Zoom optical system, and electronic equipment incorporating the same Number:7,385,767 from the United States Patent and Trademark Office (PTO) owispatent

Title: Zoom optical system, and electronic equipment incorporating the same

Abstract: The invention concerns a zoom optical system in which, for zooming, an optical function surface is rotated about a point away from it to change the position of a light beam that passes through the optical function surface. The zoom optical system comprises a stop 2 and one or more optical elements 10 located on an object side with respect to the stop 2, each having at least one optical function surface 11, 12, 13, and is adapted to form an image of a distant object O at varying magnifications. At least one optical function surface 12 comprises a continuous surface, and is constructed such that there is a continuous change in at least the radius of curvature in a sectional direction from one end to another end. Upon zooming, at least one optical element 10 having optical function surfaces 11, 12, 13 is rotated about a point S that is not contiguous to one optical function surface.

Patent Number: 7,385,767 Issued on 06/10/2008 to Minakata

---

Inventors:	Minakata; Hiroyuki (Hachioji, JP)
Assignee:	Olympus Corporation (Tokyo, JP)
Appl. No.:	11/072,412
Filed:	March 7, 2005

---

Foreign Application Priority Data

---

Mar 09, 2004 [JP]			2004-065128
Mar 29, 2004 [JP]			2004-094284
Mar 29, 2004 [JP]			2004-094285
Apr 06, 2004 [JP]			2004-112031

Current U.S. Class:	359/678 ; 359/676
Field of Search:	359/676,683,692

---

References Cited [Referenced By]

---

U.S. Patent Documents

6278558	August 2001	Chang
6738199	May 2004	Nishioka
6775073	August 2004	Kamo
2002/0149854	October 2002	Tanaka et al.

Foreign Patent Documents

	2002-139670		May., 2002		JP
	2002-328302		Nov., 2002		JP

Primary Examiner: Sugarman; Scott J
Attorney, Agent or Firm: Kenyon & Kenyon LLP

---

Claims

---

I claim:

1. A zoom optical system, comprising: a stop, and an optical element located on an object side of the zoom optical system with respect to said stop, wherein: said optical element has at least one optical function surface, wherein said at least one optical function surface comprises a continuous surface and is constructed such that a line of intersection of a given reference plane with said optical function surface is configured such that there is a continuous change in at least a radius of curvature from one end toward another end, and said optical element is rotated about a given axis of rotation to implement zooming, wherein: given an axial chief ray defined by a light ray that is incident from a distant object on said optical function surface located nearest to the object side of the zoom optical system, arriving at a center of an image plane through a center of said stop, said given reference plane is defined by a direction vector of said axial chief ray in a direction toward said distant object and a vector that passes through a center of said stop and is vertical to a stop plane, and said given axis of rotation is an axis that passes through a point that is not contiguous to said optical function surface within said given reference plane and is vertical to said given reference plane.

2. A zoom optical system, comprising: a stop, and an optical element located on an object side of the zoom optical system with respect to said stop, wherein said optical element has at least one optical function surface, wherein said at least one optical function surface comprises a continuous surface and is constructed such that a line of intersection of a given reference plane with said optical function surface is configured such that there is a continuous change in at least a radius of curvature from one end toward another end, and said optical element is rotated about a given axis of rotation to implement zooming, wherein: given an axial chief ray defined by a light ray that is incident from a distant object on said optical function surface located nearest to the object side of the zoom optical system, arriving at a center of an image plane through a center of said stop, said given reference plane is defined by a direction vector of said axial chief ray in a direction toward said distant object and a vector that passes through a center of said stop and is vertical to a stop plane, and said given axis of rotation is an axis that passes through a point that is not contiguous to said optical function surface within said given reference plane and is vertical to said given reference plane.

3. A zoom optical system, comprising: a stop, a first optical element located on an object side of the zoom optical system with respect to said stop, and a second optical element located on an image side of the zoom optical system with respect to said stop, wherein: said first optical element comprises at least one optical function surface, and said second optical element comprises at least one optical function surface, wherein: said at least one optical function surface of said first optical element comprises a continuous surface and is constructed such that a line of intersection of a given first reference plane with said optical function surface of said first optical element is configured such that there is a continuous change in at least a radius of curvature from one end toward another end, and said at least one optical function surface of said second optical element comprises a continuous surface and is constructed such that a line of intersection of a given second reference plane with said optical function surface of said second optical element is configured such that there is a continuous change in at least a radius of curvature from one end toward another end, said first optical element is rotated about a given first axis of rotation, and said second optical element is rotated about a given second axis of rotation, wherein: given an axial chief ray defined by a light ray that is incident from a distant object on said optical function surface located nearest to the object side of the zoom optical system, arriving at a center of an image plane through a center of said stop, said given first reference plane for said first optical element is defined by a direction vector of said axial chief ray in a direction toward said distant object and a vector that passes through a center of said stop and is vertical to a stop plane, and said given first axis of rotation is an axis that passes through a point that is not contiguous to said optical function surface within said given first reference plane and is vertical to said given first reference plane, and said given second reference plane for said second optical element is defined by a direction vector of said axial chief ray in a direction toward said distant object and a vector that passes through a center of said stop and is vertical to a stop plane, and said given second axis of rotation is an axis that passes through a point that is not contiguous to said optical function surface within said given second reference plane and is vertical to said given second reference plane.

