Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
1999-05-19
2001-01-30
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S708000
Reexamination Certificate
active
06181484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a compact two-group wide-angle zoom lens for a lens shutter camera, which covers a wide angle area by two lens groups.
2. Related Background Art
Recently, as a lens system used for lens shutter cameras, that loaded with a zoom lens has been becoming the mainstream. Since such a zoom lens requires its compactness in the first place, there has been put into practice a two-group zoom lens with a telephoto type of refracting power arrangement, comprising a first lens group with a positive refracting power and a second lens group with a negative refracting power.
Further, there have been known various configurations in which an aspheric surface is used for a lens surface so as to reduce the number of lens sheets, while improving optical performances.
As such art, commonly-assigned Japanese Unexamined Patent Publication No., 9-101454 (Japanese Patent Application No. 7-284551) discloses a technique which can also restrain refractive index from fluctuating upon changes in a plastic lens with respect to temperature.
In the above-mentioned technique, however, since a lens shutter is disposed between the first and second lens groups, which change the distance therebetween upon zooming, it is necessary for these lens groups to secure a considerable amount of distance therebetween when they are moved to the telephoto end. Here, it is thus difficult for the whole lens thickness to be greatly reduced.
SUMMARY OF THE INVENTION
In view of such circumstances, it is an object of the present invention to provide a compact two-group wide-angle zoom lens which can greatly reduce the whole lens thickness when the lens system is positioned at its telephoto end and yield more compactness, while maintaining favorable optical performances.
The compact two-group wide-angle zoom lens in accordance with the present invention consisting, successively from an object side, a positive first lens group G
1
having at least one aspheric surface and a negative second lens group G
2
, in which a distance between said lens groups is changed to attain a variable power;
wherein said first lens group G
1
is composed of G
1
A group and G
1
B group;
wherein a stop is disposed between said G
1
A and G
1
B groups; and
wherein said zoom lens satisfies the following conditional expressions:
−0.6<f′w/f′g1a<1.4 (1)
0.07<Dab/f′w<0.25 (2)
wherein:
f′w is the rear-side focal length of the whole lens system at the wide-angle end;
f′g1a is the focal length of the G
1
A group;
Dab is the air space between the G
1
A group and the G
1
B group.
Further, the compact two-group wide-angle zoom lens in accordance with the present invention consisting, successively from an object side, a positive first lens group G
1
having at least one aspheric surface and a negative second lens group G
2
, in which a distance between the lens groups is changed to attain a variable power;
wherein the first lens group G
1
is composed of G
1
A group comprising, successively from the object side, a negative lens having a meniscus form with a concave surface directed onto the object side and a positive lens having a meniscus form with a convex surface directed onto the object side, and G
1
B group having at least one biconvex lens;
wherein the second lens group G
2
comprises, successively from the object side, a meniscus lens having an aspheric surface with a concave surface directed onto the object side, a positive lens having a convex surface directed onto the object side, and a negative lens having a concave surface directed onto the object side;
wherein a stop is disposed between the G
1
A and G
1
B groups; and
wherein the zoom lens satisfies the following conditional expressions:
−0.6<f′w/f′g1a<1.4 (1)
0.07<Dab/f′w<0.25 (2)
wherein:
f′w is the rear-side focal length of the whole lens system at the wide-angle end;
f′g1a is the focal length of the G
1
A group;
Dab is the air space between the G
1
A group and the G
1
B group.
REFERENCES:
patent: 5493448 (1996-02-01), Betensky et al.
patent: 9101454 (1997-04-01), None
Epps Georgia
Fuji Photo Optical Co., Ltd.
Schwartz Jordan M.
Snider Ronald R.
Snider & Associates
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