Zoom lens system

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens system, and particularly to a zoom lens system suitable, for example, for use as a projection optical system in an image projection apparatus (such as a liquid crystal projector for projecting an image from a liquid crystal panel onto a screen).
2. Description of the Prior Art
Various types of zoom lens systems are known. For example, Japanese Laid-open Patent Application No. S64-46717 discloses a three-unit zoom lens system that consists of, from the object side 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 and that performs zooming from the wide-angle end to the telephoto end by moving the second lens unit along the optical axis in such a way that the distance between the second and third lens units increases.
Some zoom lens systems are designed for use as an image-sensing optical system in an image sensing apparatus (e.g. a video camera), whereas other zoom lens systems are designed for use as a projection optical system in an image projection apparatus (e.g. a liquid crystal projector). The zoom lens system disclosed in the above-mentioned Japanese Laid-open Patent Application No. S64-46717 is designed as an image-sensing optical system, and therefore, when it is used as a projection optical system, it suffers from its short back focal length and insufficient correction of distortion.
The reason why a zoom lens system to be used as a projection optical system needs to have a relatively long back focal length is that it is necessary to secure a space for a dichroic prism or the like on the reduction side of the zoom lens system. The reason why a zoom lens system to be used as a projection optical system needs to have relatively high distortion correction performance is that, in order to produce as large a projected image as possible at as short a projection distance as possible, it is necessary to use the wide-angle range of the zoom lens system where large distortion is inevitable.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a zoom lens system that has a sufficiently long back focal length and sufficiently high distortion correction performance for use as a projection optical system.
Note that, in the following descriptions, an "optical power" refers to a quantity that is represented as a reciprocal of a focal length, and thus refers not only to a deflection at an interface between media having different refractive indices, but also to a deflection or the like due to diffraction or due to distribution of varying refractive indices within a medium.
To achieve the above object, according to one aspect of the present invention, a zoom lens system is provided with, from the enlargement side, a first lens unit having a negative optical power; a second lens unit having a positive optical power; a third lens unit having a negative optical power, said third lens unit comprising, at its enlargement side end, a meniscus lens element having a convex surface on the enlargement side; and a fourth lens unit having a positive optical power, said fourth lens unit including at least two positive lens elements. In this zoom lens system, said second lens unit moves along the optical axis so that a distance between said second lens unit and third lens unit increases during zooming from a shortest focal length condition to a longest focal length condition. Moreover, in this zoom lens system, said third lens unit moves along the optical axis so that a distance between said third lens unit and fourth lens unit decreases during zooming from a shortest focal length condition to a longest focal length condition. Furthermore, in this zoom lens unit, the following conditions are fulfilled:
0.30<.vertline..phi.3.vertline..multidot.fS<0.90
3.ltoreq..vertline.(r.sub.MB +r.sub.MA)/(r.sub.MB -r.sub.MA).vertline.
where .phi.3 represents an optical power of the third lens unit; fS represents a focal length of the entire zoom lens in the shortest focal length condition; r.sub.MB represents a radius of curvature of the enlargement side surface of the meniscus lens element; and r.sub.MA represents a radius of curvature of the reduction side surface of the meniscus lens element.
According to another aspect of the present invention, a zoom lens system is provided with, from the enlargement side, a first lens unit having a negative optical power; a second lens unit having a positive optical power; and a third lens unit having a positive optical power, said third lens unit consisting of, from the enlargement side, a front lens sub-unit having a negative optical power and a rear lens sub-unit having a positive optical power, said front lens sub-unit comprising, at its enlargement side end, a meniscus lens element having a convex surface on the enlargement side, said rear lens sub-unit including two positive lens elements. In this zoom lens system, said second lens unit moves along the optical axis so that a distance between said second lens unit and third lens unit increases during zooming from a shortest focal length condition to a longest focal length condition. Moreover, in this zoom lens system, the following conditions are fulfilled:
0.30<.vertline..phi.F.vertline.fS<0.90
3.ltoreq..vertline.(r.sub.MB +r.sub.MA)/(r.sub.MB -r.sub.MA).vertline.
where .phi.F represents an optical power of the front lens sub-unit; fS represents a focal length of the entire zoom lens in the shortest focal length condition; r.sub.MB represents a radius of curvature of the enlargement side surface of the meniscus lens element; and r.sub.MA represents a radius of curvature of the reduction side surface of the meniscus lens element.

BRIEF DESCRIPTION OF THE DRAWINGS
This and other objects and features of this invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the accompanied drawings in which:
FIGS. 1A to 1C are lens arrangement diagrams of a first embodiment of the invention;
FIGS. 2A to 2I are aberration diagrams of the first embodiment:
FIGS. 3A to 3C are lens arrangement diagrams of a second embodiment of the invention;
FIGS. 4A to 4I are aberration diagrams of the second embodiment;
FIGS. 5A to 5C are lens arrangement diagrams of a third embodiment of the invention;
FIGS. 6A to 6I are aberration diagrams of the third embodiment:
FIGS. 7A to 7C are lens arrangement diagrams of a fourth embodiment of the invention;
FIGS. 8A to 8I are aberration diagrams of the fourth embodiment;
FIGS. 9A to 9C are lens arrangement diagrams of a fifth embodiment of the invention;
FIGS. 10A to 10I are aberration diagrams of the fifth embodiment;
FIGS. 11A to 11C are lens arrangement diagrams of a sixth embodiment of the invention;
FIGS. 12A to 12I are aberration diagrams of the sixth embodiment;
FIGS. 13A to 13C are lens arrangement diagrams of a seventh embodiment of the invention;
FIGS. 14A to 14I are aberration diagrams of the seventh embodiment;
FIGS. 15A to 15C are lens arrangement diagrams of an eighth embodiment of the invention;
FIGS. 16A to 16I are aberration diagrams of the eighth embodiment;
FIGS. 17A to 17C are lens arrangement diagrams of a ninth embodiment of the invention;
FIGS. 18A to 18I are aberration diagrams of the ninth embodiment:
FIGS. 19A to 19C are lens arrangement diagrams of a tenth embodiment of the invention;
FIGS. 20A to 20I are aberration diagrams of the tenth embodiment;
FIGS. 21A to 21C are lens arrangement diagrams of an eleventh embodiment of the invention:
FIGS. 22A to 22I are aberration diagrams of the eleventh embodiment;
FIGS. 23A to 23C are lens arrangement diagrams of an twelfth embodiment of the invention;
FIGS. 24A to 24I are aberration diagrams of the twelfth embodiment;
FIGS. 25A to 25C are lens arrangement diagrams of a thirteenth embodiment of the invention;
FIGS. 26A to 26I are aberration diagrams of the thirteenth embodiment;
FIGS. 27A to 27C are lens arrangement diagrams of a fourteenth embodiment of the invention;
FIGS. 28A to 28I are aberration diagrams of the fourteenth embodiment;
FIGS. 29A to 29C are lens arrangement diagrams of a fifteenth embodiment of the invention;
FIGS. 30A to 30I are aberration diagrams of the fifteenth embodiment;
FIGS. 31A to 31C are lens arrangement diagrams of a sixteenth embodiment of the invention;
FIGS. 32A to 32I are aberration diagrams of the sixteenth embodiment;
FIGS. 33A to 33C are lens arrangement diagrams of a seventeenth embodiment of the invention;
FIGS. 34A to 34I are aberration diagrams of the seventeenth embodiment;
FIGS. 35A to 35C are lens arrangement diagrams of an eighteenth embodiment of the invention;
FIGS. 36A to 36I are aberration diagrams of the eighteenth embodiment;
FIGS. 37A to 37C are lens arrangement diagrams of a nineteenth embodiment of the invention;
FIGS. 38A to 38I are aberration diagrams of the nineteenth embodiment;
FIGS. 39A to 39C are lens arrangement diagrams of a twentieth embodiment of the invention;
FIGS. 40A to 40I are aberration diagrams of the twentieth embodiment;
FIGS. 41A to 41C are lens arrangement diagrams of a twenty-first embodiment of the invention; and
FIGS. 42A to 42I are aberration diagrams of the twenty-first embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, zoom lens systems embodying the present invention will be described with reference to the drawings. All the embodiments described hereafter are designed for use as a projection optical system in an image projection apparatus (e.g. a liquid crystal projector). However, it should be understood that all the embodiments are also suitable for use as an imagesensing optical system in an image-sensing apparatus (e.g. a video camera).
FIGS. 1A-1C, 3A-3C, 5A-5C, 7A-7C, 9A-9C, 11A-11C, 13A-13C, 15A-15C, 17A-17C, 19A-19C, 21A-21C, 23A-23C, 25A-25C, 27A-27C, 29A-29C, 31A-31C, 33A-33C, 35A-35C, 37A-37C, 39A-39C, and 41A-41C are lens construction diagrams of the zoom lens systems of first to twenty-first embodiments, respectively, of the invention. Of these diagrams, FIGS. 1A, 3A, 5A, 7A, 9A, 11A, 13A, 15A, 17A, 19A, 21A, 23A, 25A, 27A, 29A, 31A, 33A, 35A, 37A, 39A, and 41A illustrate the lens arrangement in the telephoto-end condition (longest-focal-length condition) �L!, FIGS. 1B, 3B, 5B, 7B, 9B, 11B, 13B, 15B, 17B, 19B, 21B, 23B, 25B, 27B, 29B, 31B, 33B, 35B, 37B, 39B, and 41B illustrate the lens arrangement in the middle condition (middle-focal-length condition) �M!, and FIGS. 1C, 3C, 5C, 7C, 9C, 11C, 13C, 15C, 17C, 19C, 21C, 23C, 25C, 27C, 29C, 31C, 33C, 35C, 37C, 39C, and 41C illustrate the lens arrangement in the wide-angle-end condition (shortest-focal-length condition) �S!. In these lens arrangement diagrams, ri (i=1, 2, 3, . . . ) represents the i-th surface from the enlargement side, and di (i=1, 2, 3, . . . ) represents the i-th axial distance from the enlargement side.
Of these 21 embodiments, the first to twelfth embodiments are four-unit zoom lens systems of a negative-positive-negative-positive constitution, and the thirteenth to twenty-first embodiments are three-unit zoom lens systems of a negative-positive-positive constitution.
<<Embodiments 1 to 12>>
The first to twelfth embodiments are four-unit zoom lens systems each constituted of, from the enlargement side a first lens unit Gr1 having a negative refractive power, a second lens unit Gr2 having a positive refractive power, a third lens unit Gr3 having a negative refractive power, and a fourth lens unit Gr4 having a positive refractive power. In addition, a dichroic prism PR is disposed on the reduction side of the fourth lens unit Gr4. All of these zoom lens systems perform zooming by varying the distances between the first to fourth lens units Gr1 to Gr4; specifically, during zooming from the wide-angle end �S! to the telephoto end �L!, the second lens unit Gr2 is moved along the optical axis in such a way that the distance between the second and third lens units Gr2 and Gr3 increases, and, at the same time, the third lens unit Gr3 is moved along the optical axis in such a way that the distance between the third and fourth lens units Gr3 and Gr4 decreases. The third lens unit Gr3 includes at least one negative lens element, and the fourth lens unit Gr4 includes at least two positive lens elements. The constitution of the first to fourth lens units Gr1 to Gr4 in each embodiment will be described in more detail below.
<The Constitution of the First Lens Unit Gr1>
In the first and fourth embodiments, the first lens unit Gr1 consists of, from the enlargement side, a negative meniscus lens element concave to the reduction side, a negative biconcave lens element, and a positive meniscus lens element convex to the enlargement side. In the second, seventh to tenth, and twelfth embodiments, the first lens unit Gr1 consists of, from the enlargement side, two negative meniscus lens elements both concave to the reduction side, and a positive meniscus lens element convex to the enlargement side. In the third embodiment, the first lens unit Gr1 consists of, from the enlargement side, a negative meniscus lens element concave to the reduction side, a negative biconcave lens element, and a positive biconvex lens element. In the fifth and sixth embodiments, the first lens unit Gr1 consists of, from the enlargement side, a negative meniscus lens element concave to the reduction side, and a positive meniscus lens element convex to the enlargement side. In the eleventh embodiment, the first lens unit Gr1 consists of, from the enlargement side, two negative meniscus lens elements both concave to the reduction side, and a positive biconvex lens element.
<The Constitution of the Second Lens Unit Gr2>
In the first embodiment, the second lens unit Gr2 consists of, from the enlargement side, a positive biconvex lens element, a negative meniscus lens element concave to the reduction side, and a positive biconvex lens element. In the second, and eighth to tenth embodiments, the second lens unit Gr2 consists of, from the enlargement side, a negative meniscus lens element concave to the reduction side, and a doublet lens element formed by joining together a positive biconvex lens element and a negative meniscus lens element concave to the enlargement side. In the third embodiment, the second lens unit Gr2 consists of, from the enlargement side, a positive biconvex lens element, a negative meniscus lens element concave to the reduction side, and a positive meniscus lens element convex to the enlargement side. In the fourth embodiment, the second lens unit Gr2 consists of, from the enlargement side, a positive biconvex lens element, and a doublet lens element formed by joining together a positive biconvex lens element and a negative biconcave lens element. In the fifth and sixth embodiments, the second lens unit Gr2 consists of, from the enlargement side, a positive biconvex lens element, and a doublet lens element formed by joining together a positive biconvex lens element and a negative meniscus lens element concave to the enlargement side. In the seventh embodiment, the second lens unit Gr2 consists of, from the enlargement side, a positive biconvex lens element, and a negative meniscus lens element concave to the enlargement side. In the eleventh and twelfth embodiments, the second lens unit Gr2 consists of, from the enlargement side, a positive meniscus lens element convex to the enlargement side, a negative meniscus lens element concave to the reduction side, and a positive biconvex lens element.
<The Constitution of the Third Lens Unit Gr3>
In the first, second, eleventh, and twelfth embodiments, the third lens unit Gr3 consists of, from the enlargement side, a positive meniscus lens element convex to the enlargement side, and a negative biconcave lens element. In the third, fourth, and seventh to ninth embodiments, the third lens unit Gr3 consists of, from the enlargement side, a doublet lens element formed by joining together a positive biconvex lens element and a negative biconcave lens element, and a negative biconcave lens element. In the fifth and tenth embodiments, the third lens unit Gr3 consists of, from the enlargement side, a positive biconvex lens element, and two negative biconcave lens elements. In the sixth embodiment, the third lens unit Gr3 consists of, from the enlargement side, a positive biconvex lens element, a negative meniscus lens element concave to the reduction side, and a negative biconcave lens element.