4. A zoom optical system, comprising: a stop, a first optical element located on an object side of the zoom optical system with respect to said stop, and a second optical element located on an image side of the zoom optical system with respect to said stop, wherein: said first optical element comprises at least one optical function surface, and said second optical element comprises at least one optical function surface, wherein: said at least one optical function surface of said first optical element comprises a continuous surface and is constructed such that a line of intersection of a given first reference plane with said optical function surface of said first optical element is configured such that there is a continuous change in at least a radius of curvature from one end toward another end, and said at least one optical function surface of said second optical element comprises a continuous surface and is constructed such that a line of intersection of a given second reference plane with said optical function surface of said second optical element is configured such that there is a continuous change in at least a radius of curvature from one end toward another end, said first optical element is rotated about a given first axis of rotation while, at the same time, said second optical element is rotated about a given second axis of rotation in the same direction as that of rotation of said first optical element, wherein: given an axial chief ray defined by a light ray that is incident from a distant object on said optical function surface located nearest to the object side of the zoom optical system, arriving at a center of an image plane through a center of said stop, said given first reference plane for said first optical element is defined by a direction vector of said axial chief ray in a direction toward said distant object and a vector that passes through a center of said stop and is vertical to a stop plane, and said given first axis of rotation is an axis that passes through a point that is not contiguous to said optical function surface within said given first reference plane and is vertical to said given first reference plane, and said given second reference plane for said second optical element is defined by a direction vector of said axial chief ray in a direction toward said distant object and a vector that passes through a center of said stop and is vertical to a stop plane, and said given second axis of rotation is an axis that passes through a point that is not contiguous to said optical function surface within said given second reference plane and is vertical to said given second reference plane.

5. The zoom optical system according to claim 1, wherein said optical function surface configured such that there is a continuous change in a radius of curvature in a direction vertical to said given reference plane.

6. The zoom optical system according to claim 1, which further comprises another optical element on the image side of the zoom optical system with respect to said stop, wherein: said another optical element comprises at least one optical function surface, and said at least one optical function surface of said another optical element comprises a continuous surface and is constructed such that a line of intersection of said given reference plane with said optical function surface of said another optical element is configured such that there is a continuous change in a radius of curvature from one end toward another end.

7. The zoom optical system according to claim 6, wherein: the optical function surface of said another optical element is configured such that there is a continuous change in a radius of curvature in a direction orthogonal to said given reference plane.

8. The zoom optical system according to claim 6, wherein: said another optical element is rotated about given another axis of rotation in cooperation with said optical element, wherein: said another given axis of rotation is an axis that passes through a point that is not contiguous to the optical function surface of said another optical element within said reference plane and is vertical to said given another reference plane.

9. The zoom optical system according to claim 1, wherein: an optical function surface positioned right before said stop and an optical function surface positioned right after said stop are rotated in mutually different directions with respect to said stop.

10. The zoom optical system according to claim 1, wherein: said optical element has three or more surfaces.

11. The zoom optical system according to claim 1, wherein: said optical element has at least one rotationally asymmetric surface.

12. The zoom optical system according to claim 1, wherein: an angle of rotation of said optical element upon zoom satisfies condition (1) 0.degree.<.theta.<120.degree. (1) where .theta.is an angle of rotation of the optical element.

13. The zoom optical system according to claim 1, which has a zoom ratio that satisfies condition (2): 1.01<.beta.<20 (2) where .beta.is the zoom ratio.

14. The zoom optical system according to claim 1, which satisfies condition (3): 0<.upsilon..sub.max-.upsilon..sub.min<100 (3) where .upsilon..sub.max is a maximum Abbe constant of an optical element included in said zoom optical system, and .upsilon..sub.min is a minimum Abbe constant of an optical element included in said zoom optical system.

15. The zoom optical system according to claim 1, which has only one image-formation plane.

16. Electronic equipment, comprising: the zoom optical system recited in claim 1, and an image pickup device located on an image side thereof.

17. The electronic equipment according to claim 16, which further comprises means for electrical correction of an image shape formed through said zoom optical system.

18. The Electronic equipment according to claim 17, wherein a parameter that differs for each focal length is used for said correction.

19. The electronic equipment according to claim 17, wherein a parameter that differs for each wavelength area is sued for said correction.

20. The zoom optical system according to claim 1, wherein at least one of the optical function surfaces of said optical element is a reflecting surface.

21. The zoom optical system according to claim 6, wherein at least one of the optical function surfaces of said another optical element is a reflecting surface.

22. The zoom optical system according to claim 6, wherein at least one of the optical function surfaces of said another optical element is a rotationally asymmetric surface.

---

Description

---

This application claims benefit of Japanese Application No. 2004-65128 filed in Japan on Mar. 3, 2004 as well as Japanese Application Nos. 2004-94284 and 2004-94285 filed in Japan on Apr. 6, 2004, the contents of which are incorporated by this reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to a zoom optical system and electronic equipment incorporating the same, and more particularly to a compact zoom optical system and electronic equipment incorporating the same. The electronic equipment contemplated herein, for instance, includes digital cameras, video cameras, digital video units, personal computers, mobile computers, cellular phones and personal digital assistants.

Some optical systems have been proposed for zoom image pickup optical systems made up of free-form surface prisms.

One of those optical systems is designed to move a plurality of prisms for zooming. This arrangement has to previously have a prism movement space therein.

Another optical system is designed to move an aperture with respect to a prism to vary the position of incidence of light rays for zooming. However, this optical system, because of being adapted to from a primary image, becomes bulky. In addition, not only a movement mechanism but also a mechanism for varying an aperture diameter is needed to allow the aperture to have a brightness control function.

Yet another optical system, too, becomes bulky because of being adapted to form a primary image. For zooming, an image-side prism is rotated with the center of rotation on the position of the primary image, resulting in an increase in the amount of movement in association with the rotation of the image-side prism.

