {First group Gr1 ... negative} r1 = 230.274 d1 = 4.000 N1 = 1.62041 ν1 = 60.29 r2 = 43.747 d2 = 12.992 r3 = 54.128 d3 = 7.000 N2 = 1.84666 ν2 = 23.82 r4 = 70.294 d4 = 5.500 r5 = 878.850 d5 = 3.000 N3 = 1.62041 ν3 = 60.29 r6 = 199.785 d 3.000 ~ 20.043 ~ 34.652 {Second group Gr2 ... positive} r7 = 72.660 d7 = 5.000 N4 = 1.61800 ν4 = 63.39 r8 = -220.035 d8 = 0.500 r9 = 87.713 d9 = 3.000 N5 = 1.84666 ν5 = 23.82 r10 = 43.317 d10 = 2.000 r11 = 48.919 d11 = 7.000 N6 = 1.61800 ν6 = 63.39 r12 = -277.691 d12 = 23.069〜 9.980〜 2.500 {3rd group Gr3 ... positive} (front group GrF ... negative) r13 = 37.693 d13 = 6.000 N7 = 1.84666 ν7 = 23.82 r14 = 107.578 d14 = 2.000 r15 = 103.889 d15 = 3.000 N8 = 1.80741 ν8 = 31.59 r16 = 31.574 d16 = 12.000 r17 = -68.013 d17 = 4.000 N9 = 1.84666 ν9 = 23.82 r18 = 73.566 d18 = 14.000 (GrR in the rear group ... positive) r19 = -488.890 d19 = 9.000 N10 = 1.62041 ν10 = 60.29 r20 = -57.701 d20 = 0.100 r 21 = 134.275 d21 = 9.000 N11 = 1.62041 ν11 = 60.29 r22 = -208.852 d22 = 0.100 r23 = 70.235 d23 = 9.000 N12 = 1.51680 ν12 = 64.20 r24 = 525.351 d24 = 5.000 {Dichroic prism PR} r25 = ∞ d25 = 40.000 N13 = 1.51680 ν13 = 64.20 r26 = ∞

Example 7 f = 82.5 to 65.0 to 55.0 FNO = 3.01 to 2.69 to 2.50 [Radius of curvature] [Shaft upper surface interval] [Refractive index] [Abbe number] {First group Gr1 ... negative} r1 = 1155.375 d1 = 3.000 N1 = 1.62041 ν1 = 60.29 r2 = 45.295 d2 = 10.000 r3 = -489.891 d3 = 2.700 N2 = 1.62041 ν2 = 60.29 r4 = 148.763 d4 = 0.100 r5 = 77.002 d5 = 5.000 N3 = 1.75520 ν3 = 27.51 r6 = 509.009 d6 = 1.500-18.911-33.836 {Second group Gr2 ... correct} r7 = 59.810 d7 = 5.000 N4 = 1.61800 ν4 = 63.39 r8 = -16136.841 d8 = 0.100 r9 = 76.557 d9 = 2.200 N5 = 1.84666 ν5 = 23.82 r10 = 40.218 d10 = 2.000 r11 = 48.575 d11 = 5.800 N6 = 1.61800 ν6 = 63.39 r12 = -171.636 d12 = 20.664 ~ 8.469 ~ 1.500 {3rd group Gr3 ... positive} (front group GrF ... negative) r13 = 36.489 d13 = 6.000 N7 = 1.75520 ν7 = 27.51 r14 = 153.417 d14 = 3.000 r15 = 243.127 d15 = 2.200 N8 = 1.74000 ν8 = 31.72 r16 = 30.516 d16 = 11.500 r17 = -90.478 d17 = 2.200 N9 = 1.84666 ν9 = 23.82 r18 = 77.337 d18 = 18.000 (positive GrR ... ) r19 = -289.606 d19 = 7.300 N10 = 1.62041 ν10 = 60.29 r20 = -57.779 d20 = 0.1 00 r21 = 243.162 d21 = 5.700 N11 = 1.62041 ν11 = 60.29 r22 = -183.238 d22 = 0.100 r23 = 71.282 d23 = 7.500 N12 = 1.62041 ν12 = 60.29 r24 = 361.925 d24 = 5.000 {Dichroic prism PR} r25 = ∞ d25 = 40.000 N13 = 1.51680 ν13 = 64.20 r26 = ∞