<The Constitution of the Fourth Lens Unit Gr4>
In the first, second, eleventh, and twelfth embodiments, the fourth lens unit Gr4 consists of, from the enlargement side, a negative biconcave lens element, a positive meniscus lens element convex to the reduction side, a positive biconvex lens element, and a positive meniscus lens element convex to the enlargement side. In the third to fifth, seventh, and eighth embodiments, the fourth lens unit G4 consists of, from the enlargement side, a doublet lens element formed by joining together a negative biconcave lens element and a positive biconvex lens element, a positive biconvex lens element, and a positive meniscus lens element convex to the enlargement side. In the sixth embodiment, the fourth lens unit Gr4 consists of, from the enlargement side, a positive meniscus lens element convex to the reduction side, a doublet lens element formed by joining together a positive biconvex lens element and a negative meniscus lens element concave to the enlargement side, and a positive biconvex lens element. In the ninth and tenth embodiments, the fourth lens unit Gr4 consists of, from the enlargement side, a negative biconcave lens element, two positive biconvex lens elements, and a positive meniscus lens element convex to the enlargement side.
<Aspherical Surface>
In the eleventh embodiment, the reduction-side surface of the positive biconvex lens element included in the first lens unit Gr1 is an aspherical surface. This aspherical surface provided on a positive lens element is designed to exhibit increasingly strong positive refractive powers from center to edge. In the twelfth embodiment, the reduction-side surface of the positive meniscus lens element convex to the enlargement side included in the first lens unit Gr1 is an aspherical surface. This aspherical surface provided oil a positive meniscus lens element is designed to exhibit negative refractive powers in its central portion and positive refractive powers in its peripheral portion.
<The Features of the Third and Fourth Lens Units Gr3 and Gr4>
As noted previously, on the reduction side of the fourth lens unit Gr4 is disposed a dichroic prism PR that performs color synthesis on the light incoming from the liquid crystal panel. Since all of the first to twelfth embodiments are designed primarily as projection optical systems, they need to have a back focal length long enough to secure a space for a dichroic prism PR, and, in addition, they need to be substantially telecentric toward the reduction side so that color shading will be suppressed satisfactorily.
In each embodiment, the third lens unit Gr3 having a negative refractive power and the fourth lens unit Gr4 having a positive refractive power are arranged in such a way that they realize a reversed-telephoto-type arrangement of refractive powers. This makes it possible to secure a sufficiently long back focal length in a projection optical system. Moreover, in each embodiment, a principal ray incident on the third lens unit Gr3 is first refracted by the third lens unit Gr3 to travel away from the optical axis, and is then refracted by the fourth lens unit Gr4 to travel parallel to the optical axis; that is, the entire zoom lens system is designed to be substantially telecentric. This helps reduce color shading and thus improve color rendering at the top, bottom, right, and left edges of the screen.
In the first and some other embodiments, the fourth lens unit Gr4 is constituted of, from the enlargement side, at least one negative lens element and at least two positive lens elements in order to realize a reversed-telephoto-type arrangement of refractive powers as described above in the fourth lens unit Gr4 as well. This makes it possible to secure a sufficiently long back focal length more easily, and to prevent color shading more effectively.
<The Features of the Third Lens Unit Gr3>
�The Refractive Power of the Third Lens Unit Gr3!
To realize a reversed-telephoto-type arrangement of refractive powers, it is preferable that the third lens unit Gr3 satisfy condition (1) below:
0.30<.vertline..PHI.3.vertline..multidot.fS<0.90 (1)
where
.phi.3 represents the refractive power of the third lens unit; and
fS represents the focal length of the entire zoom lens system in the shortest focal length condition.
Condition (1) defines the preferable range of the refractive power of the third lens unit Gr3 with respect to the entire system. If the lower limit of condition (1) is exceeded, it is impossible to secure a back focal length long enough for a projection optical system. By contrast, if the upper limit of condition (1) is exceeded, it is difficult to satisfactorily correct various kinds of aberration (in particular, spherical aberration).
�Three Types of the Third Lens Unit Gr3!
In the first, second, eleventh, and twelfth embodiments, the third lens unit Gr3 has, at its enlargement side end, a meniscus lens element M having a weakly positive refractive power and convex to the enlargement side. In the third, fourth, and seventh to ninth embodiments, the corresponding lens element, i.e. a meniscus lens element M having a negative or weakly positive refractive power and convex to the enlargement side is realized by the use of a doublet lens element formed by joining together a first lens element M1 having a positive refractive power and convex to the enlargement side and a second lens element M2 having a negative refractive power and concave to the reduction side. In the fifth, sixth, and tenth embodiments, the corresponding lens element is realized by the use of separate first and second lens elements M1 and M2, instead of a doublet lens element, and the gap between those two lens elements is used as an air lens.
More specifically, the first to twelfth embodiments of the invention can be classified into the following three types:
Type A: The third lens unit Gr3 has, at its enlargement side end, a single meniscus lens element M having a negative or weakly positive refractive power and convex to the enlargement side (the first, second, eleventh, and twelfth embodiments);
Type B: The third lens unit Gr3 has, at its enlargement side end, a doublet meniscus lens element having a negative or weakly positive refractive power and convex to the enlargement side, and this doublet meniscus lens element is composed by joining together, from the enlargement side, a first lens element M1 having a positive refractive power and convex to the enlargement side and a second lens element M2 having a negative refractive power and concave to the reduction side (the third, fourth, and seventh to ninth embodiments); and
Type C: The third lens unit Gr3 has, from its enlargement side end, a first lens element M1 having a positive refractive power and convex to the enlargement side and a second lens element M2 having a negative refractive power and concave to the reduction side, and the gap between the first and second lens elements M1 and M2 is used as an air lens (the fifth, sixth, and tenth embodiments).
In the type-B embodiments, the doublet lens element composed by joining together the first and second lens elements M1 and M2 has a meniscus shape similar to the meniscus lens element M in the type-A embodiments. In the type-B embodiments, the use of a doublet meniscus lens element that is convex to the enlargement side as a whole contributes to better correction of color-specific distortion and coma aberration than in the type-A embodiments in which a single meniscus lens element M is used. On the other hand, in the type-C embodiments, the use of an air lens contributes to better correction of coma aberration and color-specific image-surface curvature than in the type-A embodiments in which a single meniscus lens element M is used.
�Zooming and Distortion!
An ordinary wide-angle zoom lens system suffers from large negative distortion in the wide-angle condition. In all of the type-A, type-B, and type-C embodiments of the invention, zooming from the telephoto end �L! to the wide-angle end �S! is performed by moving the second and third lens units Gr2 and Gr3 in such a way that the distance between the second and third lens units Gr2 and Gr3 decreases. This means that, as zooming is performed, the positions at which off-axial beams enter the third lens unit Gr3 approach the optical axis (i.e. the heights relative to the optical axis decrease). In addition, the meniscus lens element M of the type-A embodiments and the first and second lens elements M1 and M2 of the type-B and type-C embodiments each have both of their surfaces designed to be convex to the enlargement side. As a result, since the positions at which off-axial beams enter the first and second lens elements M1 and M2 having such surface shapes become closer to the optical axis as the zoom lens system approaches the wide-angle end condition, the negative distortion caused by these surfaces convex to the enlargement side is corrected in such a way that less distortion appears in the wide-angle condition. In this way, the lens element M or lens elements M1 and M2, through the action of their surfaces convex to the enlargement side, serve to reduce the variation of distortion between the telephoto and wide-angle ends.
<The Shape Factor of the Meniscus Lens M>
In the type-A embodiments in which the third lens unit Gr3 satisfies the previously-noted condition (1), it is preferable that the meniscus lens element M satisfy condition (2) below:
3.ltoreq..vertline.(r.sub.MB +r.sub.MA)/(r.sub.MB -r.sub.MA).vertline.(2)
where
r.sub.MB represents the radius of curvature of the enlargement side surface of the meniscus lens element M; and
r.sub.MA represents the radius of curvature of the reduction side surface of the meniscus lens element M.
Condition (2) defines the range of the shape factor of the meniscus lens element M to be preferably satisfied primarily to achieve satisfactory correction of distortion. The meniscus lens element M, as it receives incoming off-axial beams, refracts them on its enlargement side surface convex to the enlargement side in such a way that the beams are directed toward the optical axis, and, as it emits the beams, refracts them on its reduction side surface in such a way that the beams are directed away from the optical axis. As long as the meniscus lens element M satisfies condition (2), the variation of the angles of the incoming off-axial beams and of the angles of the exiting off-axial beams, both with respect to the optical axis, can be kept sufficiently small. As long as the variation of those angles is kept small enough, the meniscus lens element M achieves well-balanced correction of distortion between the telephoto and wide-angle ends without adversely affecting other types of aberration in zoom lens systems of this zooming type.
In condition (2), the radius of curvature r.sub.MA of the enlargement side surface and the radius of curvature r.sub.MB of the reduction side surface of the meniscus lens element M have the same sign. Accordingly, if condition (2) is not satisfied,. the difference .vertline.r.sub.MB, r.sub.MA .vertline. between the radii of curvature of the enlargement and reduction surfaces of the meniscus lens element M is too large, and thus the absolute value of the refractive power of the meniscus lens element M is too large. This means that, if condition (2) is not satisfied, the variation of the angles of the incoming off-axial beams and of the angles of the exiting off-axial beams with respect to the optical axis is so large that it is impossible to achieve well-balanced correction of distortion between the telephoto and wide-angle ends without adversely affecting other types of aberration. Note that, if the radii of curvature r.sub.MA and r.sub.MB are equal, the value of condition (2) .vertline.(r.sub.MB +r.sub.MA)/(r.sub.MB -r.sub.MA).vertline. is infinitely large, and that condition (2) covers also such a case where .vertline.(r.sub.MB +r.sub.MA)/(r.sub.MB -r.sub.MA).vertline. is infinitely large.
�The Surface Shapes of the First and Second Lens Elements M1 and M2!
In the type-B and type-C embodiments in which the third lens unit Gr3 satisfies the previously-noted condition (1), it is preferable that the first and second lens elements M1 and M2 satisfy condition (3) below:
3.ltoreq..vertline.(r.sub.M2B +r.sub.M1A)/(r.sub.M2B -r.sub.M1A)(3)
where
r.sub.M1A represents the radius of curvature of the enlargement side surface of the first lens element M1; and
r.sub.M1B represents the radius of curvature of the reduction side surface of the second lens element M2.
Condition (3) defines the surface shapes, which are equivalent to the shape factors, of the first and second lens elements M1 and M2 to be preferably satisfied primarily to achieve satisfactory correction of distortion. The meniscus lens element M1, as it receives incoming off-axial beams, refracts them on its enlargement side surface convex to the enlargement side in such a way that the beams are directed toward the optical axis, and then the second lens element M2, as it emits the beams, refracts them on its reduction side surface in such a way that the beams are directed away from the optical axis. As long as the first and second lens elements M1 and M2 satisfy condition (3), the variation of the angles of the incoming off-axial beams and of the angles of the exiting off-axial beams, both with respect to the optical axis, can be kept sufficiently small. As long as the variation of those angles is kept small enough, the first and second lens elements M1 and M2 achieve well-balanced correction of distortion between the telephoto and wide-angle ends without adversely affecting other types of aberration in zoom lens systems of this zooming type.
In condition (3), the radius of curvature rM1A of the enlargement side surface of the first lens element M1 and the radius of curvature rM2B of the reduction side surface of the second lens element M2 have the same sign. Accordingly, if condition (3) is not satisfied, the difference .vertline.r.sub.M2B -r.sub.M1A .vertline. between the radii of curvature of the enlargement and reduction surfaces of the first and second lens elements M1 and M2, respectively, is too large, and thus the absolute value of the composite refractive power of the first and second lens elements M1 and M2 is too large. This means that, if condition (3) is not satisfied, the variation of the angles of the incoming off-axial beams and of the angles of the exiting off-axial beams with respect to the optical axis is so large that it is impossible to achieve well-balanced correction of distortion between the telephoto and wide-angle ends without adversely affecting other types of aberration. Note that, if the radii of curvature r.sub.M1A and r.sub.M2B are equal, the value of condition (3) .vertline.(r.sub.M2B +r.sub.M1A)/(r.sub.M2B -r.sub.M1A).vertline. is infinitely large, and that condition (3) covers also such a case where .vertline.(r.sub.M2B +r.sub.M1A)/(r.sub.M2B -r.sub.M1A).vertline. is infinitely large.
�The Air Lens Formed Between the First and Second Lens Elements M1 and M2!
In the type-C embodiments, in which the gap between the first and second lens elements M1 and M2 is used as an air lens, it is preferable that the two lens elements M1 and M2 satisfy conditions (4) and (5) below:
0<d.sub.MIM2 /fS<0.1 (4)
-0.006<(1/r.sub.M2A)-(1/r.sub.M1B)<0.002 (5)
where
d.sub.MIM2 represents the axial aerial distance between the first and second lens elements M1 and M2;
fS represents the focal length of the entire system in the wide-angle-end condition �S!;
r.sub.M1B represents the radius of curvature of the reduction side surface of the first lens element M1; and
r.sub.M2A represents the radius of curvature of the enlargement side surface of the second lens element M2.
Conditions (4) and (5) define the conditions to be satisfied with regard to the air lens formed between the first lens element M1 having a positive refractive power and the second lens element M2 having a negative refractive power. If the upper limit of condition (4) is exceeded, the aerial distance between the first and second lens elements M1 and M2 is too large. If the upper or lower limit of condition (5) is exceeded, the difference between the radii of curvature of the reduction side surface of the first lens element M1 and of the enlargement side surface of the second lens element M2 is too large. In both cases, it is impossible to achieve satisfactory correction of distortion.
�The Abbe Number of the Meniscus Lens Element M!
In the type-A embodiments in which, as in the first and second embodiments, the meniscus lens element M disposed at the enlargement side end of the third lens unit Gr3 is a single meniscus lens element having a positive refractive power, it is preferable that the meniscus lens element M satisfy condition (6) below:
18<.nu..sub.M <30 (6)
where
.nu..sub.M represents the Abbe number of the meniscus lens element M.
Condition (6) defines the range of the Abbe number of the meniscus lens element M having a positive refractive power. If condition (6) is not satisfied, it is impossible to achieve well-balanced correction of lateral chromatic aberration between the wide-angle and telephoto ends.
�The Abbe Numbers of the First and Second Lens Elements M1 and M2!
In the type-B and type-C embodiments, it is preferable that the first and second lens elements M1 and M2 satisfy condition (7) below:
-300<.nu..sub.MIM2 <30 (7)
where
.nu..sub.MIM2 represents the composite Abbe number of the first and second lens elements M1 and M2, which is defined by formula (7A) below:
{1/(f.sub.M1 .multidot..nu..sub.M1)}+{1/(f.sub.M2 .multidot..nu..sub.M2)}={1/(f.sub.M1M2 .multidot..nu..sub.M1M2)}(7A)
where
f.sub.M1 represents the focal length of the first lens element M1;
f.sub.M2 represents the focal length of the second lens element M2;
f.sub.M1M2 represents the composite focal length of the first and second lens elements M1 and M2;
.nu..sub.M1 represents the Abbe number of the first lens element M1; and
.nu..sub.M2 represents the Abbe number of the second lens element M2.
