Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2001-02-26
2003-05-06
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S689000
Reexamination Certificate
active
06560035
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a three-lens-group zoom lens system for a compact camera, and in particular, relates to increasing the zoom ratio of such a zoom lens system.
2. Description of the Related Art
In a zoom lens system for a compact camera, a long back focal distance is not necessary, unlike a zoom lens system of a single lens reflex (SLR) camera which requires a space to provide a mirror behind the lens system. Therefore in a compact camera, a telephoto-type lens system, including a positive lens group and a negative lens group, in this order from the object, is generally used. On the other hand, in a single lens reflex camera, a retrofocus-type lens system, including a negative lens group and a positive lens group, in this order from the object, is used.
In a compact camera, the zoom ratio of the telephoto-type zoom lens system is conventionally at most 2 to 3 in the case of the three-lens-group arrangement. Moreover, a three-lens-group zoom lens system having a zoom ratio of 4.0 or more has not been known.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a three-lens-group zoom lens system for a compact camera, which can attain a high zoom ratio of 4.0 or more.
In order to achieve the above-mentioned object, there is provided a zoom lens system including a negative first lens group, a positive second lens group, and a negative third lens group, in this order from the object. Zooming is performed by moving the first through third lens groups in the optical axis direction. The negative first lens group includes positive-and-negative cemented lens elements in which the most object-side surface is a concave surface. The zoom lens system satisfies the following conditions:
−1<r
1
/
fW
<0 (1)
1.4<f
1
G/f
1
N<1.8 (2)
wherein
r
1
designates the radius of curvature of the most object-side surface of the negative first lens group;
fW designates the focal length of the entire zoom lens system at the short focal length extremity;
f
1
G designates the focal length of the negative first lens group; and
f
1
N designates the focal length of the negative lens element of the cemented lens elements of the negative first lens group.
In the cemented lens elements, the order of the positive lens element and the negative lens element is not specifically required. Accordingly, the cemented lens elements can be constituted by the negative lens element and the positive lens element in this order from the object.
The zoom lens system according to the present invention preferably satisfies the following condition:
8
<&ngr;n−vp
(3)
wherein
&ngr;n designates the Abbe number of the negative lens element of the cemented lens elements of the negative first lens group; and
&ngr;p designates the Abbe number of the positive lens element of the cemented lens elements of the negative first lens group.
The zoom lens system according to the present invention can satisfy the following condition:
−5
<fT
/f
1
G<−3.5 (4)
wherein
fT designates the focal length of the entire zoom lens system at the long focal length extremity.
The zoom lens system according to the present invention preferably satisfies the following condition:
0.03<(d
12
W−d
12
T)/
fW<
0.10 (5)
wherein
d
12
W designates the distance between the first lens group and the second lens group at the short focal length extremity; and
d
12
T designates the distance between the first lens group and the second lens group at the long focal length extremity.
The zoom lens system according to the present invention can satisfy the following condition:
0.6
<y/fW<
0.9 (6)
wherein
y designates the diagonal image heighton a film surface.
The zoom lens system according to the present invention preferably satisfies the following condition:
3.5
<fT/fW
(7)
The zoom lens system according to the present invention can attain a zoom ratio of 4 or more. On the other hand, the zoom lens system of the present invention can also be applied to a zoom lens system having a zoom ratio of about 3.5.
In the zoom lens system of the present invention, it is preferable that a lens element having at least one aspherical surface be provided in the positive second lens group, and the following condition be satisfies:
−30
<&Dgr;IASP<−
10 (8)
wherein
&Dgr;IASP designates the amount of change of the spherical aberration coefficient due to the aspherical surface under the condition that the focal length of the entire zoom lens system at the short focal length extremity is converted to 1.0.
Furthermore, in the zoom lens system of the present invention, it is preferable that a lens element having at least one aspherical surface be provided in the negative third lens group, and the following condition be satisfied:
0<
&Dgr;VASP<
0.4 (9)
wherein
&Dgr;VASP designates the amount of change of the distortion coefficient due to the aspherical surface under the condition that the focal length of the entire zoom lens system at the short focal length extremity is converted (normalized) to 1.0.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2001-015741 (filed on Jan. 24, 2001) which is expressly incorporated herein by reference in its entirety.
Copending and commonly assigned U.S. Patent Application to “A Zoom Lens System”, listing as an inventor Takashi ENOMOTO, filed concurrently with the present application, having Attorney docket No. P20342; and Japanese Patent Application No. 2000-047619 (filed on Feb. 24, 2000), from which the application designated by Attorney docket No. P20342 claims priority, are expressly incorporated herein by reference in their entireties.
REFERENCES:
patent: 4917482 (1990-04-01), Ito
patent: 4984877 (1991-01-01), Ito
patent: 5572276 (1996-11-01), Hirakawa
patent: 5585970 (1996-12-01), Shibayama
patent: 5793535 (1998-08-01), Ito et al.
patent: 6028714 (2000-02-01), Koyama
patent: 8-146296 (1996-06-01), None
Greenblum & Bernstein P.L.C.
Pentax Corporation
Sugarman Scott J.
LandOfFree
Zoom lens system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Zoom lens system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Zoom lens system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3012459