Example 8 f = 72.5 to 59.0 to 48.3 FNO = 2.97 to 2.67 to 2.50 [Radius of curvature] [Shaft upper surface interval] [Refractive index] [Abbe number] {First group Gr1 ... negative} r1 = 1556.687 d1 = 3.000 N1 = 1.69680 ν1 = 56.47 r2 = 43.952 d2 = 12.000 r3 = 245.668 d3 = 9.100 N2 = 1.58340 ν2 = 30.23 r4 * = -263.429 d4 = 3.000 to 19.718 to 39.667 {Second group Gr2… correct} r5 = 73.385 d5 = 5.000 N3 = 1.61800 ν3 = 63.39 r6 = -1167.352 d6 = 3.000 r7 = 65.715 d7 = 3.000 N4 = 1.84666 ν4 = 23.82 r8 = 45.705 d8 = 2.000 r9 = 58.016 d9 = 5.000 N5 = 1.61800 ν5 = 63.39 r10 = -249.272 d10 = 20.255 ~ 10.367 ~ 2.500 {3rd group Gr3 ... positive} (front group GrF ... negative) r11 = 36.070 d11 = 6.000 N6 = 1.71736 ν6 = 29.42 r12 = 145.958 d12 = 2.000 r13 = 602.177 d13 = 3.000 N7 = 1.75450 ν7 = 32.83 r14 = 30.657 d14 = 14.000 r15 = -407.953 d15 = 4.000 N8 = 1.84666 ν8 = 23.82 r16 * = 55.298 d16 = 10.000 (Rear group GrR ... positive) r17 = 210.544 d17 = 7.500 N9 = 1.51680 ν9 = 64.20 r18 =- 72.462 d18 = 0.100 r19 = 232.260 d19 = 7.000 N10 = 1.51680 ν10 = 64.20 r20 = -96.967 d20 = 0.100 r21 = 66.285 d21 = 8.500 N11 = 1.51680 ν11 = 64.20 r22 = 1665.917 d22 = 5.000 {Dichroic prism PR} r23 = ∞ d23 = 40.000 N12 = 1.51680 ν12 = 64.20 r24 = ∞

[Aspherical surface coefficient] r4: ε = 1.0000 A4 = -0.11319 × 10 ^-5 A6 = 0.12489 × 10 ^-9 A8 = -0.47125 × 10 ^-12 r16: ε = 1.0000 A4 = -0.96751 × 10 ^-6 A6 = -0.72732 × 10 ^-9 A8 = -0.63656 × 10 ^-12