Condition (7) defines the ranges of the Abbe numbers of the first and second lens elements M1 and M2. If condition (7) is not satisfied, just as when condition (6) is not satisfied, it is impossible to achieve well-balanced correction of lateral chromatic aberration between the wide-angle and telephoto ends.
�The Refractive Indices of the First and Second Lens Elements M1 and M2!
In the type-B and type-C embodiments, it is preferable that the first and second lens elements M1 and M2 satisfy condition (8) below:
0.85<n.sub.M2 /n.sub.M1 <0.95 (8)
where
n.sub.M1 represents the refractive index of the first lens element M1; and
n.sub.M2 represents the refractive index of the second lens element M2.
Condition (8) defines the ranges of the refractive indices of the first and second lens elements M1 and M2. If the refractive indices n.sub.M1 and n.sub.M2 of the first and second lens elements M1 and M2 are equal, then n.sub.M2 /n.sub.M1 =1, which means that the first and second lens elements M1 and M2, as a whole, act in the same manner as the single meniscus lens element M in the type-A embodiments. Accordingly, if the upper limit of the condition (8) is exceeded, the first and second lens elements M1 and M2, as a whole, behave more like a single meniscus lens element. As a result, the previously described effect of using two lens elements M1 and M2 to compose the single meniscus lens element convex to the enlargement side as a whole becomes less noticeable. By contrast, if the lower limit of condition (8) is exceeded, the variation of color-specific spherical aberration and coma aberration during zooming is too large, and thus it is impossible to obtain satisfactory optical performance. Since, as described previously, the positions at which off-axial beams enter the third lens unit Gr3 vary with zooming, it is possible to obtain well-balanced image planes over the entire zoom range by setting the difference between the refractive indices of the first and second lens elements M1 and M2 to a value that satisfies condition (8).
<The Features of the First Lens Unit Gr1>
In the type-A, type-B, and type-C embodiments in which the previously-noted condition (1) as well as (2) or (3) is satisfied, it is preferable that the first lens unit Gr1 consist of at least two negative lens elements and at least one positive lens element. By constituting the first lens unit Gr1 in that manner, it is possible to reduce under-side distortion caused by the light beams incident on the peripheral portion of the first lens unit Gr1 that has a negative power in the wide-angle condition. This is because, by distributing the negative power of the first lens unit Gr1 between two lens elements, it is possible to reduce the angles of rays with respect to the lens surfaces, and thus to reduce the negative distortion that is mostly caused by the negative lens elements of the first lens unit Gr1. This makes it easier to correct distortion, for example, by means of the positive lens element of the first lens unit Gr1.
�The Aspherical Surface in the First Lens Unit Gr1!
In the type-A, type-B, and type-C embodiments in which the previously-noted condition (1) as well as (2) or (3) is satisfied, it is preferable, as in the eleventh embodiment, that an aspherical surface having increasingly strong positive refractive powers from center to edge be provided on at least one surface having a positive refractive power within the first lens unit Gr1. By providing such an aspherical surface in the first lens unit Gr1, the under-side distortion caused by the negative lens elements can more effectively be corrected toward the over side, in particular in the wide-angle condition �S!.
In the type-A, type-B, and type-C embodiments in which the previously-noted condition (1) as well as (2) or (3) is satisfied, it is also possible, as in the twelfth embodiment, to provide an aspherical surface having negative refractive powers at the center and positive refractive powers at the edge on at least one surface having a weakly negative refractive power within the first lens unit Gr1. By providing such an aspherical surface in the first lens unit Gr1, just as when an aspherical surface as described in the previous paragraph is provided, the under-side distortion caused by the negative lens elements can more effectively be corrected toward the over side, in particular in the wide-angle condition �S!.
It is preferable that the aspherical surface as described above be provided on a positive lens element within the first lens unit Gr1. When the aspherical surface is provided on a positive lens element, it is preferable that the positive lens element satisfy condition (9) below:
1.45<na<1.60 (9)
where
na represents the refractive index of the positive lens element on which the aspherical surface is provided.
Condition (9) defines the refractive index of the positive lens element on which the aspherical surface is provided. The positive lens element provided with the aspherical surface corrects distortion as described above more effectively if it is made of a medium having a refractive index low enough to satisfy condition (9). Note that it is also possible to achieve similar correction of distortion by making the negative lens element in the first lens unit Gr1 of a medium having such a high refractive index as exceeds the upper limit of condition (9) and providing it with an aspherical surface having a quite contrary shape. However, providing an aspherical surface on a medium having a high refractive index is undesirable, because it demands extra cost.
<The Features of the Second Lens Unit Gr2>
In the type-A, type-B, and type-C embodiments in which the previously-noted condition (1) as well as (2) or (3) is satisfied it is preferable, as in the second and the eighth to tenth embodiments, that the second lens unit Gr2 consist of, from the enlargement side, a meniscus lens element convex to the enlargement side and having a negative refractive power, and a doublet lens element having a positive refractive power as a whole. By constituting the second lens unit Gr2 in that manner, it is possible to correct coma aberration by means of the air lens formed between the negative meniscus lens element and the positive doublet lens element mentioned above. This is because, owing to the difference of the curvature between the surfaces on both sides of the gap between the meniscus lens element and the doublet lens element, marginal rays entering the second lens unit Gr2 are refracted by the meniscus lens element in such a way that the rays are directed away from the optical axis, and thus the rays enter the doublet lens element with large incident angles. In this way, the air gap between these lens elements effectively serves to correct coma aberration.
<The Refractive Powers of the First and Second Lens Units Gr1 and Gr2>
In the type-A, type-B, and type-C embodiments in which the previously-noted condition (1) as well as (2) or (3) is satisfied and in which zooming is performed by moving the first and second lens units Gr1 and Gr2, it is desirable that condition (10) below be satisfied:
0.50<.vertline..phi.1.vertline./.phi.2<0.75 (10)
where
.phi.1 represents the refractive power of the first lens unit Gr1; and
.phi.2 represents the refractive power of the second lens unit Gr2.
Condition (10) defines the relation between the refractive powers of the first and second lens units Gr1 and Gr2 (in particular, the condition to be satisfied with regard to the loci of the lens units that are moved during zooming). As the value of condition (10) is closer to its upper limit, the first lens unit Gr1 needs to be positioned farther to the enlargement side in the telephoto end condition �L! than in the wide-angle end condition �S!. As a result, the length of the entire zoom lens system in the telephoto end condition �L! becomes so large that it is impossible to realize a compact zoom lens system. By contrast, as the value of condition (10) is closer to its lower limit, the first lens unit Gr1 needs to be positioned farther to the reduction side ill the telephoto end condition �L! than in the wide-angle end condition �S!. As a result, it is impossible to secure sufficient brightness of the edge of the image field in the wide-angle end condition �S!. This can be avoided by designing the first and second lens units Gr1 and Gr2 to have larger lens diameters, but doing so makes it impossible to realize a compact zoom lens system.
<The Features of the Fourth Lens Unit Gr4>
�The Refractive Power of the Fourth Lens Unit Gr4!
In the type-A, type-B, and type-C embodiments in which the previously-noted condition (1) as well as (2) or (3) is satisfied, it is preferable that condition (11) below be satisfied:
0.65<.phi.4.multidot.fS<1.3 (11)
where
.phi.4 represents the refractive power of the fourth lens unit Gr4; and
fS represents the focal length of the entire system in the wide-angle end condition �S!.
Condition (11) defines the range of the refractive power of the fourth lens unit Gr4 with respect to the entire system. If the upper limit of condition (11) is exceeded, too large spherical and coma aberration appears, and thus it is impossible to reduce the f-number sufficiently. As a result, it is difficult to obtain sufficiently bright images through the zoom lens system. By contrast, if the lower limit of condition (11) is exceeded, it is impossible to secure a back focal length long enough for a projection optical system.
�The Position of the Fourth Lens Unit Gr4 During Zooming!
In the type-A, type-B, and type-C embodiments in which the previously-noted condition (1) as well as (2) or (3) is satisfied, it is preferable that the fourth lens unit Gr4 be kept in a fixed position during zooming. This makes it possible to fix the position of a large-size component (e.g. a dichroic prism PR disposed on the reduction side of the fourth lens unit Gr4) that is required in a projection optical system, and thus provides various advantages in the design of the lens barrel. For example, the structure of the lens barrel can be simplified, and therefore cost reduction can be achieved easily.
<<Embodiments 13 to 21>>
The thirteenth to twenty-first embodiments are three-unit zoom lens systems each constituted of, from the enlargement side, a first lens unit Gr1 having a negative refractive power, a second lens unit Gr2 having a positive refractive power, and a third lens unit Gr3 having a positive refractive power. In addition, a dichroic prism PR is disposed on the reduction side of the third lens unit Gr3. All of these zoom lens systems perform zooming by varying the distances between the first to third lens units Gr1 to Gr3; specifically, during zooming from the wide-angle end �S !to the telephoto end �L!, the second lens unit Gr2 is moved along the optical axis in such a way that the distance between the second and third lens units Gr2 and Gr3 increases. The third lens unit Gr3 consists of, from the enlargement side, a front lens subunit GrF having a negative refractive power and a rear lens subunit GrR having a positive refractive power. The front lens subunit GrF includes at least one negative lens element, and the rear lens subunit GrR includes at least two positive lens elements. The constitution of the first to third lens units Gr1 to Gr3 in each embodiment will be described in more detail below.
<The Constitution of the First Lens Unit Gr1>
In the thirteenth, fourteenth, and nineteenth embodiments, the first lens unit Gr1 consists of, from the enlargement side, a negative meniscus lens element concave to the reduction side, a negative biconcave lens element, and a positive meniscus lens element convex to the enlargement side. In the fifteenth embodiment, the first lens unit Gr1 consists of, from the enlargement side, a negative meniscus lens element concave to the reduction side, and a positive meniscus lens element convex to the enlargement side. In the sixteenth to eighteenth embodiments, the first lens unit Gr1 consists of, from the enlargement side, a negative meniscus lens element concave to the reduction side, a positive meniscus lens element convex to the enlargement side, and a negative meniscus lens element concave to the reduction side. In the twentieth embodiment, the first lens unit Gr1 consists of, from the enlargement side, a negative meniscus lens element concave to the reduction side, and a positive biconvex lens element. In the twenty-first embodiment, the first lens unit Gr1 consists of, from the enlargement side, two negative meniscus lens elements both concave to the reduction side, and a positive meniscus lens element convex to the enlargement side.
<The Constitution of the Second Lens Unit Gr2>
In the thirteenth and nineteenth embodiments, the second lens unit Gr3 consists of, from the enlargement side, a positive biconvex lens element, and a doublet lens element formed by joining together a negative meniscus lens element concave to the reduction side and a positive biconvex lens element. In the fourteenth embodiment, the second lens unit Gr2 consists of, from the enlargement side, a positive biconvex lens element, and a doublet lens element formed by joining together a positive biconvex lens element and a negative meniscus lens element concave to the enlargement side. In the fifteenth and twenty-first embodiments, the second lens unit Gr2 consists of, from the enlargement side, a positive meniscus lens element convex to the enlargement side, a negative meniscus lens element concave to the reduction side, and a positive biconvex lens element. In the sixteenth to eighteenth, and twentieth embodiments, the second lens unit Gr2 consists of, from the enlargement side, a positive biconvex lens element, a negative meniscus lens element concave to the reduction side, and a positive biconvex lens element.
<The Constitution of the Front Lens Subunit GrF of the Third Lens Unit Gr3>
In the thirteenth embodiment, the front lens subunit GrF of the third lens unit Gr3 consists of, from the enlargement side, a positive meniscus lens element M convex to the enlargement side, and two negative meniscus lens elements both concave to the reduction side. In the fourteenth embodiment, the front lens subunit GrF of the third lens unit Gr3 consists of, from the enlargement side, a positive meniscus lens element convex to the enlargement side, and a negative biconcave lens element. In the fifteenth and sixteenth embodiments, the front lens subunit GrF of the third lens unit Gr3 consists of, from the enlargement side, a negative meniscus lens element M convex to the enlargement side, and a negative biconcave lens element. In the seventeenth and twenty-first embodiments, the front lens subunit GrF of the third lens unit Gr3 consists of, from the enlargement side, a doublet lens element formed by joining together a positive meniscus lens element M1 convex to the enlargement side and a negative meniscus lens element M2 concave to the reduction side, and a negative biconcave lens element. In the eighteenth, nineteenth, and twentieth embodiments, the front lens subunit GrF of the third lens unit Gr3 consists of, from the enlargement side, a positive meniscus lens element M1 convex to the enlargement side, a negative meniscus lens element M2 concave to the reduction side, and a negative biconcave lens element.
<The Constitution of the Rear Lens Subunit GrR of the Third Lens Unit Gr3>
In the thirteenth embodiment, the rear lens subunit GrR of the third lens unit Gr3 consists of, from the enlargement side, two positive meniscus lens elements both convex to the reduction side, and a positive meniscus lens element convex to the enlargement side. In the fourteenth and fifteenth embodiments, the rear lens subunit GrR of the third lens unit Gr3 consists of, from the enlargement side, a doublet lens element formed by joining together a negative meniscus lens element concave to the reduction side and a positive biconvex lens element, and a positive biconvex lens element. In the sixteenth and seventeenth embodiments, the rear lens subunit GrR of the third lens unit Gr3 consists of, from the enlargement side, a doublet lens element formed by joining together a negative meniscus lens element concave to the reduction side and a positive biconvex lens element, and two positive biconvex lens elements. In the eighteenth, nineteenth, and twenty-first embodiments, the rear lens subunit GrR of the third lens unit Gr3 consists of, from the enlargement side, a positive meniscus lens element convex to the reduction side, a positive biconvex lens element, and a positive meniscus lens element convex to the enlargement side. In the twentieth embodiment, the rear lens subunit GrR of the third lens unit Gr3 consists of, from the enlargement side, two positive biconvex lens elements, and a positive meniscus lens element convex to the enlargement side.
<Aspherical Surface>
In the twentieth embodiment, the reduction-side surface of the positive biconvex lens element included in the first lens unit Gr1 and the reduction-side surface of the negative biconcave lens element included in the third lens unit Gr3 are aspherical surfaces. The aspherical surface provided on the reduction-side surface of the positive biconvex lens element of the first lens unit Gr1 is designed to exhibit increasingly strong positive refractive powers from center to edge. In the twenty-first embodiment, the reduction-side surface of the positive meniscus lens element convex to the enlargement side included in the first lens unit Gr1 is an aspherical surface.