SUMMARY OF THE INVENTION

According to the first aspect of the invention, there is provided a zoom optical system, comprising:

a stop, and

an optical element located on an object side of the zoom optical system with respect to said stop, wherein:

said optical element has at least one optical function surface, wherein said at least one optical function surface comprises a continuous surface and is constructed such that a line of intersection of a given reference plane with said optical function surface is configured such that there is a continuous change in at least a radius of curvature from one end toward another end, and

said optical element is rotated about a given axis of rotation, wherein:

said given reference plane is defined by a direction vector in a direction toward a distant object and a vector that passes through a center of said stop and is vertical to a stop plane, and said given axis of rotation is an axis that passes through a point that is not contiguous to said optical function surface within said given reference plane and is vertical to said given reference plane.

According to the second aspect of the invention, there is provided a zoom optical system, comprising:

a stop, and

an optical element located on an object side of the zoom optical system with respect to said stop, wherein:

said optical element has at least one optical function surface, wherein said at least one optical function surface comprises a continuous surface and is constructed such that a line of intersection of a given reference plane with said optical function surface is configured such that there is a continuous change in at least a radius of curvature from one end toward another end,

said optical element is rotated about a given axis of rotation, and

an image plane is fixed with respect to said stop or movable in a fixed plane, wherein:

said given reference plane is defined by a direction vector in a direction toward a distant object and a vector that passes through a center of said stop and is vertical to a stop plane, and said given axis of rotation is an axis that passes through a point that is not contiguous to said optical function surface within said given reference plane and is vertical to said given reference plane.

According to the third aspect of the invention, there is provided a zoom optical system, comprising:

a stop,

a first optical element located on an object side of the zoom optical system with respect to said stop, and

a second optical element located on an image side of the zoom optical system with respect to said stop, wherein:

said first optical element comprises at least one optical function surface, and

said second optical element comprises at least one optical function surface, wherein:

said at least one optical function surface of said first optical element comprises a continuous surface and is constructed such that a line of intersection of a given first reference plane with said optical function surface of said first optical element is configured such that there is a continuous change in at least a radius of curvature from one end toward another end, and

said at least one optical function surface of said second optical element comprises a continuous surface and is constructed such that a line of intersection of a given second reference plane with said optical function surface of said second optical element is configured such that there is a continuous change in at least a radius of curvature from one end toward another end,

said first optical element is rotated about a given first axis of rotation, and

said second optical element is rotated about a given second axis of rotation, wherein:

said given first reference plane for said first optical element is defined by a direction vector in a direction toward a distant object and a vector that passes through a center of said stop and is vertical to a stop plane, and said given first axis of rotation is an axis that passes through a point that is not contiguous to said optical function surface within said given first reference plane and is vertical to said given first reference plane, and

said given second reference plane for said second optical element is defined by a direction vector in a direction toward a distant object and a vector that passes through a center of said stop and is vertical to a stop plane, and said given second axis of rotation is an axis that passes through a point that is not contiguous to said optical function surface within said given second reference plane and is vertical to said given second reference plane.

According to the fourth aspect of the invention, there is provided a zoom optical system, comprising:

a stop,

a first optical element located on an object side of the zoom optical system with respect to said stop, and

a second optical element located on an image side of the zoom optical system with respect to said stop, wherein:

said first optical element comprises at least one optical function surface, and

said second optical element comprises at least one optical function surface, wherein:

said at least one optical function surface of said first optical element comprises a continuous surface and is constructed such that a line of intersection of a given first reference plane with said optical function surface of said first optical element is configured such that there is a continuous change in at least a radius of curvature from one end toward another end, and

said at least one optical function surface of said second optical element comprises a continuous surface and is constructed such that a line of intersection of a given second reference plane with said optical function surface of said second optical element is configured such that there is a continuous change in at least a radius of curvature from one end toward another end,

said first optical element is rotated about a given first axis of rotation while, at the same time,

said second optical element is rotated about a given second axis of rotation in the same direction as that of rotation of said first optical element, wherein:

said given first reference plane for said first optical element is defined by a direction vector in a direction toward a distant object and a vector that passes through a center of said stop and is vertical to a stop plane, and said given first axis of rotation is an axis that passes through a point that is not contiguous to said optical function surface within said given first reference plane and is vertical to said given first reference plane, and

said given second reference plane for said second optical element is defined by a direction vector in a direction toward a distant object and a vector that passes through a center of said stop and is vertical to a stop plane, and said given second axis of rotation is an axis that passes through a point that is not contiguous to said optical function surface within said given second reference plane and is vertical to said given second reference plane.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is illustrative in schematic of the fundamental arrangement of the zoom optical system according to the invention.

FIG. 2 is illustrative in schematic of the fundamental arrangement of the zoom optical system according to the invention, wherein two or more optical elements are rotated.

FIGS. 3(a), 3(b) and 3(c) are illustrative in section of the arrangements and optical paths at a wide-angle end (a), an intermediate setting (b) and a telephoto end (c) of the zoom optical system according to Example 1 of the invention.

FIG. 4 is a diagram for transverse aberrations at the wide-angle end of the optical system according to Example 1.

FIG. 5 is a diagram for transverse aberrations at the intermediate setting of the optical system according to Example 1.

FIG. 6 is a diagram for transverse aberrations at the telephoto end of the optical system according to Example 1.

FIG. 7 is illustrative of an image pickup zone upon zooming with respect to an image pickup range of an image pickup device used in Example 1.

FIG. 8 is illustrative of an image pickup zone upon zooming with respect to an image pickup range of another image pickup device used in Example 1.

FIGS. 9(a), 9(b) and 9(c) are illustrative in section of the arrangements and optical paths at a wide-angle end (a), an intermediate setting (b) and a telephoto end (c) of the zoom optical system according to Example 2 of the invention.