Example 9 f = 72.5 to 59.0 to 48.3 FNO = 2.97 to 2.67 to 2.50 [Radius of curvature] [Shaft upper surface interval] [Refractive index] [Abbe number] {First group Gr1 ... negative} r1 = 394.515 d1 = 3.000 N1 = 1.62041 ν1 = 60.29 r2 = 42.736 d2 = 12.000 r3 = 1340.770 d3 = 2.500 N2 = 1.62041 ν2 = 60.29 r4 = 148.339 d4 = 0.100 r5 = 88.727 d5 = 6.500 N3 = 1.58340 ν3 = 30.23 r6 * = 2897.123 = 3.000-19.168-38.462 {Second group Gr2 ... positive} r7 = 79.565 d7 = 5.000 N4 = 1.61800 ν4 = 63.39 r8 = 987.596 d8 = 3.000 r9 = 68.314 d9 = 3.000 N5 = 1.84666 ν5 = 23.82 r10 = 38.820 d10 = 2.000 r11 = 44.052 d11 = 6.000 N6 = 1.61800 ν6 = 63.39 r12 = -130.793 d12 = 20.859〜10.634〜 2.500 {3rd group Gr3 ... positive} (front group GrF ... negative) r13 = 40.530 d13 = 8.000 N7 = 1.80518 ν7 = 25.43 r14 = 153.636 d14 = 3.000 N8 = 1.65446 ν8 = 33.86 r15 = 30.126 d15 = 12.000 r16 = -120.615 d16 = 4.000 N9 = 1.84666 ν9 = 23.82 r17 = 63.866 d17 = 14.000 (Rear group GrR… correct) r18 = -175.064 d18 = 5.600 N10 = 1.62041 ν10 = 60.29 r19 = -56.865 d19 = 0.100 r20 = 119.748 d20 = 8.2 00 N11 = 1.51680 ν11 = 64.20 r21 = -158.512 d21 = 0.100 r22 = 63.645 d22 = 9.000 N12 = 1.51680 ν12 = 64.20 r23 = 793.405 d23 = 5.000 {Dichroic prism PR} r24 = ∞ d24 = 40.000 N13 = 1.51680 ν13 = 64.20 r25 = ∞

[Aspherical surface coefficient] r6: ε = 1.0000 A4 = -0.57067 × 10 ^-6 A6 = -0.13108 × 10 ^-9 A8 = 0.26152 × 10 ^-13

Table 1 shows the conditional expressions (1) to (1) in each embodiment.
0), ie, conditional expression (1): | φF | · fS, conditional expression (2): | (r _MB + r _MA ) / (r _MB −r _MA ) |, conditional expression
(3): | (r _M2B + r _M1A ) / (r _M2B −r _M1A ) |, conditional expression
(4): d _M1M2 / fS, Conditional expression (5): (1 / r _M2A ) − (1 / r
_M1B), conditional expression (6): ν _M, the conditional expression (7): ν _M1M2, conditional expression
(8): φ3 · fS, conditional expression (9): | φ1 | / φ2, conditional expression
(10): na}.

[0065]

[Table 1]

FIGS. 2, 4, 6, 8, 10, and 1
2, FIG. 14, FIG. 16, and FIG. 18 are aberration diagrams respectively corresponding to Examples 1 to 9 (the optical system including the dichroic prism PR). Each aberration diagram shows various aberrations at the long focal length end [L], the middle [M], and the short focal length end [S].
(Y ′: image height). In each aberration diagram, the solid line (d)
Represents the aberration with respect to the d-line, the dashed line (g) represents the aberration with respect to the g-line, and the dashed line (SC) represents the sine condition. A broken line (DM) and a solid line (DS) represent astigmatism with respect to the d-line on the meridional surface and the sagittal surface, respectively.

When each of the above embodiments is used as a projection optical system of a liquid crystal projector, the screen surface is originally an image surface and the liquid crystal panel surface is an object surface. Each of them is a reduction system (for example, an imaging optical system), and the optical performance is evaluated on the liquid crystal panel surface with the screen surface being regarded as the object surface.

[0068]

As described above, according to the first to fourth aspects of the present invention, it is possible to realize a zoom lens suitable for a projection optical system having a long back focus and excellent correction of distortion. Further, according to the fourth aspect, it is possible to reduce the distortion on the under side caused by the light beam incident on the peripheral portion of the first group on the wide angle side.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of a first embodiment (Example 1).

FIG. 2 is an aberration diagram of the first embodiment.

FIG. 3 is a lens configuration diagram of a second embodiment (Example 2).

FIG. 4 is an aberration diagram of the second embodiment.

FIG. 5 is a lens configuration diagram of a third embodiment (Example 3).

FIG. 6 is an aberration diagram of the third embodiment.

FIG. 7 is a lens configuration diagram of a fourth embodiment (Example 4).

FIG. 8 is an aberration diagram of the fourth embodiment.

FIG. 9 is a lens configuration diagram of a fifth embodiment (Example 5).