This aspherical surface provided on a positive meniscus lens element is designed to exhibit negative refractive powers in its central portion and positive refractive powers in its peripheral portion.
<The Features of the Third Lens Unit Gr3>
As noted previously, on the reduction side of the third lens unit Gr3 is disposed a dichroic prism PR that performs color synthesis on the light incoming from the liquid crystal panel. Since all of the thirteenth to twenty-first embodiments are designed primarily as projection optical systems, they need to have a back focal length long enough to secure a space for a dichroic prism PR, and, in addition, they need to be substantially telecentric toward the reduction side so that color shading will be suppressed satisfactorily.
In each embodiment, the front lens subunit GrF having a negative refractive power and the rear lens subunit GrR having a positive refractive power of the third lens unit Gr3 are arranged in such a way that they realize a reversed-telephoto-type arrangement of refractive powers. This makes it possible to secure a sufficiently long back focal length in a projection optical system. Moreover, in each embodiment, a principal ray incident on the third lens unit Gr3 is first refracted by the front lens subunit GrF to travel away from the optical axis, and is then refracted by the rear lens subunit GrR to travel parallel to the optical axis; that is, the entire zoom lens system is designed to be substantially telecentric. This helps reduce color shading and thus improve color rendering at the top, bottom, right, and left edges of the screen.
�The Refractive Power of the Front Lens Subunit GrF!
In a reversed-telephoto-type arrangement of refractive powers as described above, it is preferable that the front lens subunit GrF of the third lens unit Gr3 satisfy condition (12) below:
0.80<.vertline..phi.F.vertline..multidot.fS<1.30 (12)
where
.phi.F represents the refractive power of the front lens subunit GrF; and
fS represents the focal length of the entire system in the wide-angle end condition �S!.
Condition (12) defines the range of the refractive power of the front lens subunit GrF with respect to the entire system. If the lower limit of condition (12) is exceeded, it is impossible to secure a back focal length long enough for a projection optical system. By contrast, if the upper limit of condition (12) is exceeded, it is difficult to satisfactorily correct various kinds of aberration (in particular, spherical aberration).
�Three Types of the Front Lens Subunit GrF!
In the thirteenth to sixteenth embodiments, the front lens subunit GrF of the third lens unit Gr3 has, at its enlargement side end, a meniscus lens element M having a negative or weakly positive refractive power and convex to the enlargement side. In the seventeenth and twenty-first embodiments, the corresponding lens element is realized by the use of a doublet lens element formed by joining together a first lens element M1 having a positive refractive power and convex to the enlargement side and a second lens element M2 having a negative refractive power and concave to the reduction side. In the eighteenth to twentieth embodiments, the corresponding lens element is realized by the use of separate first and second lens elements M1 and M2, instead of a doublet lens element, and the gap between those two lens elements is used as an air lens.
More specifically, the thirteenth to twenty-first embodiments of the invention can be classified into the following three types:
Type D: The front lens subunit GrF has,. at its enlargement side end, a single meniscus lens element M having a negative or weakly positive refractive power and convex to the enlargement side (the thirteenth to sixteenth embodiments);
Type E: The front lens subunit GrF has, at its enlargement side end, a doublet meniscus lens element having a negative or weakly positive refractive power and convex to the enlargement side, and this doublet meniscus lens element is composed by joining together, from the enlargement side, a first lens element M1 having a positive refractive power and convex to the enlargement side and a second lens element M2 having a negative refractive power and concave to the reduction side (the seventeenth and twenty-first embodiments); and
Type F: The front lens subunit GrF has, from its enlargement side end, a first lens element M1 having a positive refractive power and convex to the enlargement side and a second lens element M2 having a negative refractive power and concave to the reduction side, and the gap between the first and second lens elements M1 and M2 is used as an air lens (the eighteenth to twentieth embodiments).
In the type-E embodiments, the doublet lens element composed by joining together the first and second lens elements M1 and M2 has a meniscus shape similar to the meniscus lens element M in the type-D embodiments. In the type-E embodiments, the use of a doublet meniscus lens element that is convex to the enlargement side as a whole contributes to better correction of color-specific distortion and coma aberration than in the type-D embodiments in which a single meniscus lens element M is used. On the other hand, in the type-F embodiments, the use of an air lens contributes to better correction of coma aberration and color-specific image-surface curvature than in the type-D embodiments in which a single meniscus lens element M is used.
�Zooming and Distortion!
An ordinary wide-angle zoom lens system suffers from large negative distortion in the wide-angle condition. In all of the type-D, type-E, and type-F embodiments of the invention, zooming from the telephoto end �L! to the wide-angle end �S! is performed by moving the second lens unit Gr2 in such a way that the distance between the second and third lens units Gr2 and Gr3 decreases. This means that, as zooming is performed, the positions at which off-axial beams enter the third lens unit Gr3 approach the optical axis (i.e. the heights relative to the optical axis decrease). In addition, the meniscus lens element M of the type-D embodiments and the first and second lens elements M1 and M2 of the type-E and type-F embodiments each have both of their surfaces designed to be convex to the enlargement side. As a result, since the positions at which off-axial beams enter the first and second lens elements M1 and M2 having such surface shapes become closer to the optical axis as the zoom lens system approaches the wide-angle end condition, the negative distortion caused by these surfaces convex to the enlargement side is corrected in such a way that less distortion appears in the wide-angle condition. In this way, the lens element M or lens elements M1 and M2, through the action of their surfaces convex to the enlargement side, serve to reduce the variation of distortion between the telephoto and wide-angle ends.
<The Shape Factor of the Meniscus Lens M>
In the type-D embodiments in which the front lens subunit GrF satisfies the previously-noted condition (12), it is preferable that the meniscus lens element M satisfy condition (2) introduced earlier.
Condition (2) defines the range of the shape factor of the meniscus lens element M to be preferably satisfied primarily to achieve satisfactory correction of distortion. The meniscus lens element M, as it receives incoming off-axial beams, refracts them on its enlargement side surface convex to the enlargement side in such a way that the beams are directed toward the optical axis, and, as it emits the beams, refracts them on its reduction side surface in such a way that the beams are directed away from the optical axis. As long as the meniscus lens element M satisfies condition (2), the variation of the angles of the incoming off-axial beams and of the angles of the exiting off-axial beams, both with respect to the optical axis, can be kept sufficiently small. As long as the variation of those angles is kept small enough, the meniscus lens element M achieves well-balanced correction of distortion between the telephoto and wide-angle ends without adversely affecting other types of aberration in zoom lens systems of this zooming type.
In condition (2), the radius of curvature r.sub.MA of the enlargement side surface and the radius of curvature r.sub.MB of the reduction side surface of the meniscus lens element M have the same sign. Accordingly, if condition (2) is not satisfied, the difference .vertline.r.sub.MB -r.sub.MA .vertline. between the radii of curvature of the enlargement and reduction surfaces of the meniscus lens element M is too large, and thus the absolute value of the refractive power of the meniscus lens element M is too large. This means that, if condition (2) is not satisfied, the variation of the angles of the incoming off-axial beams and of the angles of the exiting off-axial beams with respect to the optical axis is so large that it is impossible to achieve well-balanced correction of distortion between the telephoto and wide-angle ends without adversely affecting other types of aberration. Note that, if the radii of curvature r.sub.MA and r.sub.MB are equal, the value of condition (2) .vertline.(r.sub.MB +r.sub.MA)/(r.sub.MB -r.sub.MA).vertline. is infinitely large, and that condition (2) covers also such a case where (r.sub.MB +r.sub.MA)/(r.sub.MB -r.sub.MA).vertline. is infinitely large.
�The Surface Shapes of the First and Second Lens Elements M1 and M2!
In the type-E and type-F embodiments in which the front lens subunit GrF satisfies the previously-noted condition (12), it is preferable that the first and second lens elements M1 and M2 satisfy condition (3) introduced earlier.
Condition (3) defines the surface shapes, which are equivalent to the shape factors, of the first and second lens elements M1 and M2 to be preferably satisfied primarily to achieve satisfactory correction of distortion. The meniscus lens element M1, as it receives incoming off-axial beams, refracts them on its enlargement side surface convex to the enlargement side in such a way that the beams are directed toward the optical axis, and then the second lens element M2, as it emits the beams. refracts them on its reduction side surface in such a way that the beams are directed away from the optical axis. As long as the first and second lens elements M1 and M2 satisfy condition (3), the variation of the angles of the incoming off-axial beams and of the angles of the exiting off-axial beams, both with respect to the optical axis, can be kept sufficiently small. As long as the variation of those angles is kept small enough, the first and second lens elements M1 and M2 achieve well-balanced correction of distortion between the telephoto and wide-angle ends without adversely affecting other types of aberration in zoom lens systems of this zooming type.
In condition (3), the radius of curvature r.sub.M1A of the enlargement side surface of the first lens element M1 and the radius of curvature r.sub.M2B of the reduction side surface of the second lens element M2 have the same sign. Accordingly, if condition (3) is not satisfied, the difference .vertline.r.sub.M2B -r.sub.M1A .vertline. between the radii of curvature of the enlargement and reduction surfaces of the first and second lens elements M1 and M2, respectively, is too large, and thus the absolute value of the composite refractive power of the first and second lens elements M1 and M2 is too large. This means that, if condition (3) is not satisfied, the variation of the angles of the incoming off-axial beams and of the angles of the exiting off-axial beams with respect to the optical axis is so large that it is impossible to achieve well-balanced correction of distortion between the telephoto and wide-angle ends without adversely affecting other types of aberration. Note that, if the radii of curvature r.sub.M1A and r.sub.M2B are equal, the value of condition (3) .vertline.(r.sub.M2B +r.sub.M1A)/(r.sub.M2B -r.sub.M1A).vertline. is infinitely large, and that condition (3) covers also such a case where .vertline.(r.sub.M2B +r.sub.M1A)/(r.sub.M2B -r.sub.M1A).vertline. is infinitely large.
�The Air Lens Formed Between the First and Second Lens Elements M1 and M2!
In the type-F embodiments, in which the gap between the first and second lens elements M1 and M2 is used as an air lens, it is preferable that the two lens elements M1 and M2 satisfy conditions (4) and (5) introduced earlier.
Conditions (4) and (5) define the conditions to be satisfied with regard to the air lens formed between the first lens element M1 having a positive refractive power and the second lens element M2 having a negative refractive power. If the upper limit of condition (4) is exceeded, the aerial distance between the first and second lens elements M1 and M2 is too large. If the upper or lower limit of condition (5) is exceeded, the difference between the radii of curvature of the reduction side surface of the first lens element M1 and of the enlargement side surface of the second lens element M2 is too large. In both cases, it is impossible to achieve satisfactory correction of distortion.
�The Abbe Number of the Meniscus Lens Element M!
In the type-D embodiments in which, as in the thirteenth and fourteenth embodiments, the meniscus lens element M disposed at the enlargement side end of the front lens subunit GrF is a single meniscus lens element having a positive refractive power, it is preferable that the meniscus lens element M satisfy condition (6) introduced earlier.
Condition (6) defines the range of the Abbe number of the meniscus lens element M having a positive refractive power. If condition (6) is not satisfied, it is impossible to achieve well-balanced correction of lateral chromatic aberration between the wide-angle and telephoto ends.
�The Abbe Numbers of the First and Second Lens Elements M1 and M2!
In the type-E and type-F embodiments, it is preferable that the first and second lens elements M1 and M2 satisfy condition (7) introduced earlier.
Condition (7) defines the ranges of the Abbe numbers of the first and second lens elements M1 and M2. If condition (7) is not satisfied, just as when condition (6) is not satisfied, it is impossible to achieve well-balanced correction of lateral chromatic aberration between the wide-angle and telephoto ends.
�The Position of the Third Lens Unit Gr3 During Zooming!
In the type-D, type-E, and type-F embodiments in which the previously-noted condition (12) as well as (2) or (3) is satisfied, it is preferable that the third lens unit Gr3 be kept in a fixed position during zooming. This makes it possible to fix the position of a large-size component (e.g. a dichroic prism PR disposed on the reduction side of the third lens unit Gr3) that is required in a projection optical system, and thus provides various advantages in the design of the lens barrel. For example, the structure of the lens barrel can be simplified, and therefore cost reduction can be achieved easily. ps �The Refractive Power of the Third Lens Unit Gr3!
In the type-D, type-E, and type-F embodiments in which the previously-noted condition (12) as well as (2) or (3) is satisfied, it is preferable that condition (13) below be satisfied:
0.40<.phi.3.multidot.fS<0.70 (13)
where
.phi.3 represents the refractive power of the third lens unit Gr3; and
fS represents the focal length of the entire system in the wide-angle end condition �S!.
Condition (13) defines the range of the refractive power of the third lens unit Gr3 with respect to the entire system. If the upper limit of condition (13) is exceeded. too large aberration (in particular, spherical and coma aberration) appears, and thus it is impossible to reduce the f-number sufficiently. As a result, it is difficult to obtain sufficiently bright images through the zoom lens system. By contrast, if the lower limit of condition (13) is exceeded, the refractive power of the third lens unit Gr3 is too weak, with the result that, to secure a comparably wide zoom range, the first and second lens units Gr1 and Gr2 need to be moved longer distances. Thus, it is impossible to realize a compact zoom lens system.
<The Refractive Powers of the First and Second Lens Units Gr1 and Gr2>
In the type-D, type-E, and type-F embodiments in which the previously-noted condition (12) as well as (2) or (3) is satisfied and in which zooming is performed by moving the first and second lens units Gr1 and Gr2, it is desirable that condition (10) introduced earlier be satisfied.
Condition (10) defines the relation between the refractive powers of the first and second lens units Gr1 and Gr2 (in particular, the condition to be satisfied with regard to the loci of the lens units that are moved during zooming). As the value of condition (10) is closer to its upper limit, the first lens unit Gr1 needs to be positioned farther to the enlargement side in the telephoto end condition �L! than in the wide-angle end condition �S!. As a result, the length of the entire zoom lens system in the telephoto end condition �L! becomes so large that it is impossible to realize a compact zoom lens system. By contrast, as the value of condition (10) is closer to its lower limit, the first lens unit Gr1 needs to be positioned farther to the reduction side in the telephoto end condition �L! than in the wide-angle end condition �S!. As a result, it is impossible to secure sufficient brightness of the edge of the image field in the wide-angle end condition �S!. This can be avoided by designing the first and second lens units Gr1 and Gr2 to have larger lens diameters, but doing so makes it impossible to realize a compact zoom lens system.
