Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2002-05-16
2004-04-06
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S683000
Reexamination Certificate
active
06717741
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a zoom lens, and more particularly to a two-group zoom lens system which is used on a compact camera for instance.
So-called zoom lenses for compact cameras have some considerable limitations imposed on their zoom ratios and aperture ratios. So far, two-group zoom lenses of simple construction having positive refracting power and negative refracting power have been known for those having a relatively low zoom ratio.
Such two-group zoom lenses, for instance, are disclosed in U.S. Pat. No. 5,825,557 and JP-A 10-161025. In one two-group zoom lens embodiment, a negative meniscus lens having concave on its object side is located on the side of the positive first lens group nearest to the object side and the negative second lens group comprises a negative, a positive and a negative lens.
In the state-of-the art in such two-group zoom lenses, however, the amount of movement of each lens group for zooming is still large. A technical challenge to ensuring image-formation capabilities and achieving considerable reductions in the overall length of the lens system is virtually untapped at present. Nor are any satisfactory results obtained.
Most of actual zoom lenses for compact cameras have a mechanism capable of receiving them in an associated camera body, regardless of their zoom types. To this end, a collapsing mechanism is provided in a space at the wide-angle end wherein the zoom lens becomes shortest.
When the camera is actually used, on the other hand, the zoom lens is used at its original optical layout. In the case of a high-magnification zoom lens, the amount of zooming movement becomes large on the telephoto side. This in turn causes the lens barrel to become very long, offering a center-of-gravity shift problem and hence a decentration problem.
SUMMARY OF THE INVENTION
In view of the state of the art in such a two-group type zoom lens of +− construction, an object of the present invention is to provide a zoom lens system which, albeit having a high zoom ratio, has a short overall length not only at its wide-angle end but also at its telephoto end and a low telephoto ratio at the telephoto end where the overall length becomes longest, so that when it is used on a camera, the size of the camera can be reduced.
In order to accomplish the aforesaid object, the present invention provides a zoom lens system comprising, in order from an object side thereof, a first lens group having positive refracting power and a second lens group having negative refracting power, characterized in that
for zooming from a wide-angle end to a telephoto end of said system, each lens group moves toward said object side while a spacing between said first lens group and said second lens group becomes narrow, and said system satisfies the following conditions:
0.02
<|f
2
|/f
T
<0.35 (1)
0.30
<&Dgr;X
2T
/f
T
<0.58 (2)
2.25<&bgr;
2T
/&bgr;
2W
<5.0 (3)
where f
2
is a focal length of said second lens group, f
T
is a focal length of said zoom lens system at said telephoto end, &Dgr;X
2T
is an amount of zooming of said second lens group to said telephoto end as measured on a wide-angle end basis, &bgr;
2T
is a transverse magnification of said second lens group at said telephoto end, and &bgr;
2W
is a transverse magnification of said second lens group at said wide-angle end.
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.
REFERENCES:
patent: 5029994 (1991-07-01), Aoki
patent: 5459616 (1995-10-01), Kawamura et al.
patent: 5687027 (1997-11-01), Itoh
patent: 5825557 (1998-10-01), Ohno
patent: 5995299 (1999-11-01), Yoon
patent: 6008953 (1999-12-01), Itoh
patent: 6081390 (2000-06-01), Konno
patent: 6384986 (2002-05-01), Nishimura
Patent Abstracts of Japan, Jun. 1998, Pub. No. 10161025, Appln. No. 08334990, Nov. 1996, Kenichi Sato.
Olympus Corporation
Schwartz Jordan M.
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