FIG. 10 is a diagram for transverse aberrations at the wide-angle end of the optical system according to Example 2.

FIG. 11 is a diagram for transverse aberrations at the intermediate setting of the optical system according to Example 2.

FIG. 12 is a diagram for transverse aberrations at the telephoto end of the optical system according to Example 2.

FIG. 13 is illustrative of one modified example of the decentered prism usable with the zoom optical system of the invention.

FIG. 14 is illustrative of another modified example of the decentered prism.

FIG. 15 is illustrative of yet another modified example of the decentered prism.

FIG. 16 is illustrative of a further modified example of the decentered prism.

FIG. 17 is illustrative of a further modified example of the decentered prism.

FIG. 18 is illustrative of a further modified example of the decentered prism.

FIG. 19 is illustrative of one example of the zoom optical system comprising a combination of prisms different from those of Examples 1 and 2 according to the invention.

FIG. 20 is illustrative of another example of the zoom optical system comprising a combination of prisms different from those of Examples 1 and 2 according to the invention.

FIG. 21 is illustrative of yet another example of the zoom optical system comprising a combination of prisms different from those of Examples 1 and 2 according to the invention.

FIG. 22 is illustrative of a further example of the zoom optical system comprising a combination of prisms different from those of Examples 1 and 2 according to the invention.

FIG. 23 is a front perspective view of the appearance of an electronic cameral on which the zoom optical system of the invention is mounted.

FIG. 24 is a rear perspective view of the electronic camera of FIG. 23.

FIG. 25 is a sectional view of the arrangement of the electronic camera of FIG. 23.

FIG. 26 is illustrative in conception of another electronic cameral on which the zoom optical system of the invention is mounted.

FIG. 27 is a front perspective view of a personal computer with a cover opened up, which incorporates the zoom optical system of the invention as an objective optical system.

FIG. 28 is a sectional view of a taking optical system in the personal computer.

FIG. 29 is a side view of the state of FIG. 27.

FIGS. 30(a) and 30(b) are a front view and a side view, respectively, of a cellular phone that incorporates the zoom optical system of the invention as an objective optical system, and FIG. 30(c) is a sectional view of a taking optical system therein.

FIG. 31(a) is illustrative of the arrangement of an electronic endoscope system on which the zoom optical system of the invention is mounted, and FIG. 31(b) is illustrative in conception of an optical system therein.

FIG. 32 is illustrative in conception of a presentation system on which the zoom optical system of the invention is mounted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The advantages of, and the requirements for, the above arrangements according to the invention are now explained.

In one preferable embodiment of the invention, at least one optical function surface comprising a reflecting or refracting surface (an optical element having an optical function surface) is located on an object side of the zoom optical system with respect to a stop, and that optical function surface is rotated about a point spaced away from that optical function surface. With such an arrangement, the position of light rays (light beam) that passes through the optical function surface (subjected to reflection or refraction) is varied for zooming. As a consequence, fewer optical elements can be used to achieve a zoom optical system at lower costs, and the stop remains so fixed in position that the associated stop mechanism can be more simplified.

More specifically, FIG. 1 is illustrative in schematic of the construction of the zoom optical system. With this zoom optical system, an image of a distant object O is formed on an image plane 3 with no formation of any intermediate image. Here let a vector A represent a direction vector in a direction from the zoom optical system toward the distant object (subject) O, and a vector B represent a direction vector that passes through the center of an aperture stop 2 in the optical system and is vertical to a stop plane. Then, a reference plane (Y-Z plane) is given by one plane defined by vectors A and B. The reference plane is found in the paper plane of FIG. 1, and the zoom optical system is symmetric with respect to that reference plane.

The zoom optical system comprises one or more optical elements 10 on its object side with respect to the stop 2. Each optical element 10 has at least one optical function surface. In the embodiment of FIG. 1, the optical element 10 comprises three optical function surfaces 11, 12 and 13 that form together one reflecting prism. However, it is noted that one or at least four optical function surfaces could be used. Although the optical function surface 12 is shown as a reflecting surface in FIG. 1, it is not necessarily limited thereto, and so a refracting surface could be used instead. The optical function surfaces 11 and 13 in FIG. 1 are refracting surfaces.

In this zoom optical system, the optical element 10 is rotated about the axis S of rotation (center axis) vertical to the reference plane. It follows that the zoom optical system is designed to perform zooming by rotation.

The optical function surface 12 is preferably configured as follows. First, the optical function surface 12 is preferably given by a continuous surface. The term "continuous surface", for instance, refers to a surface whose shape varies smoothly. Second, the optical function surface 12 is preferably given by a surface including zones with different radii of curvature. Referring here to this point, a line of intersection is created by the intersection of the reference plane with the optical function surface. As a matter of course, that line of intersection is included in the optical function surface 12. That line of intersection should then preferably be configured such that at least the radius of curvature (the radius of curvature in the paper plane of FIG. 1) changes continuously from one end to another end. In other words, the optical function surface must be given by the plane including such a line of intersection. For allowing the focal length of the optical system to change continuously, it is required that (1) the position of an axial chief ray 1 that crosses the optical function surface 12 be variable in association with rotation, and (2) the radius of curvature of the optical function surface 12 change continuously in a direction along the line of intersection. It is also desired that the radius of curvature in a direction vertical to the reference plane, too, changes continuously. It is here noted that the axial chief ray means a light ray that passes through the center of the stop 2 and arrives at the center of the image plane 3.