<The Features of the First Lens Unit Gr1>
In the type-D, type-E, and type-F embodiments in which the previously-noted condition (12) as well as (2) or (3) is satisfied, it is preferable that the first lens unit Gr1 consist of at least two negative lens elements and at least one positive lens element. By constituting the first lens unit Gr1 in that manner, it is possible to reduce under-side distortion caused by the light beams incident on the peripheral portion of the first lens unit Gr1 that has a negative power in the wide-angle condition. This is because, by distributing the negative power of the first lens unit Gr1 between two lens elements, it is possible to reduce the angles of rays with respect to the lens surfaces, and thus to reduce the negative distortion that is mostly caused by the negative lens elements of the first lens unit Gr1. This makes it easier to correct distortion, for example, by means of the positive lens element of the first lens unit Gr1.
�The Aspherical Surface in the First Lens Unit Gr1!
In the type-D, type-E, and type-F embodiments in which the previously-noted condition (12) as well as (2) or (3) is satisfied, it is preferable, as in the twentieth embodiment, that an aspherical surface having increasingly strong positive refractive powers from center to edge be provided on at least one surface having a positive refractive power within the first lens unit Gr1. By providing such an aspherical surface in the first lens unit Gr1, the under-side distortion caused by the negative lens elements can more effectively be corrected toward the over side, in particular in the wide-angle condition �S!.
In the type-D, type-E, and type-F embodiments in which the previously-noted condition (12) as well as (2) or (3) is satisfied, it is also possible, as in the twenty-first embodiment, to provide an aspherical surface having negative refractive powers at the center and positive refractive powers at the edge on at least one surface having a weakly negative refractive power within the first lens unit Gr1. By providing such an aspherical surface in the first lens unit Gr1, just as when an aspherical surface as described in the previous paragraph is provided, the under-side distortion caused by the negative lens elements can more effectively be corrected toward the over side, in particular in the wide-angle condition �S!.
It is preferable that the aspherical surface as described above be provided on a positive lens element within the first lens unit Gr1. When the aspherical surface is provided on a positive lens element, it is preferable that the positive lens element satisfy condition (9) introduced earlier.
Condition (9) defines the refractive index of the positive lens element on which the aspherical surface is provided. The positive lens element provided with the aspherical surface corrects distortion as described above more effectively if it is made of a medium having a refractive index low enough to satisfy condition (9). Note that it is also possible to achieve similar correction of distortion by making the negative lens element in the first lens unit Gr1 of a medium having such a high refractive index as exceeds the upper limit of condition (9) and providing it with an aspherical surface having a quite contrary shape. However, providing an aspherical surface on a medium having a high refractive index is undesirable, because it demands extra cost.
<<Examples of the First to Twenty-first Embodiments>>
Tables 1 to 21 respectively list the construction data of examples of the zoom lens systems of the first to twenty-first embodiments (FIGS. 1A-1C, 3A-3C, 5A-5C, 7A-7C, 9A-9C, 11A-11C, 13A-13C, 15A-15C, 17A-17C, 19A-19C, 21A-21C, 23A-23C, 25A-25C, 27A-27C, 29A-29C, 31A-31C, 33A-33C, 35A-35C, 37A-37C, 39A-39C, and 41A-41C).
In the construction data of each embodiment, ri (i=1, 2, 3, . . . ) represents the radius of curvature of the i-th surface from the enlargement side, di (i=1, 2, 3, . . . ) represents the i-th axial distance from the enlargement side, and Ni (i=1, 2, 3, . . . ) and vi (i=1, 2, 3, . . . ) respectively represent the refractive index (Nd) and the Abbe number (.nu.d), for the d line, of the i-th lens element from the enlargement side. Moreover, for each of such axial distances as vary with zooming (variable axial distances), three values are given that are, from the left, the axial distance in the telephoto end condition (longest-focal-length condition) �L!, the axial distance in the middle condition (middle-focal-length condition) �M!, and the axial distance in the wide-angle end condition (shortest-focal-length condition) �S!. Also listed for each embodiment are the focal length f and the f-number FNO of the entire system in each of these three focal-length conditions �L!, �M!, and �S!.
In the construction data of each embodiment, a surface marked with an asterisk (*) is an aspherical surface, whose surface shape is defined by formula (AS) below: ##EQU1## where X represents the displacement from the reference surface in the optical axis direction;
Y represents the height in a direction perpendicular to the optical axis;
C represents the paraxial curvature;
.epsilon. represents the quadric surface parameter; and
Ai represents the aspherical coefficient of i-th order.
Tables 22 to 24 list the values corresponding to conditions (1) to (11) as observed in the examples of the first to twelfth embodiments; specifically, for each embodiment, Table 22 lists the values of .vertline..phi.3.vertline..multidot.fS (condition (1)), .vertline.(r.sub.MB +r.sub.MA)/(r.sub.MB -r.sub.MA).vertline. (condition (2)), .vertline.(r.sub.M2B +r.sub.M1A)/(r.sub.M2B -r.sub.M1A).vertline. (condition (3)), and d.sub.M1M2 /fS (condition (4)); Table 23 lists the values of (1/r.sub.M2A)-(1/r.sub.M1B) (condition (5)), .nu..sub.M (condition (6)), .nu..sub.M1M2 (condition (7)), and n.sub.M2 /n.sub.M1 (condition (8)); and Table 24 lists the values of na (condition (9)), .vertline..phi.1.vertline./.phi.2 (condition (10)), and .phi.4.multidot.fS (condition (11)).
Tables 25 and 26 list the values corresponding to conditions (2) to (7), (9), (10), (12), and (13) as observed in the examples of the thirteenth to twenty-first embodiments; specifically, for each embodiment, Table 25 lists the values of .vertline..phi.F.vertline..multidot.fS (condition (12)), (r.sub.MB +r.sub.MA)/(r.sub.MB -r.sub.MA).vertline. (condition (2)), (r.sub.M2B +r.sub.M1A)/(r.sub.M2B -r.sub.M1A).vertline. (condition (3)), d.sub.M1M2 /fS (condition (4)), (1/r.sub.M2A)-(1/r.sub.M1B) (condition (5)); and Table 26 lists the values of .nu..sub.M (condition (6)), .nu..sub.M1M2 (condition (7)), .phi.3.multidot.fS (condition (13)), .vertline..phi.1.vertline./.phi.2 (condition (10)), and na (condition (9)).
These examples of the first to twenty-first embodiments (each as an optical system including a dichroic prism PR) exhibit aberrations as shown in FIGS. 2A-2I, 4A-4I, 6A-6I, 8A-8I, 10A-10I, 12A-12I, 14A-14I, 16A-16I, 18A-18I, 20A-20I, 22A-22I, 24A-24I, 26A-26I, 28A-28I, 30A-30I, 32A-32I, 34A-34I, 36A-36I, 38A-38I, 40A-40I, and 42A-42I, respectively. Of these aberration diagrams. FIGS. 2A-2C, 4A-4C, 6A-6C, 8A-8C, 10A-10C, 12A-12C, 14A-14C, 16A-16C, 18A-18C, 20A-20C, 22A-22C, 24A-24C, 26A-26C, 28A-28C, 30A-30C, 32A-32C, 34A-34C, 36A-36C, 38A-38C, 40A-40C, and 42A-42C show three relevant types of aberration as observed in the longest-focal-length condition �L!, FIGS. 2D-2F, 4D-4F, 6D-6F, 8D-8F, 10D-10F, 12D-12F, 14D-14F, 16D-16F, 18D-18F, 20D-20F, 22D-22F, 24D-24F, 26D-26F, 28D-28F, 30D-30F, 32D-32F, 34D-34F, 36D-36F, 38D-38F, 40D-40F, and 42D-42F show the same types of aberration as observed in the middle-focal-length condition �M!, and FIGS. 2G-2I, 4G-4I, 6G-6I, 8G-8I, 10G-10I, 12G-12I, 14G-14I, 16G-16I, 18G-18I, 20G-20I, 22G-22I, 24G-24I. 26G-26I, 28G-28I, 30G-30I, 32G-32I, 34G-34I, 36G-36I, 38G-38I, 40G-40I, and 42G-42I show the same types of aberration as observed in the shortest-focal-length condition �S!. In these aberration diagrams, Y' represents the image height; a solid line (d) indicates the aberration for the d line, and a dash-dot line (g) indicates the aberration for the g line; a broken line (DM) and a solid line (DS) respectively represent the astigmatism for the d line on the meridional and sagittal planes, respectively.
In practical use as a projection optical system for a liquid crystal projector, the zoom lens systems of the embodiments have the image plane on the screen, and the surface of the liquid crystal panel corresponds to the object plane. However, in the above evaluation of the zoom lens systems of the embodiments, they are regarded as reduction systems (for example, taking optical systems) having the object plane on the screen, and their optical performance is evaluated on the surface of the liquid crystal panel.
As described heretofore, according to the present invention, it is possible to realize a zoom lens system that has a sufficiently long back focal length and sufficiently high distortion correction performance for use as a projection optical system. In addition, depending on how the present invention is embodied, it is also possible to reduce under-side distortion caused by the light beams incident on the peripheral portion of the first lens unit, or correct coma aberration satisfactorily.
TABLE 1______________________________________<<Embodiment 1>>f = 72.4.about.59.0.about.48.3FNO = 2.97.about.2.67.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 316.464 d1 = 2.500 N1 = 1.62041 .nu.1 = 60.29r2 = 51.034 d2 = 8.500r3 = -1109.915 d3 = 2.500 N2 = 1.62041 .nu.2 = 60.29r4 = 65.867 d4 = 2.000r5 = 63.217 d5 = 6.500 N3 = 1.70055 .nu.3 = 30.11r6 = 617.791 d6 = 3.000.about.19.734.about.40.232{Second Lens Unit Gr2 . . . Positive}r7 = 54.458 d7 = 5.000 N4 = 1.62280 .nu.4 = 56.88r8 = -1107.003 d8 = 3.000r9 = 74.844 d9 = 3.000 N5 = 1.80518 .nu.5 = 25.43r10 = 33.417 d10 = 2.000r11 = 38.958 d11 = 5.000 N6 = 1.62280 .nu.6 = 56.88r12 = -412.104 d12 = 27.918.about.13.750.about.2.500{Third Lens Unit Gr3 . . . Negative}r13 = 57.598 d13 = 6.000 N7 = 1.75520 .nu.7 = 27.51r14 = 79.864 d14 = 5.000r15 = -1091.012 d15 = 3.000 N8 = 1.65446 .nu.8 = 33.86r16 = 52.634 d16 = 16.000.about.23.000.about.30.000{Fourth Lens Unit Gr4 . . . Positive}r17 = -81.266 d17 = 2.500 N9 = 1.65446 .nu.9 = 33.86r18 = 160.749 d18 = 4.000r19 = -517.221 d19 = 8.000 N10 = 1.62041 .nu.10 = 60.29r20 = -48.410 d20 = 0.100r21 = 129.160 d21 = 7.000 N11 = 1.62041 .nu.11 = 60.29r22 = -276.582 d22 = 0.100r23 = 53.499 d23 = 7.000 N12 = 1.62041 .nu.12 = 60.29r24 = 128.208 d24 = 5.000{Dichroic Prism PR}r25 = .infin. d25 = 40.000 N13 = 1.51680 .nu.13 = 64.20r26 = .infin.______________________________________