FIG. 10 is an aberration diagram of the fifth embodiment.

FIG. 11 is a lens configuration diagram of a sixth embodiment (Example 6).

FIG. 12 is an aberration diagram of the sixth embodiment.

FIG. 13 is a lens configuration diagram of a seventh embodiment (Example 7).

FIG. 14 is an aberration diagram of the seventh embodiment.

FIG. 15 is a diagram illustrating a lens configuration according to an eighth embodiment (Example 8).

FIG. 16 is an aberration diagram of the eighth embodiment.

FIG. 17 is a lens configuration diagram of a ninth embodiment (Example 9).

FIG. 18 is an aberration diagram of the ninth embodiment.

[Explanation of symbols]

 Gr1 First group Gr2 Second group Gr3 Third group GrF Front group M Meniscus lens M1 First lens M2 Second lens GrR Rear group PR Dichroic prism

Claims (4)

[Claims] 1. A first group having a negative refractive power, a second group having a positive refractive power, and a third group having a positive refractive power are arranged in order from the enlargement side. In zooming to an end, in a zoom lens having a three-group configuration in which the second group moves in the optical axis direction such that the distance between the second group and the third group is increased, the third group is arranged from the enlargement side. The front group includes a front group having a negative refractive power and a rear group having a positive refractive power in order, and the front group includes a meniscus lens having a negative or weak positive refractive power with a convex surface directed to the magnifying side on the most magnifying side. The rear group is at least 2
0.80 <| φF | · fS <1.33 ≦ | (r _MB + r _MA ) / (r), wherein the front lens unit and the meniscus lens satisfy the following condition: _MB- r _MA ) |, where φF: refractive power of the front group, fS: focal length of the entire system at the wide-angle end, r _MA : radius of curvature of the enlarged side of the meniscus lens, r _MB : curvature of the reduced side of the meniscus lens Radius. 2. A first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power. In zooming to an end, in a zoom lens having a three-group configuration in which the second group moves in the optical axis direction so that the distance between the second group and the third group increases, the third group is arranged from the enlargement side. The front group includes a front group having a negative refractive power and a rear group having a positive refractive power in order, and the front group includes a meniscus lens having a negative or weak positive refractive power with a convex surface directed to the magnifying side on the most magnifying side. The meniscus lens is a cemented lens of a first lens having a positive refractive power with a convex surface facing the enlargement side and a second lens having a negative refractive power with a concave surface facing the reduction side in order from the enlargement side; The rear group includes at least two positive lenses, and the front group and the first group The second
0.80 <| φF | · fS <1.33 ≦ | (r _M2B + r _M1A ) / (r _M2B −r _M1A ) | Refractive power, fS: focal length of the entire system at the wide-angle end, r _M1A : radius of curvature of the enlarged side surface of the first lens, r _M2B : radius of curvature of the reduced side surface of the second lens. 3. A first unit having a negative refractive power, a second unit having a positive refractive power, and a third unit having a positive refractive power are arranged in order from the magnification side. In zooming to an end, in a zoom lens having a three-group configuration in which the second group moves in the optical axis direction such that the distance between the second group and the third group is increased, the third group is arranged from the enlargement side. A front lens group having a negative refractive power and a rear lens group having a positive refractive power in order, and the front lens group includes a first lens having a positive refractive power with a convex surface facing the enlargement side in order from the most enlarged side and a reduction side. A second lens having a negative refractive power with a concave surface facing the rear surface, wherein the rear group includes at least two positive lenses, and the front group and the first and second lenses satisfy the following condition: 0.80 <| φF | · fS <1.30 3 ≦ | (r _M2B + r _M1A ) / (r _{M2 B−} r _M1A ) |, where φF: refractive power of the front group, fS: focal length of the entire system at the wide-angle end, r _M1A : radius of curvature of the enlarged side of the first lens, r _M2B : reduced side of the second lens Is the radius of curvature of. 4. The zoom lens according to claim 1, wherein the first group includes at least two negative lenses and at least one positive lens.