Here the axis S of rotation must be positioned at a point off the line of intersection (i.e., at a position that is not contiguous to the optical function surface 12 within the reference plane). This ensures that the point of the axial chief ray 1 crossing the optical function surface 12 changes in association with the rotation of the optical element 10. Especially with the axis S of rotation positioned away from that line of intersection, it is possible to largely change the position of the axial chief ray 1 crossing the optical function surface 12 and, hence, obtain a high zoom ratio.

Another line of intersection is created by the intersection of the reference plane with the optical function surface 11, and yet another line of intersection is created by the intersection of the reference plane with the optical function surface 13 as well. Of course, the axis S of rotation could be positioned on those lines of intersection (or, in another parlance, contiguous to the optical function surfaces 11 and 13 except the optical function surface 12). With the axis S of rotation positioned within or near the prism, the amount of movement of the prism could be reduced upon rotation.

Among possible surfaces configured such that their radii of curvature change continuously within one section as described above, there is a rotationally asymmetric surface represented by a free-form surface that is defined by the following formula (a). The Z-axis in this defining formula provides the axis of the free-form surface.

.times..times..times..times..times..times..times. ##EQU00001## Here the first term of formula (a) is a spherical term and the second term is a free-form surface term.

In the spherical term:

c is the curvature of the vertex, and

k is the conic (conical) coefficient,

r= {square root over ( )}(X.sup.2+Y.sup.2) r.

The free-form surface term is

.times..times..times..times..times..times..times..times..times..times..tim- es..times..times..times..times..times..times..times..times..times..times..- times..times..times..times..times..times..times..times..times..times..time- s..times..times..times..times..times..times..times..times..times..times..t- imes..times..times..times..times..times..times..times..times..times..times- . ##EQU00002## Here C.sub.j (j is an integer of 2 or greater) is a coefficient.

In general, the aforesaid free-form surface has no symmetric surface at both the X-Z plane and the Y-Z plane. However, by reducing all the odd-numbered terms for X to zero, that free-form surface can have only one symmetric surface parallel with the Y-Z plane. Likewise, by reducing all the odd-numbered terms for Y to zero, the free-form surface can have only one symmetric surface parallel with the X-Z plane.

Among other free-form surface defining formulae, there is Zernike polynomial given by the following formula (b) that defines the shape of this surface. The axis for Zernike polynomial is given by the Z-axis of the defining formula (b). The rotationally asymmetric surface is defined by polar coordinates for the height of the Z-axis with respect to the X-Y plane provided that R is the distance from the Z-axis within the X-Y plane and A is the azimuth angle around the Z axis, as expressed by the angle of rotation measured from the X-axis.

.times..times..times..times..times..times..times..times..times..times..tim- es..times..times..function..times..times..times..times..function..times..t- imes..times..function..times..times..function..times..times..times..functi- on..times..times..times..times..times..times..times..function..times..time- s..times..times..times..times..function..times..times..times..times..times- ..times..times..times..times..function..times..times..times..times..times.- .times..times..function..times..times..times..times..function..times..time- s..times..times..times..function..times..times..times..times..function..ti- mes..times..times..times..times..times..times..times..times..times..functi- on..times..function..times..times..times..times..times..times..times..func- tion..times..times..times..times..times..function..times..function..times.- .times..times..times..times..times..function..times..function..times..time- s..times..times..function..times..times..times..times..times..times..times- ..times..times..times..function..times..function..times..times..times..tim- es..times..times..times..function..times..times..times..times..times..func- tion..times..times..function..times..times..times..times..function..times.- .times..times..times..times..function..times..times..function..times..time- s..times..times..function..times..times..times..times..function..times. ##EQU00003##

Here D.sub.m (m is an integer of 2 or greater) is a coefficient. It is noted that when this free-form surface is designed in the form of an optical system symmetric in the X-axis direction, D.sub.4, D.sub.5, D.sub.6, D.sub.10, D.sub.11, D.sub.12, D.sub.13, D.sub.14, D.sub.20, D.sub.21, D.sub.22 . . . are used.

The aforesaid defining formulae are given for the purpose of illustrating surfaces of rotationally asymmetric curved shape, and so it is understood that the same effects are obtainable even with any other defining formula.

Given below is yet another free-form surface defining formula (c). Z=.SIGMA..SIGMA.C.sub.nmXY

Considering k=7 (the seventh term) as an example, the free-form surface upon expanded is represented as below.

.times..times..times..times..times..times..times..times..times..times..tim- es..times..times..times..times..times..times..times..times..times..times..- times..times..times..times..times..times..times..times..times..times..time- s..times..times..times..times..times..times..times..times..times..times..t- imes..times..times..times..times..times..times..times..times..times..times- . ##EQU00004##

An anamorphic surface, and a toric surface could also be used for the rotationally asymmetric surface.

Although not shown in FIG. 1, another optical element(s) having at least one optical function surface could be located on an image side of the zoom optical system with respect to the stop 2. At least one optical function surface (hereinafter called the optical function surface X) of that another optical element should preferably comprise a continuous surface. The optical function surface X should then preferably be constructed such that the line of intersection of the reference plane with the optical function surface X (hereinafter called the line X of intersection) is configured such that at least the radius of curvature changes continuously from one end to another end. It is also desired that the radius of curvature in a direction vertical to the reference plane changes continuously.

For that another optical element, it is desired to use an optical element having three or more optical function surfaces as is the case with the optical element 10 located on the object side of the zoom optical system with respect to the stop 2. It is then particularly preferable to use an optical element set up as a reflecting prism that may have four or more optical function surfaces given by either reflecting or refracting surfaces.

For zooming, another optical element is preferably rotated about an axis S' of rotation. In this case, if that another optical element is rotated in cooperation with the optical element 10, it is then possible to obtain much higher zoom ratios. It is noted that the axis S' of rotation is vertical to the reference plane, and positioned off the line X of intersection.