TABLE 2______________________________________<<Embodiment 2>>f = 72.5.about.59.0.about.48.3FNO = 2.97.about.2.67.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 189.613 d1 = 2.500 N1 = 1.62041 .nu.1 = 60.29r2 = 51.922 d2 = 8.500r3 = 186.604 d3 = 2.500 N2 = 1.62041 .nu.2 = 60.29r4 = 44.973 d4 = 2.000r5 = 43.578 d5 = 6.500 N3 = 1.70055 .nu.3 = 30.11r6 = 100.517 d6 = 3.000.about.19.075.about.38.744{Second Lens Unit Gr2 . . . Positive}r7 = 32.614 d7 = 2.100 N4 = 1.54072 .nu.4 = 47.22r8 = 29.614 d8 = 4.000r9 = 54.769 d9 = 8.000 N5 = 1.67000 .nu.5 = 57.07r10 = -39.193 d10 = 2.000 N6 = 1.80518 .nu.6 = 25.43r11 = -87.819 d11 = 28.414.about.13.967.about.2.500{Third Lens Unit Gr3 . . . Negative}r12 = 46.438 d12 = 6.000 N7 = 1.75520 .nu.7 = 27.51r13 = 65.485 d13 = 5.000r14 = -1037.119 d14 = 3.000 N8 = 1.65446 .nu.8 = 33.86r15 = 46.889 d15 = 16.000.about.23.000.about.30.000{Fourth Lens Unit Gr4 . . . Positive}r16 = -99.666 d16 = 2.500 N9 = 1.65446 .nu.9 = 33.86r17 = 141.044 d17 = 4.000r18= -1537.137 d18 = 8.000 N10 = 1.62041 .nu.10 = 60.29r19 = -54.444 d19 = 0.100r20 = 124.089 d20 = 7.000 N11 = 1.62041 .nu.11 = 60.29r21 = -303.463 d21 = 0.100r22 = 60.690 d22 = 7.000 N12 = 1.62041 .nu.12 = 60.29r23 = 184.018 d23 = 5.000{Dichroic Prism PR}r24 = .infin. d24= 40.000 N13 = 1.51680 .nu.13 = 64.20r25 = .infin.______________________________________
TABLE 3______________________________________<<Embodiment 3>>f = 72.5.about.59.0.about.48.3FNO = 2.97.about.2.67.about.2.50______________________________________Radius of Axial Retractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 299.533 d1 = 3.000 N1 = 1.67000 .nu.1 = 57.07r2 = 43.743 d2 = 10.000r3 = -324.130 d3 = 2.500 N2 = 1.67000 .nu.2 = 57.07r4 = 83.499 d4 = 0.100r5 = 60.426 d5 = 7.000 N3 = 1.65016 .nu.3 = 39.34r6 = -359.476 d6 = 3.000.about.17.269.about.34.315{Second Lens Unit Gr2 . . . Positive}r7 = 78.555 d7 = 6.000 N4 = 1.61800 .nu.4 = 63.39r8 = -160.001 d8 = 1.000r9 = 59.400 d9 = 3.000 N5 = 1.84666 .nu.5 = 23.82r10 = 35.032 d10 = 2.000r11 = 38.680 d11 = 5.000 N6 = 1.63854 .nu.6 = 55.62r12 = 253.937 d12 = 22.882.about.11.556.about.2.500{Third Lens Unit Gr3 . . . Negative}r13 = 46.059 d13 = 6.000 N7 = 1.75520 .nu.7 = 27.51r14 = -161.049 d14 = 2.000 N8 = 1.61293 .nu.8 = 36.96r15 = 40.296 d15 = 8.000r16 = -100.223 d16 = 3.000 N9 = 1.68893 .nu.9 = 31.16r17 = 51.666 d17 = 9.000.about.16.000.about.21.000{Fourth Lens Unit Gr4 . . . Positive}r18 = -162.014 d18 = 3.000 N10 = 1.80518 .nu.10 = 25.43r19 = 164.804 d19 = 12.000 N11 = 1.62041 .nu.11 = 60.29r20 = -51.160 d20 = 0.100r21 = 133.999 d21 = 7.000 N12 = 1.62041 .nu.12 = 60.29r22 = -203.262 d22 = 0.100r23 = 70.899 d23 = 6.000 N13 = 1.62041 .nu.13 = 60.29r24 = 178.783 d24 = 5.000{Dichroic Prism PR}r25 = .infin. d25 = 40.000 N14 = 1.51680 .nu.14 = 64.20r26 = .infin.______________________________________
TABLE 4______________________________________<<Embodiment 4>>f = 72.4.about.59.0.about.48.3FNO = 2.97.about.2.67.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 139.986 d1 = 3.000 N1 = 1.67000 .nu.1 = 57.07r2 = 42.455 d2 = 10.000r3 = -523.335 d3 = 2.500 N2 = 1.67000 .nu.2 = 57.07r4 = 79.258 d4 = 0.100r5 = 57.536 d5 = 8.000 N3 = 1.65446 .nu.3 = 33.86r6 = 743.937 d6 = 3.000.about.15.828.about.31.192{Second Lens Unit Gr2 . . . Positive}r7 = 143.997 d7 = 6.000 N4 = 1.62041 .nu.4 = 60.29r8 = -98.339 d8 = 0.100r9 = 78.103 d9 = 6.000 N5 = 1.67000 .nu.5 = 57.07r10 = -86.259 d10 = 2.000 N6 = 1.80518 .nu.6 = 25.43r11 = 475.767 d11 = 24.092.about.12.158.about.2.500{Third Lens Unit Gr3 . . . Negative}r12 = 39.050 d12 = 7.000 N7 = 1.71736 .nu.7 = 29.42r13 = -93.977 d13 = 2.000 N8 = 1.61293 .nu.8 = 36.96r14 = 36.200 d14 = 7.00094.050 d15 = 3.000 N9 = 1.70055 .nu.9 = 30.11r16 = 48.540 d16 = 9.000.about.16.000.about.21.000{Fourth Lens Unit Gr4 . . . Positive}r17 = -251.136 d17 = 3.000 N10 = 1.80518 .nu.10 = 25.43r18 = 177.780 d18 = 11.000 N11 = 1.62041 .nu.11 = 60.2952.396 d19 = 0.100r20 = 124.493 d20 = 7.000 N12 = 1.62041 .nu.12 = 60.29r21 = -312.736 d21 = 0.100r22 = 66.549 d22 = 6.000 N13 = 1.62041 .nu.13 = 60.29r23 = 187.422 d23 = 5.000{Dichroic Prism PR}r24 = .infin. d24 = 40.000 N14 = 1.51680 .nu.14 = 64.20r25 = .infin.______________________________________
TABLE 5______________________________________<<Embodiment 5>>f = 72.5.about.59.0.about.48.3FNO = 3.00.about.2.70.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 353.937 d1 = 3.000 N1 = 1.67000 .nu.1 = 57.07r2 = 39.026 d2 = 9.000r3 = 44.819 d3 = 6.000 N2 = 1.74000 .nu.2 = 28.26r4 = 60.142 d4 = 4.000.about.17.555.about.33.685{Second Lens Unit Gr2 . . . Positive}r5 = 141.427 d5 = 6.000 N3 = 1.62041 .nu.3 = 60.29r6 = -243.152 d6 = 1.000r7 = 92.373 d7 = 6.000 N4 = 1.62041 .nu.4 = 60.29r8 = -49.728 d8 = 2.000 N5 = 1.84666 .nu.5 = 23.82r9 = -100.052 d9 = 22.187.about.11.196.about.2.500{Third Lens Unit Gr3 . . . Negative}r10 = 50.851 d10 = 5.000 N6 = 1.77551 .nu.6 = 37.90r11 = -495.255 d11 = 2.000r12 = -1256.708 d12 = 2.000 N7 = 1.51680 .nu.7 = 64.20r13 = 34.318 d13 = 8.000r14 = -48.476 d14 = 3.000 N8 = 1.58144 .nu.8 = 40.89r15 = 67.229 d15 = 8.000.about.16.000.about.20.000{Fourth Lens Unit Gr4 . . . Positive}r16 = -224.530 d16 = 3.000 N9 = 1.80518 .nu.9 = 25.43r17 = 93.882 d17 = 12.000 N10 = 1.62041 .nu.10 = 60.29r18 = -49.708 d18 = 0.100r19 = 191.651 d19 = 6.000 N11 = 1.62041 .nu.11 = 60.29r20 = -194.438 d20 = 0.100r21 = 73.204 d21 = 6.000 N12 = 1.62041 .nu.12 = 60.29r22 = 329.202 d22 = 5.000{Dichroic Prism PR}r23 = .infin. d23 = 40.000 N13 = 1.51680 .nu.13 = 64.20r24 = .infin.______________________________________
TABLE 6______________________________________<<Embodiment 6>>f = 72.5.about.59.0.about.48.3FNO = 3.00.about.2.70.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 288.002 d1 = 3.000 N1 = 1.67000 .nu.1 = 57.07r2 = 38.467 d2 = 9.000r3 = 43.775 d3 = 6.000 N2 = 1.74000 .nu.2 = 28.26r4 = 57.390 d4 = 4.000.about.17.378.about.33.322{Second Lens Unit Gr2 . . . Positive}r5 = 147.083 d5 = 6.000 N3 = 1.62041 .nu.3 = 60.29r6 = -220.402 d6 = 1.000r7 = 91.196 d7 = 6.000 N4 = 1.62041 .nu.4 = 60.29r8 = -48.341 d8 = 2.000 N5 = 1.84666 .nu.5 = 23.82r9 = -100.812 d9 = 22.286.about.11.254.about.2.500{Third Lens Unit Gr3 . . . Negative}r10 = 51.843 d10 = 5.000 N6 = 1.77551 .nu.6 = 37.90r11 = -747.669 d11 = 2.000r12 = 2562.985 d12 = 2.000 N7 = 1.51680 .nu.7 = 64.20r13 = 35.108 d13 = 8.000r14 = -53.142 d14 = 3.000 N8 = 1.58144 .nu.8 = 40.89r15 = 60.025 d15 = 8.000.about.16.000.about.20.000{Fourth Lens Unit Gr4 . . . Positive}r16 = -114.822 d16 = 7.000 N9 = 1.62041 .nu.9 = 60.29r17 = -47.857 d17 = 0.100r18 = 407.030 d18 = 12.000 N10 = 1.62041 .nu.10 = 60.29r19 = -40.074 d19 = 2.000 N11 = 1.75520 .nu.11 = 27.51r20 = -105.152 d20 = 0.100r21 = 82.741 d21 = 8.000 N12 = 1.62041 .nu.12 = 60.29r22 = -596.403 d22 = 5.000{Dichroic Prism PR}r23 = .infin. d23 = 40.000 N13 = 1.51680 .nu.13 = 64.20r24 = .infin.______________________________________
TABLE 7______________________________________<<Embodiment 7>>f = 72.4.about.59.0.about.48.3FNO = 2.97.about.2.67.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 99.982 d1 = 3.000 N1 = 1.67000 .nu.1 = 57.07r2 = 39.202 d2 = 10.000r3 = 641.149 d3 = 2.500 N2 = 1.67090 .nu.2 = 57.07r4 = 62.726 d4 = 0.100r5 = 47.393 d5 = 8.000 N3 = 1.68150 .nu.3 = 36.64r6 = 228.628 d6 = 4.000.about.17.191.about.32.988{Second Lens Unit Gr2 . . . Positive}r7 = 90.814 d7 = 6.000 N4 = 1.61800 .nu.4 = 63.39r8 = -45.723 d8 = 1.000r9 = -41.104 d9 = 2.000 N5 = 1.84666 .nu.5 = 23.82r10 = -66.311 d10 = 35.491.about.17.330.about.2.500{Third Lens Unit Gr3 . . . Negative}r11 = 50.037 d11 = 9.000 N6 = 1.71736 .nu.6 = 29.42r12 = -80.090 d12 = 2.000 N7 = 1.58144 .nu.7 = 40.89r13 = 54.822 d13 = 8.000r14 = -90.855 d14 = 3.000 N8 = 1.71736 .nu.8 = 29.42r15 = 59.803 d15 = 9.000.about.17.000.about.23.000{Fourth Lens Unit Gr4 . . . Positive}r16 = -251.215 d16 = 3.000 N9 = 1.80518 .nu.9 = 25.43r17 = 126.603 d17 = 14.000 N10 = 1.62041 .nu.10 = 60.29r18 = -53.298 d18 = 0.100r19 = 105.096 d19 = 8.000 N11 = 1.62041 .nu.11 = 60.29r20 = -357.060 d20 = 0.100r21 = 62.865 d21 = 8.000 N12 = 1.62041 .nu.12 = 60.29r22 = 131.911 d22 = 5.000{Dichroic Prism PR}r23 = .infin. d23 = 40.000 N13 = 1.51680 .nu.13 = 64.20r24 = .infin.______________________________________
TABLE 8______________________________________<<Embodiment 8>>f = 72.5.about.59.0.about.48.3FNO = 2.97.about.2.67.about.2.50______________________________________Radius of Axial Refractive AbbeCur.nu.ature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 61.778 d1 = 3.000 N1 = 1.62041 .nu.1 = 60.29r2 = 30.825 d2 = 12.000r3 = 216.839 d3 = 2.500 N2 = 1.62041 .nu.2 = 60.29r4 = 56.974 d4 = 0.100r5 = 37.959 d5 = 8.000 N3 = 1.80518 .nu.3 = 25.43r6 = 57. 233 d6 = 3.000.about.14.021.about.27.381{Second Lens Unit Gr2 . . . Positive}r7 = 57.243 d7 = 2.000 N4 = 1.54072 .nu.4 = 47.22r8 = 37.025 d8 = 2.000r9 = 48.640 d9 = 8.000 N5 = 1.67000 .nu.5 = 57.07r10 = -33.005 d10 = 2.000 N6 = 1.80518 .nu.6 = 25.43r11 = -68.624 d11 = 27.020.about.13.556.about.2.500{Third Lens Unit Gr3 . . . Negative}r12 = 48.268 d12 = 8.000 N7 = 1.77551 .nu.7 = 37.90r13 = -97.939 d13 = 2.000 N8 = 1.51680 .nu.8 = 64.20r14 = 36.343 d14 = 8.000r15 = -79.997 d15 = 3.000 N9 = 1.75520 .nu.9 = 27.51r16 = 56.233 d16 = 9.000.about.18.000.about.23.000{Fourth Lens Unit Gr4 . . . Positive}r17 = -697.141 d17 = 3.000 N10 = 1.80518 .nu.10 = 25.43r18 = 266.732 d18 = 12.000 N11 = 1.62041 .nu.11 = 60.29r19 = -59.3.77 d19 = 0.100r20 = 259.666 d20 = 7.000 N12 = 1.62041 .nu.12 = 6.029r21 = -218.211 d21 = 0.100r22 = 68.286 d22 = 9.000 N13 = 1.62041 .nu.13 = 60.29r23 = 474.590 d23 = 5.000{Dichroic Prism PR}r24 = .infin. d24 = 40.000 N14 = 1.51680 .nu.14 = 64.20r25 = .infin.______________________________________
TABLE 9______________________________________<<Embodiment 9>>f = 72.4.about.59.0.about.48.3FNO = 3.14.about.2.78.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 76.274 d1 = 3.000 N1 = 1.67000 .nu.1 = 57.07r2 = 33.536 d2 = 12.000r3 = 371.793 d3 = 2.500 N2 = 1.62041 .nu.2 = 60.29r4 = 73.146 d4 = 0.100r5 = 42.192 d5 = 8.000 N3 = 1.80518 .nu.3 = 25.43r6 = 65.750 d6 = 3.000.about.14.015.about.27.361{Second Lens Unit Gr2 . . . Positive}r7 = 58.137 d7 = 2.000 N4 = 1.63980 .nu.4 = 34.55r8 = 35.437 d8 = 2.000r9 = 44.006 d9 = 10.000 N5 = 1.67000 .nu.5 = 57.07r10 = -37.614 d10 = 2.000 N6 = 1.80518 .nu.6 = 25.43r11 = -71.104 d11 = 28.502.about.14.195.about.2.500{Third Lens Unit Gr3 . . . Negative}r12 = 60.641 d12 = 8.000 N7 = 1.80518 .nu.7 = 25.43r13 = -60.526 d13 = 2.000 N8 = 1.65446 .nu.8 = 33.86r14 = 57.826 d14 = 8.000r15 = -79.015 d15 = 3.000 N9 = 1.75520 .nu.9 = 27.51r16 = 68.547 d16 = 10.000.about.18.000.about.22.000{Fourth Lens Unit Gr4 . . . Positive}r17 = -109.689 d17 = 3.000 N10 = 1.80518 .nu.10 = 25.43r18 = 288.713 d18 = 1.500r19 = 706.125 d19 = 13.500 N11 = 1.62041 .nu.11 = 60.29r20 = -47.094 d20 = 0.100r21 = 144.481 d21 = 8.500 N12 = 1.62041 .nu.12 = 60.29r22 = -238.467 d22 = 0.100r23 = 67.736 d23 = 9.000 N13 = 1.62041 .nu.13 = 60.29r24 = 243.622 d24 = 5.000{Dichroic Prism PR}r25 = .infin. d25 = 40.000 N14 = 1.51680 .nu.14 = 64.20r26 = .infin.______________________________________
TABLE 10______________________________________<<Embodiment 10>>f = 72.4.about.59.0.about.48.3FNO = 3.08.about.2.76.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 67.229 d1 = 3.800 N1 = 1.67000 .nu.1 = 57.07r2 = 32.831 d2 = 11.300r3 = 136.958 d3 = 3.200 N2 = 1.62041 .nu.2 = 60.29r4 = 55.928 d4 = 0.100r5 = 37.783 d5 = 6.000 N3 = 1.70055 .nu.3 = 30.11r6 = 54.629 d6 = 3.000.about.14.138.about.27.401{Second Lens Unit Gr2 . . . Positive}r7 = 50.009 d7 = 2.100 N4 = 1.54072 .nu.4 = 47.20r8 = 38.289 d8 = 4.000r9 = 52.228 d9 = 8.000 N5 = 1.67000 .nu.5 = 57.07r10 = -44.828 d10 = 2.000 N6 = 1.80518 .nu.6 = 25.43r11 = -84.690 d11 = 29.014.about.13.668.about.1.500{Third Lens Unit Gr3 . . . Negative}r12 = 70.349 d12 = 8.500 N7 = 1.80518 .nu.7 = 25.43r13 = -70.474 d13 = 1.000r14 = -59.794 d14 = 2.400 N8 = 1.63980 .nu.8 = 34.55r15 = 65.314 d15 = 6.500r16 = -82.655 d16 = 2.400 N9 = 1.80518 .nu.9 = 25.43r17 = 108.628 d17 = 8.000.about.17.000.about.20.000{Fourth Lens Unit Gr4 . . . Positive}r18 = -86.860 d18 = 3.200 N10 = 1.80518 .nu.10 = 25.43r19 = 193.127 d19 = 2.000r20 = 1109.632 d20 = 11.500 N11 = 1.62041 .nu.11 = 60.29r21 = -46.724 d21 = 0.100r22 = 126.117 d22 = 8.500 N12 = 1.62041 .nu.12 = 60.29r23 = -176.025 d23 = 0.100r24 = 75.118 d24 = 8.500 N13 = 1.62041 .nu.13 = 60.29r25 = 571.811 d25 = 5.000{Dichroic Prism PR}r26 = .infin. d26 = 41.200 N14 = 1.51680 .nu.14 = 64.20r27 = .infin.______________________________________
TABLE 11______________________________________<<Embodiment 11>>f = 72.4.about.59.0.about.48.3FNO = 2.97.about.2.67.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 490.314 d1 = 3.000 N1 = 1.62041 .nu.1 = 60.29r2 = 52.502 d2 = 8.000r3 = 123.723 d3 = 2.500 N2 = 1.62041 .nu.2 = 60.29r4 = 46.378 d4 = 4.000r5 = 69.600 d5 = 8.000 N3 = 1.58340 .nu.3 = 30.23r6* = -8645.285 d6 = 3.000.about.20.745.about.42.387{Second Lens Unit Gr2 . . . Positive}r7 = 55.285 d7 = 5.000 N4 = 1.62041 .nu.4 = 60.29r8 = 630.716 d8 = 3.000r9 = 77.736 d9 = 3.000 N5 = 1.80518 .nu.5 = 25.43r10 = 35.712 d10 = 2.000r11 = 40.820 d11 = 5.000 N6 = 1.62041 .nu.6 = 60.29r12 = -200.843 d12 = 24.411.about.12.180.about.2.500{Third Lens Unit Gr3 . . . Negative}r13 = 56.681 d13 = 6.000 N7 = 1.80518 .nu.7 = 25.43r14 = 90.760 d14 = 5.000r15 = -767.483 d15 = 3.000 N8 = 1.78560 .nu.8 = 42.81r16 = 49.998 d16 = 20.000.about.26.000.about.32.000{Fourth Lens Unit Gr4 . . . Positive}r17 = -209.960 d17 = 2.500 N9 = 1.80518 .nu.9 = 25.43r18 = 130.313 d18 = 4.000r19 = -5033.979 d19 = 8.000 N10 = 1.62041 .nu.10 = 60.29r20 = -55.834 d20 = 0.100r21 = 116.193 d21 = 7.000 N11 = 1.62041 .nu.11 = 60.29r22 = -522.272 d22 = 0.100r23 = 54.492 d23 = 7.000 N12 = 1.62041 .nu.12 = 60.29r24 = 120.748 d24 = 5.000{Dichroic Prism PR}r25 = .infin. d25 = 40.000 N13 = 1.51680 .nu.13 = 64.20r26 = .infin.�Aspherical Coefficients!r6: .epsilon. = 1.0000A4 = -0.11771 .times. 10.sup.-5A6 = -0.15279 .times. 10.sup.-10A8 = -0.57687 .times. 10.sup.-12______________________________________
TABLE 12______________________________________<<Embodiment 12>>f = 72.5.about.59.0.about.48.3FNO = 2.97.about.2.67.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 497.208 d1 = 3.000 N1 = 1.62041 .nu.1 = 60.29r2 = 52.330 d2 = 8.000r3 = 100.495 d3 = 2.500 N2 = 1.62041 .nu.2 = 60.29r4 = 45.614 d4 = 4.000r5 = 67.940 d5 = 8.000 N3 = 1.58340 .nu.3 = 30.23r6* = 648.311 d6 = 3.000.about.20.559.about.41.978{Second Lens Unit Gr2 . . . Positive}r7 = 56.862 d7 = 5.000 N4 = 1.62041 .nu.4 = 60.29r8 = 471.054 d8 = 3.000r9 = 75.752 d9 = 3.000 N5 = 1.80518 .nu.5 = 25.43r10 = 36.084 d10 = 2.000r11 = 41.292 d11 = 5.000 N6 = 1.62041 .nu.6 = 60.29r12 = -180.515 d12 = 24.817.about.12.364.about.2.500{Third Lens Unit Gr3 . . . Negative}r13 = 56.375 d13 = 6.000 N7 = 1.80518 .nu.7 = 25.43r14 = 89.956 d14 = 5.000r15 = -875.090 d15 = 3.000 N8 = 1.78560 .nu.8 = 42.81r16 = 50.545 d16 = 20.000.about.26.000.about.32.000{Fourth Lens Unit Gr4 . . . Positive}r17 = -211.092 d17 = 2.500 N9 = 1.80518 .nu.9 = 25.43r18 = 130.130 d18 = 4.000r19 = -2977.875 d19 = 8.000 N10 = 1.62041 .nu.10 = 60.29r20 = -55.499 d20 = 0.100r21 = 116.254 d21 = 7.000 N11 = 1.62041 .nu.11 = 60.29r22 = -521.010 d22 = 0.100r23 = 54.182 d23 = 7.000 N12 = 1.62041 .nu.12 = 60.29r24 = 119.123 d24 = 5.000{Dichroic Prism PR}r25 = .infin. d25 = 40.000 N13 = 1.51680 .nu.13 = 64.20r26 = .infin.�Aspherical Coefficients!r6: .epsilon. = 1.0000A4 = -0.11631 .times. 10.sup.-5A6 = -0.24968 .times. 10.sup.-10A8 = -0.55642 .times. 10.sup.-12______________________________________
TABLE 13______________________________________<<Embodiment 13>>f = 82.5.about.65.0.about.55.0FNO = 2.97.about.2.67.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 862.232 d1 = 4.000 N1 = 1.62041 .nu.1 = 60.29r2 = 44.140 d2 = 10.000r3 = -162.503 d3 = 3.000 N2 = 1.62041 .nu.2 = 60.29r4 = 195.625 d4 = 0.500r5 = 88.362 d5 = 5.000 N3 = 1.84666 .nu.3 = 23.82r6 = 418.176 d6 = 3.000.about.15.766.about.26.707{Second Lens Unit Gr2 . . . Positive}r7 = 107.383 d7 = 5.000 N4 = 1.61800 .nu.4 = 63.39r8 = -111.942 d8 = 0.500r9 = 70.519 d9 = 3.000 N5 = 1.84666 .nu.5 = 23.82r10 = 37.867 d10 = 7.000 N6 = 1.61800 .nu.6 = 63.39r11 = -420.978 d11 = 23.041.about.9.969.about.2.500{Third Lens Unit Gr3 . . . Positive}(Front Lens Sub-unit . . . Negative)r12 = 35.819 d12 = 6.000 N7 = 1.80518 .nu.7 = 25.43r13 = 59.423 d13 = 3.000r14 = 188.974 d14 = 3.000 N8 = 1.74000 .nu.8 = 31.72r15 = 36.572 d15 = 8.000r16 = 536.386 d16 = 4.000 N9 = 1.84666 .nu.9 = 23.82r17 = 53.063 d17 = 20.500(Rear Lens Sub-unit . . . Positive)r18 = -1063.366 d18 = 6.000 N10 = 1.62041 .nu.10 = 60.29r19 = -78.508 d19 = 0.100r20 = -724.743 d20 = 7.500 N11 = 1.62041 .nu.11 = 60.29r21 = -97.491 d21 = 0.100r22 = 61.183 d22 = 8.000 N12 = 1.51680 .nu.12 = 64.20r23 = 263.940 d23 = 5.000{Dichroic Prism PR}r24 = .infin. d24 = 40.000 N13 = 1.51680 .nu.13 = 64.20r25 = .infin.______________________________________
TABLE 14______________________________________<<Embodiment 14>>f = 82.5.about.65.0.about.55.0FNO = 2.95.about.2.66.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 1276.194 d1 = 4.000 N1 = 1.51680 .nu.1 = 64.20r2 = 48.518 d2 = 9.000r3 = -1827.252 d3 = 4.000 N2 = 1.51680 .nu.2 = 64.20r4 = 252.429 d4 = 1.000r5 = 59.903 d5 = 6.500 N3 = 1.80518 .nu.3 = 25.43r6 = 83.140 d6 = 2.000.about.20.893.about.37.086{Second Lens Unit Gr2 . . . Positive}r7 = 142.301 d7 = 6.000 N4 = 1.69680 .nu.4 = 56.47r8 = -125.949 d8 = 0.500r9 = 143.769 d9 = 9.000 N5 = 1.69680 .nu.5 = 56.47r10 = -47.833 d10 = 3.000 N6 = 1.75520 .nu.6 = 27.51643.803 d11 = 23.612.about.10.177.about.2.500{Third Lens Unit Gr3 . . . Positive}(Front Lens Sub-unit . . . Negative)r12 = 33.100 d12 = 8.000 N7 = 1.84666 .nu.7 = 23.82r13 = 33.554 d13 = 8.000r14 = -146.016 d14 = 4.000 N8 = 1.68150 .nu.8 = 36.64r15 = 43.148 d15 = 15.000(Rear Lens Sub-unit . . . Positive)r16 = 493.140 d16 = 4.000 N9 = 1.80518 .nu.9 = 25.43r17 = 85.960 d17 = 15.000 N10 = 1.69680 .nu.10 = 56.47r18 = -71.017 d18 = 0.500r19 = 93.480 d19 = 12.000 N11 = 1.69680 .nu.11 = 56.47r20 = -271.857 d20 = 5.000{Dichroic Prism PR}r21 = .infin. d21 = 40.000 N12 = 1.51680 .nu.12 = 64.20r22 = .infin.______________________________________
TABLE 15______________________________________<<Embodiment 15>>f = 82.5.about.65.0.about.55.0FNO = 3.02.about.2.69.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 676.585 d1 = 4.000 N1 = 1.61800 .nu.1 = 63.39r2 = 45.769 d2 = 11.163r3 = 44.004 d3 = 4.000 N2 = 1.84666 .nu.2 = 23.82r4 = 50.240 d4 = 2.000.about.17.471.about.30.732{Second Lens Unit Gr2 . . . Positive}r5 = 62.527 d5 = 5.000 N3 = 1.61800 .nu.3 = 63.39r6 = 754.256 d6 = 0.500r7 = 82.261 d7 = 3.000 N4 = 1.80518 .nu.4 = 25.43r8 = 41.588 d8 = 2.000r9 = 54.541 d9 = 7.000 N5 = 1.61800 .nu.5 = 63.39r10 = -137.617 d10 = 27.781.about.11.375.about.2.000{Third Lens Unit Gr3 . . . Positive}(Front Lens Sub-unit . . . Negative)r11 = 33.190 d11 = 8.000 N6 = 1.84666 .nu.6 = 23.82r12 = 32.840 d12 = 14.000r13 = -103.203 d13 = 4.000 N7 = 1.68150 .nu.7 = 36.64r14 = 45.848 d14 = 10.000(Rear Lens Sub-unit . . . Positive)r15 = 5254.861 d15 = 4.000 N8 = 1.80518 .nu.8 = 25.43r16 = 93.889 d16 = 12.000 N9 = 1.69680 .nu.9 = 56.47r17 = -63.501 d17 = 0.500r18 = 68.713 d18 = 16.000 N10 = 1.61800 .nu.10 = 63.39r19 = -170.704 d19 = 5.000{Dichroic Prism PR}r20 = .infin. d20 = 40.000 N11 = 1.51680 .nu.11 = 64.20r21 = .infin.______________________________________
TABLE 16______________________________________<<Embodiment 16>>f = 82.5.about.65.0.about.55.0FNO = 3.02.about.2.69.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 154.353 d1 = 4.000 N1 = 1.61800 .nu.1 = 63.39r2 = 40.773 d2 = 10.392r3 = 42.203 d3 = 7.000 N2 = 1.70055 .nu.2 = 30.11r4 = 58.991 d4 = 7.517r5 = 839.835 d5 = 3.000 N3 = 1.61800 .nu.3 = 63.39r6 = 141.920 d6 = 3.000.about.18.869.about.32.472{Second Lens Unit Gr2 . . . Positive}r7 = 68.935 d7 = 5.000 N4 = 1.61800 .nu.4 = 63.39r8 = -1402.564 d8 = 0.500r9 = 82.107 d9 = 3.000 N5 = 1.80518 .nu.5 = 25.43r10 = 40.768 dl0 = 2.000r11 = 50.572 d11 = 7.000 N6 = 1.61800 .nu.6 = 63.39r12 = -172.006 d12 = 27.634.about.11.640.about.2.500{Third Lens Unit Gr3 . . . Positive}(Front Lens Sub-unit . . . Negative)r13 = 31.907 d13 = 8.000 N7 = 1.84666 .nu.7 = 23.82r14 = 30.613 d14 = 14.000r15 = -94.551 d15 = 4.000 N8 = 1.68150 .nu.8 = 36.64r16 = 47.744 d16 = 10.000(Rear Lens Sub-unit . . . Positive)r17 = 1274.275 d17 = 4.000 N9 = 1.80518 .nu.9 = 25.43r18 = 107.683 d18 = 12.000 N10 = 1.69680 .nu.10 = 56.47r19 = -75.076 d19 = 0.500r20 = 82.235 d20 = 12.000 N11 = 1.61800 .nu.11 = 63.39r21 = -175.539 d21 = 1.000r22 = 624.333 d22 = 7.000 N12 = 1.61800 .nu.12 = 63.39r23 = -285.428 d23 = 5.000{Dichroic Prism PR}r24 = .infin. d24 = 40.000 N13 = 1.51680 .nu.13 = 64.20r25 = .infin.______________________________________