In an alternative embodiment of the invention, the image plane 3 is not fixed with respect to the stop 2. In other words, when the optical element on the object side with respect to the stop 2 (hereinafter referred to as the optical element F) and another optical element located on the image side with respect to the stop 2 (hereinafter referred to as the optical element R) are rotated, the image plane 3 is preferably moved in cooperation with that rotation.

In a further embodiment of the invention, the axial chief ray 1 incident on the first surface facing the object O (the optical function surface 11 in FIG. 1) could remain unfixed. For instance, the zoom optical system could be designed such that the axial chief ray 1 moves parallel in response to magnification changes.

Preferably, the image-formation optical system is also constructed such that upon zooming, the optical function surface positioned just before the stop (hereinafter called the optical function surface F) and the optical function surface positioned just after the stop (hereinafter called the optical function surface R) are rotated in mutually different directions with respect to the stop. Such being the arrangement, the axial chief ray passes through the center of the stop. Accordingly, there are obtained large changes in the position of the optical function surface R relative to the optical function surface F and, hence, large magnification changes.

For the optical element F, it is desired to have at least one reflecting surface. The rotation of the optical element takes space. If the optical element F has at least one reflecting surface, it is then possible to turn back an optical path; that is, it is possible for light rays to pass through the same space plural times. Accordingly, the efficiency of utilization of that space is improved, leading to size reductions of the optical system. The inclusion of at least one reflecting surface also reduces chromatic and other aberrations.

For the optical element F, it is also desired to have three or more surfaces. The inclusion of three or more surfaces makes the length of the optical path in the optical element so longer that there can be obtained a large change in the length of the optical path therein in association with rotation and, hence, more striking zoom effects can be obtained with fewer optical elements and more compact volumes.

The inclusion of three or more surfaces also ensures that some surfaces of the optical element F can be used as refracting surfaces. Allowing those surfaces to have refracting power ensures a large change in the power profile in the optical element in association with rotation. Accordingly, more striking zoom effects can be obtained with fewer optical elements and more compact volumes.

For the optical element F, it is further desired to have at least one rotationally asymmetric surface. Upon rotation of the optical element F, there are decentration aberrations. The decentration aberrations can be well minimized within the optical element F if it has at least one rotationally asymmetric surface.

Moreover for the optical element F, it is desired to satisfy the following condition (1) in terms of the angle of rotation upon zooming. 0.degree.<.theta.<120.degree. (1) Here .theta. is the angle of rotation of the optical element.

As the optical element is rotated at the angle of rotation that satisfies condition (1), it allows the length of the optical path in the optical element F and power profile to change largely. Accordingly, more striking zoom effects can be obtained with fewer optical elements and more compact volumes. As the upper limit of 120.degree. to condition (1) is exceeded, it causes light rays leaving the optical element F to fluctuate too largely. To avoid this, there is no choice but to increase the area of the optical function surface positioned on the exit side of the optical element F. This in turn causes the whole optical system to become unpreferably large. As the lower limit of 0.degree. is not reached, it renders optical path selection itself impossible; that is, it is impossible to change optical parameters.

More preferably, the following condition (1-1) should be satisfied. 5.degree.<.theta.<90.degree. (1-1)

At greater than the upper limit of 90.degree. to condition (1-1), much the same results as is the case with condition (1) are only obtained. At less than the lower limit of 5.degree., there is little zoom effect in association with rotation, or else there is no choice but to increase the amount of deformation of the optical function surface for the purpose of achieving zoom effects with the result that it is difficult to obtain performance by keeping back aberrations.

Even more preferably, the following condition (1-2) should be satisfied. 10.degree.<.theta.<60.degree. (1-2)

For the zoom ratio, it is preferable to satisfy the following condition (2). 1.01<.beta.<20 (2) Here .beta. is the zoom ratio.

As zooming takes place at the zoom ratio that satisfies condition (2), some significant zoom effects are achievable with performance kept intact. At greater than the upper limit of 20 to condition (2), the necessary angle of rotation becomes large, in turn causing light rays leaving the optical element F to fluctuate too largely. To avoid this, there is no option but to increase the area of the optical function surface positioned on the exit side of the optical element F. However, this renders the whole optical system un-preferably bulky. Otherwise, there is no option but to increase the amount of deformation of the shape of the optical function surface to obtain the desired zoom ratio. This is not preferable because it is difficult to obtain performance while aberrations are kept back. Falling short of the lower limit of 1.01 is not preferable because the zoom ratio becomes low.

More preferably, the following condition (2-1) should be satisfied. 1.5<.beta.<18 (2-1)

Even more preferably, the following condition (2-2) should be satisfied. 1.8<.beta.<16 (2-2)

It is further preferable to satisfy the following condition. 0<.nu..sub.max-.nu..sub.min<100 (3) Here .nu..sub.max is the maximum Abbe constant of an optical element included in the optical system, and .nu..sub.min is the minimum Abbe constant of an optical element included in the optical system.

The use of the optical elements (optical elements F and R) that satisfy condition (3) ensures that chromatic aberrations produced at the optical system are well reduced with fewer optical elements and compact volumes. There is no material that exceeds the upper limit of 100 to condition (3). As the lower limit of 0 is not reached, it means that the optical system is made up of only one material, or materials having quite the same Abbe constant. This is not preferable because of a failure in satisfactory reductions of chromatic aberrations.

More preferably, the following condition (3-1) should be satisfied. 5<.nu..sub.max-.nu..sub.min<100 (3-1)

There is no material that exceeds the upper limit of 100 to condition (3-1). Falling short of the lower limit of 5 is not preferable because there is too small a difference in the Abbe constant of the optical materials used, failing to satisfactorily hold back chromatic aberrations.