TABLE 17______________________________________<<Embodiment 17>>f = 82.5.about.65.0.about.55.0FNO = 3.02.about.2.69.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 163.467 d1 = 4.000 N1 = 1.61800 .nu.1 = 63.39r2 = 41.485 d2 = 12.992r3 = 47.235 d3 = 7.000 N2 = 1.75520 .nu.2 = 27.51r4 = 63.469 d4 = 5.500r5 = 758.369 d5 = 3.000 N3 = 1.61800 .nu.3 = 63.39r6 = 150.096 d6 = 3.000.about.19.614.about.33.855{Second Lens Unit Gr2 . . . Positive}r7 = 70.851 d7 = 5.000 N4 = 1.61800 .nu.4 = 63.39r8 = -298.018 d8 = 0.500r9 = 86.403 d9 = 3.000 N5 = 1.84666 .nu.5 = 23.82r10 = 42.033 d10 = 2.000r11 = 48.512 d11 = 7.000 N6 = 1.61800 .nu.6 = 63.39r12 = -197.716 d12 = 23.600.about.0.173.about.2.500{Third Lens Unit Gr3 . . . Positive}(Front Lens Sub-unit . . .Negative)r13 = 35.555 d13 = 8.000 N7 = 1.80741 .nu.7 = 31.59r14 = 126.223 d14 = 3.000 N8 = 1.80420 .nu.8 = 46.50r15 = 30.845 d15 = 12.000r16 = -77.498 d16 = 4.000 N9 = 1.72100 .nu.9 = 33.40r17 = 59.063 d17 = 10.000(Rear Lens Sub-unit . . . Positive)r18 = 1235.208 d18 = 4.000 N10 = 1.80518 .nu.10 = 25.43r19 = 93.250 d19 = 12.000 N11 = 1.69680 .nu.11 = 56.47r20 = -72.649 d20 = 0.500r24 = 87.408 d21 = 12.000 N12 = 1.61800 .nu.12 = 63.39r22 = -319.520 d22 = 1.000r23 = 134.980 d23 = 7.000 N13 = 1.61800 .nu.13 = 63.39r24 = -2269.684 d24 = 5.000{Dichroic Prism PR}r25 = .infin. d25 = 40.000 N14 = 1.51680 .nu.14 = 64.20r26 = .infin.______________________________________
TABLE 18______________________________________<<Embodiment 18>>f = 82.5.about.65.0.about.55.0FNO = 2.97.about.2.67.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 230.274 d1 = 4.000 N1 = 1.62041 .nu.1 = 60.29r2 = 43.747 d2 = 12.992r3 = 54.128 d3 = 7.000 N2 = 1.84666 .nu.2 = 23.82r4 = 70.294 d4 = 5.500r5 = 878.850 d5 = 3.000 N3 = 1.62041 .nu.3 = 60.29r6 = 199.785 d6 = 3.000.about.20.043.about.34.652{Second Lens Unit Gr2 . . . Positive}r7 = 72.660 d7 = 5.000 N4 = 1.61800 .nu.4 = 63.39r8 = -220.035 d8 = 0.500r9 = 87.713 d9 = 3.000 N5 = 1.84666 .nu.5 = 23.82r10 = 43.317 d10 = 2.000r11 = 48.919 d11 = 7.000 N6 = 1.61800 .nu.6 = 63.39r12 = -277.691 d12 = 23.069.about.9.980.about.2.500{Third Lens Unit Gr3 . . . Positive}(Front Lens Sub-unit . . . Negative)r13 = 37.693 d13 = 6.000 N7 = 1.84666 .nu.7 = 23.82r14 = 107.578 d14 = 2.000r15 = 103.889 d15 = 3.000 N8 = 1.80741 .nu.8 = 31.59r16 = 31.574 d16 = 12.000r17 = -68.013 d17 = 4.000 N9 = 1.84666 .nu.9 = 23.82r18 = 73.566 d18 = 14.000(Rear Lens Sub-unit . . . Positive)r19 = -488.890 d19 = 9.000 N10 = 1.62041 .nu.10 = 60.29r20 = -57.701 d20 = 0.100r21 = 134.275 d21 = 9.000 N11 = 1.62041 .nu.11 = 60.29r22 = -208.852 d22 = 0.100r23 = 70.235 d23 = 9.000 N12 = 1.51680 .nu.12 = 64.20r24 = 525.351 d24 = 5.000{Dichroic Prism PR}r25 = .infin. d25 = 40.000 N13 = 1.51680 .nu.13 = 64.20r26 = .infin.______________________________________
TABLE 19______________________________________<<Embodiment 19>>f = 82.5.about.65.0.about.55.0FNO = 3.01.about.2.69.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 1155.375 d1 = 3.000 N1 = 1.62041 .nu.1 = 60.29r2 = 45.295 d2 = 10.000r3 = -489.891 d3 = 2.700 N2 = 1.62041 .nu.2 = 60.29r4 = 148.763 d4 = 0.100r5 = 77.002 d5 = 5.000 N3 = 1.75520 .nu.3 = 27.51r6 = 509.009 d6 = 1.500.about.18.911.about.33.836{Second Lens Unit Gr2 . . . Positive}r7 = 59.810 d7 = 5.000 N4 = 1.61800 .nu.4 = 63.39r8 = -16136.841 d8 = 0.100r9 = 76.557 d9 = 2.200 N5 = 1.84666 .nu.5 = 23.82r10 = 40.218 d10 = 2.000r11 = 48.575 d11 = 5.800 N6 = 1.61800 .nu.6 = 63.39r12 = -171.636 d12 = 20.664.about.8.469.about.1.500{Third Lens Unit Gr3 . . . Positive}(Front Lens Sub-unit . . . Negative)r13 = 36.489 d13 = 6.000 N7 = 1.75520 .nu.7 = 27.51r14 = 153.417 d14 = 3.000r15 = 243.127 d15 = 2.200 N8 = 1.74000 .nu.8 = 31.72r16 = 30.516 d16 = 11.500r17 = -90.478 d17 = 2.200 N9 = 1.84666 .nu.9 = 23.82r18 = 77.337 d18 = 18. 000(Rear Lens Sub-unit . . . Positive)r19 = -289.606 d19 = 7.300 N10 = 1.62041 .nu.10 = 60.29r20 = -57.779 d20 = 0.100r21 = 243.162 d21 = 5.700 N11 = 1.62041 .nu.11 = 60.29r22 = -183.238 d22 = 0.100r23 = 71.282 d23 = 7.500 N12 = 1.62041 .nu.12 = 60.29r24 = 361.925 d24 = 5.000{Dichroic Prism PR}r25 = .infin. d25 = 40.000 N13 = 1.51680 .nu.13 = 64.20r26 = .infin.______________________________________
TABLE 20______________________________________<<Embodiment 20>>f = 72.5.about.59.0.about.48.3FNO = 2.97.about.2.67.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 1556.687 d1 = 3.000 N1 = 1.69680 .nu.1 = 56.47r2 = 43.952 d2 = 12.000r3 = 245.668 d3 = 9.100 N2 = 1.58340 .nu.2 = 30.23r4* = -263.429 d4 = 3.000.about.19.718.about.39.667{Second Lens Unit Gr2 . . . Positive}r5 = 73.385 d5 = 5.000 N3 = 1.61800 .nu.3 = 63.39r6 = -1167.352 d6 = 3.000r7 = 65.715 d7 = 3.000 N4 = 1.84666 .nu.4 = 23.82r8 = 45.705 d8 = 2.000r9 = 58.016 d9 = 5.000 N5 = 1.61800 .nu.5 = 63.39r10 = -249.272 d10 = 20.255.about.10.367.about.2.500{Third Lens Unit Gr3 . . . Positive}(Front Lens Sub-unit . . . Negative)r11 = 36.070 d11 = 6.000 N6 = 1.71736 .nu.6 = 29.42r12 = 145.958 d12 = 2.000r13 = 602.177 d13 = 3.000 N7 = 1.75450 .nu.7 = 32.83r14 = 30.657 d14 = 14.000r15 = -407.953 d15 = 4.000 N8 = 1.84666 .nu.8 = 23.82r16* = 55.298 d16 = 10.000(Rear Lens Sub-unit . . . Positive)r17 = 210.544 d17 = 7.500 N9 = 1.51680 .nu.9 = 64.20r18 = -72.462 d18 = 0.100r19 = 232.260 d19 = 7.000 N10 = 1.51680 .nu.10 = 64.20r20 = -96.967 d20 = 0.100r21 = 66.285 d21 = 8.500 N11 = 1.51680 .nu.11 = 64.20r22 = 1665.917 d22 = 5.000{Dichroic Prism PR}r23 = .infin. d23 = 40.000 N12 = 1.51680 .nu.12 = 64.20r24 = .infin.�Aspherical Coefficients!r4: .epsilon. = 1.0000A4 = -0.11319 .times. 10.sup.-5A6 = 0.12489 .times. 10.sup.-9A8 = -0.47125 .times. 10.sup.-12r16: .epsilon. = 1.0000A4 = -0.96751 .times. 10.sup.-6A6 = -0.72732 .times. 10.sup.-9A8 = -0.63656 .times. 10.sup.-12______________________________________
TABLE 21______________________________________<<Embodiment 21>>f = 72.5.about.59.0.about.48.3FNO = 2.97.about.2.67.about.2.50______________________________________Radius of Axial Refractive AbbeCurvature Distance Index Number______________________________________{First Lens Unit Gr1 . . . Negative}r1 = 394.515 d1 = 3.000 N1 = 1.62041 .nu.1 = 60.29r2 = 42.736 d2 = 12.000r3 = 1340.770 d3 = 2.500 N2 = 1.62041 .nu.2 = 60.29r4 = 148.339 d4 = 0.100r5 = 88.727 d5 = 6.500 N3 = 1.58340 .nu.3 = 30.23r6* = 2897.123 d6 = 3.000.about.19.168.about.38.462{Second Lens Unit Gr2 . . . Positive}r7 = 79.565 d7 = 5.000 N4 = 1.61800 .nu.4 = 63.39r8 = 987.596 d8 = 3.000r9 = 68.314 d9 = 3.000 N5 = 1.84666 .nu.5 = 23.82r10 = 38.820 d10 = 2.000r11 = 44.052 d11 = 6.000 N6 = 1.61800 .nu.6 = 63.39r12 = -130.793 d12 = 20.859.about.10.634.about.2.500{Third Lens Unit Gr3 . . . Positive}(Front Lens Sub-unit . . . Negative)r13 = 40.530 d13 = 8.000 N7 = 1.80518 .nu.7 = 25.43r14 = 153.636 d14 = 3.000 N8 = 1.65446 .nu.8 = 33.86r15 = 30.126 d15 = 12.000r16 = -120.615 d16 = 4.000 N9 = 1.84666 .nu.9 = 23.82r17 = 63.866 d17 = 14.000(Rear Lens Sub-unit . . . Positive)r18 = -175.064 d18 = 5.600 N10 = 1.62041 .nu.10 = 60.2919 = -56.865 d19 = 0.100r20 = 119.748 d20 = 8.200 N11 = 1.51680 .nu.11 = 64.20r21 = -158.512 d21 = 0.100r22 = 63.645 d22 = 9.000 N12 = 1.51680 .nu.12 = 64.20r23 = 793.405 d23 = 5.000{Dichroic Prism PR}r24 = .infin. d24 = 40.000 N13 = 1.51680 .nu.13 = 64.20r25 = .infin.�Aspherical Coefficients!r6: .epsilon. = 1.0000A4 = -0.57067 .times. 10.sup.-6A6 = -0.13108 .times. 10.sup.-9A8 = 0.26152 .times. 10.sup.-10______________________________________
TABLE 22______________________________________ Cond. (1) Cond. (2) Cond. (3) Cond. (4)______________________________________Type A Emb. 1 0.388 6.174 -- -- Emb. 2 0.381 5.876 -- --Type B Emb. 3 0.725 -- 14.984 -- Emb. 4 0.725 -- 26.404 --Type C Emb. 5 0.749 -- 5.151 0.041 Emb. 6 0.749 -- 5.196 0.04lType B Emb. 7 0.516 -- 21.914 -- Emb. 8 0.676 -- 7.095 -- Emb. 9 0.628 -- 42.084 --Type C Emb. 10 0.565 -- 26.944 0.021Type A Emb. 11 0.463 4.326 -- -- Emb. 12 0.449 4.358 -- --______________________________________
TABLE 23______________________________________ Cond. (5) Cond. (6) Cond. (7) Cond. (8)______________________________________Type A Emb. 1 -- 27.51 -- -- Emb. 2 -- 27.51 -- --Type B Emb. 3 -- -- 13.30 0.919 Emb. 4 -- -- 18.31 0.939Type C Emb. 5 0.0012 -- 13.87 0.854 Emb. 6 0.0017 -- 14.48 0.854Type B Emb. 7 -- -- 19.15 0.921 Emb. 8 -- -- 18.16 0.854 Emb. 9 -- -- 14.54 0.917Type C Emb. 10 -0.0025 -- 12.60 0.908Type A Emb. 11 -- 25.43 -- -- Emb. 12 -- 25.43 -- --______________________________________
TABLE 24______________________________________ Cond. (9) Cond. (10) Cond. (11)______________________________________Type A Emb. 1 -- 0.613 0.810 Emb. 2 -- 0.613 0.796Type B Emb. 3 -- 0.625 0.976 Emb. 4 -- 0.625 1.026Type C Emb. 5 -- 0.606 1.009 Emb. 6 -- 0.606 1.013Type B Emb. 7 -- 0.664 1.014 Emb. 8 -- 0.650 1.044 Emb. 9 -- 0.682 0.967Type C Emb. 10 -- 0.684 0.744Type A Emb. 11 1.58340 0.613 0.783 Emb. 12 1.58340 0.613 0.783______________________________________
TABLE 25______________________________________ Cond. Cond. Cond. Cond. Cond. (12) (2) (3) (4) (5)______________________________________Type D Emb. 13 0.953 4.035 -- -- -- Emb. 14 0.801 146.815 -- -- -- Emb. 15 0.865 188.657 -- -- -- Emb. 16 0.906 48.315 -- -- --Type E Emb. 17 1.016 -- 14.098 -- --Type F Emb. 18 1.137 -- 11.320 0.036 0.0003 Emb. 19 1.099 -- 11.218 0.055 -0.0024 Emb. 20 1.044 -- 12.327 0.041 -0.0052Type E Emb. 21 0.874 -- 6.791 -- --______________________________________
TABLE 26______________________________________ Cond. Cond. Cond. Cond. Cond. (6) (7) (13) (10) (9)______________________________________Type D Emb. 13 25.43 -- 0.502 0.676 -- Emb. 14 23.82 -- 0.563 0.567 -- Emb. 15 -- -- 0.581 0.633 -- Emb. 16 -- -- 0.590 0.633 --Type E Emb. 17 -- 1.83 0.542 0.613 --Type F Emb. 18 -- 1.73 0.551 0.613 -- Emb. 19 -- 24.91 0.531 0.598 -- Emb. 20 -- 24.48 0.472 0.613 1.58340Type E Emb. 21 -- -1.12 0.475 0.613 1.58340______________________________________

Number	Date	Country	Kind
8-288721	Oct 1996	JPX
8-288727	Oct 1996	JPX

Number	Name	Date
4687302	Ikemori et al.	Aug 1987
4824223	Docter et al.	Apr 1989
5009491	Hata	Apr 1991
5132848	Nishio et al.	Jul 1992

Zoom lens system

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CPC

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