Even more preferably, the following condition (3-2) should be satisfied. 10<.nu..sub.max-.nu..sub.min<100 (3-2)

As described above, it is not always necessary to fix the image plane 3 with respect to the stop 2. In this respect, further reference is now made.

In another embodiment of the zoom optical system of the invention, the image plane 3 could be fixed with respect to the fixed stop 3 or movable within a fixed plane. As the image plane 3 remains fixed or is movable in the fixed plane, it makes unnecessary to move a light-receiving portion of an image pickup device or the like located at the image plane. Accordingly, that light-receiving portion can be simplified in construction with the consequence that the zoom optical system can be made compact.

As described above, one or more separate optical elements could be located on the image side with respect to the stop 2. In this respect, further reference is now made.

In yet another embodiment of the zoom optical system of the invention, optical elements could be located on the object and image sides with respect to the stop, at least one on each side. Each optical element has optical function surfaces comprising reflecting or refracting surfaces. Those optical function surfaces are rotated about a point off them, so that the positions of light rays (light beam) passing through them (subjected to reflection or refraction) can be changed for zooming. Consequently, a more compact zoom optical system is achievable with fewer optical elements and at lower costs. In addition, since the stop remains fixed in position, the stop mechanism can be more simplified.

Even with one optical element adapted to rotate with respect to the image plane, zoom effects may be obtainable. However, the image point position is displaced in association with rotation. Rotation of the optical element is somehow achievable with no displacement of the image point position. However, attempts to have high zoom ratios render surface shape complicated, resulting in difficulty with which satisfactory optical performance is obtainable. Otherwise, it is required to increase optical element size to obtain satisfactory optical performance or to use some mechanisms for non-rotational movements. However, allowing two or more optical elements to rotate prevents displacement of the image point position, and makes it possible to obtain more striking zoom effects with fewer optical elements and compact volumes.

Referring more specifically to FIG. 2 that is illustrative in schematic of the construction of the zoom optical system, it is adapted to form an image of a distant object O on an image plane 3 with no formation of any intermediate image. Here let a vector A represent a direction vector in a direction from this optical system toward a distant object (subject) O, and a vector B stand for a direction vector that passes through the center of an aperture stop 2 in the optical system and is vertical to a stop plane. In the invention, one plane defined by the vectors A and B is referred to as a reference plane (Y-Z plane) that lies in the paper plane of FIG. 2. The zoom optical system is symmetric with respect to this reference plane.

In the zoom optical system, optical elements 10 and 20 having at least one optical function surface are located on the object and image sides thereof with respect to the stop 2, at least one on each side. In FIG. 2, the optical element 10 on the object side with respect to the stop 2 comprises three optical function surfaces 11, 12 and 13 that form together one reflecting prism. The optical element 20 on the image side with respect to the stop 2, too, comprises three optical function surfaces 21, 22 and 23 that form together one reflecting prism. However, each optical element 10, 20 could have one, or four or more optical function surfaces. Although the optical function surface 12 is shown as a reflecting surface in FIG. 2, it is not necessarily limited thereto, and so a refracting surface could be used instead. The optical function surfaces 11, 13, 21 and 23 in FIG. 2 are refracting surfaces.

In this zoom optical system, the optical element 10 is rotated about the axis Si of rotation (center axis) vertical to the reference plane, and in association with this, the optical element 20 is rotated about the axis S2 of rotation (center axis) vertical to the reference plane, too. It follows that the zoom optical system is designed to perform zooming by rotation of two optical elements 10 and 20.

The optical function surface 12, 22 is preferably configured as follows. First, the optical function surface 12, 22 is preferably given by a continuous surface, as already defined.

Here the axis S1, S2 of rotation must be positioned at a point off the line of intersection (i.e., at a position that is not contiguous to the optical function surface 12, 22 within the reference plane). This ensures that the point of the axial chief ray 1 crossing the optical function surface 12, 22 changes in association with the rotation of the optical element 10, 20.

Especially with the axis S1, S2 of rotation positioned away from that line of intersection, it is possible to largely change the position of the axial chief ray 1 crossing the optical function surface 12, 22 and, hence, obtain a high zoom ratio.

Thus, allowing two or more optical elements 10, 20 to rotate in operable association ensures that more striking zoom effects are achievable with fewer optical elements and more compact volumes yet with no displacement of the image plane 3.

Another line of intersection is created by the intersection of the reference plane with the optical function surface 11, 21, and yet another line of intersection is created by the intersection of the reference plane with the optical function surface 13, 23. Of course, the axis S1, S2 of rotation could be positioned on those lines of intersection (or, in another parlance, contiguous to the optical function surfaces 11, 13, 21 and 23 except the optical function surfaces 12 and 22). With the axis S1, S2 of rotation positioned within or near the prism 10, 20, the amount of movement of the prism could be reduced upon rotation of the prism.

In the instant embodiment of the invention, the optical element 10 on the object side with respect to the stop 2 and another optical element 20 on the image side with respect to the stop 2 are rotated for zooming purposes. The image-formation optical system is then preferably constructed such that the optical function surface 13 positioned right before the stop 2 and the optical function surface 21 positioned right after the stop 2 are rotated in mutually different directions relative to the stop 2. Such being the arrangement, the axial chief ray 1 passes through the center of the stop 2, so that the position of the optical function surface 21 can be largely changed relative to the optical function surface 13 with the result that there can be large magnification changes. It is here noted that the optical function surfaces 12 and 21 mean non-planar surfaces.

For the optical element 10, 20, it is desired to have at least one reflecting surface. The rotation of the optical element takes space. If the optical element 10, 20 has at least one reflecting surface, it is then possible to turn back an optical path; that is, it is possible for light rays to pass through the same space plural times. Accordingly, the efficiency of utilization of that space is improved, leading to size reductions of the optical system. The inclusion of at least one reflecting surface also holds back chromatic and other aberrations.

For the optical element 10, 20, it is also desired to have three or more surfaces. The inclusion of three or more surfaces makes the length of the optical path in the optical element so longer that there can be obtained a large change in the length of the optical path therein in association with rotation and, hence, more striking zoom effects can be obtained with fewer optical elements and more compact volumes.

The inclusion of three or more surfaces also ensures that some surfaces of the optical element 10, 20 can be used as refracting surfaces. Allowing those surfaces to have refracting power ensures a large change in the power profile in the optical element in association with rotation. Accordingly, more striking zoom effects can be obtained with fewer optical elements and more compact volumes.

For the optical element 10, 20, it is further desired to have at least one rotationally asymmetric surface. Upon rotation of the optical element 10, 20, there are decentration aberrations. The decentration aberrations can be well minimized within the optical element 10, 20 if it has at least one rotationally asymmetric surface.

The aforesaid conditions (1), (1-1), (2), (2-1), (3), (3-1) and (3-2) also hold true for the zoom optical system comprising the optical elements 10 and 20. For instance, the optical element 20, let alone the optical element 10, should preferably satisfy conditions (1) and (1-1). The optical elements F and R in the foregoing explanation of the conditions correspond to the optical elements 10 and 20, respectively.

The optical element 10 and the optical element 20 could be rotated as follows.

The zoom optical system is designed in such a way as to include two or more rotating optical elements with the stop sandwiched between them, wherein both optical elements are rotated in the same direction. Such being the arrangement, two optical function surfaces positioned with the stop interposed between them move in mutually opposite directions, so that even with lesser amounts of rotation, higher zoom ratios are achievable while aberrations are well kept back.

Referring specifically to FIG. 2, two or more optical elements 10 and 20 are rotated in cooperation, as indicated by an arrow, so that zooming can be carried out with no displacement of the position of the image plane 3. In this case, the optical function surfaces 13 and 21 opposing with the stop 2 interposed between them (refracting surfaces in FIG. 2) move in mutually opposite directions. Accordingly, zooming can take place with lesser amounts of rotation even at the same zoom ratio, because the amount of relative movement becomes larger than that of movement of either one of the optical elements. The result is that even with lesser amounts of rotation, higher zoom ratios are achievable while aberrations are well kept back. It is also possible to obtain more striking zooming effects with fewer optical elements and more compact volumes.

The electronic equipment of the invention preferably comprises each of the optical systems described so far and an electronic image pickup device located on the image side thereof. Each optical system is a compact, slimmed-down, low-cost one. Therefore, if such an optical system is incorporated in the electronic equipment as an image pickup optical system, it is then possible to reduce the size, thickness and cost of the electronic equipment. The electronic equipment, for instance, includes digital cameras, video cameras, digital video units, personal computers, mobile computers, cellular phones, personal digital assistants, and electronic endoscopes.

Preferably, the electronic equipment comprises means for electrically correcting the shape of an image formed through the zoom optical system. This zoom optical system is susceptible to produce rotationally asymmetric image distortions varying with magnifications and chromatic aberrations. When it is intended to make good correction for such aberrations by the optical system, there is an increase in the number of optical elements and, hence, an increase in the size of the optical system. Therefore, portions of the aberrations left undercorrected at the optical system are electrically corrected. This is preferable because the optical system can be made more compact.

That correction is preferably carried out using a different parameter for each wavelength area, with a table having a different correction parameter for each focal length.

Specific examples of the zoom optical system (image pickup optical system) of the invention are now explained with reference to the accompanying drawings.

The construction parameters of each example will be set forth later. For instance, as shown in the sectional views of FIG. 3, an axial chief ray 1 is defined by a light ray vertically incident on the first surface of the optical system located nearest to the object side (in FIG. 3, the first surface CG1a of a cover glass CG1), passing the center of a stop 2 in the optical system and arriving at the center of an image plane 3, as viewed in normal ray tracing. A position at which the first surface of the optical system located nearest to the object side (in FIG. 3, the first surface CG1a of the cover glass CG1) crosses the axial chief ray 1 at a wide-angle end is defined as the origin of a decentered optical element in the decentered optical system. A direction along the axial chief ray 1 is defined as the Z-axis direction, and a direction from an object toward the first surface is defined as the Z-axis positive direction. A plane at which the optical axis is bent is defined as the Y-Z plane, and a direction orthogonal to the Y-Z plane through the origin is defined as the X-axis direction. A direction coming in the paper of FIG. 3 is defined as the X-axis positive direction, and the axis forming a right hand system with the X- and Z-axes is defined as the Y-axis.

In Example 1 and Example 2, each surface (optical function surface) is decentered in the Y-Z plane, and only one symmetric plane of each rotationally asymmetric free-form surface is defined as the Y-Z plane.

Given for a decentered surface are the amount of decentration of the vertex of that surface from the center of the origin of the optical system (X, Y and Z standing for the amounts of shift in the X, Y and Z-axis directions) and the angles (.alpha., .beta., .gamma.(.degree.)) of tilt of the center axis (the Z axis in the following formula (a) for a free-form surface) with respect to the X-axis, the Y-axis, and the Z-axis, respectively. It is here noted that the positive .alpha. and .beta. mean counterclockwise rotation with respect to the positive directions of the respective axes, and the positive .gamma. means clockwise rotation with respect to the positive direction of the Z-axis. Regarding how to perform rotation .alpha., .beta. and .gamma. about the center axis of the surface,