Compact zoom lens

Details Compact zoom lens Compact zoom lens

2000-06-30

2002-05-21

Sugarman, Scott J. (Department: 2873)

Optical: systems and elements

Lens

With variable magnification

Reexamination Certificate

active

06392818

ABSTRACT:

RELATED APPLICATIONS
This application claims the priority of Japanese Patent Application No. 11-189833 filed on Jul. 5, 1999, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a compact zoom lens; and, in particular, to a low-cost, compact zoom lens suitable for a lens shutter camera.
2. Description of the Prior Art
Demands for higher magnification, compactness, and lower cost have been increasing for lens systems employed in lens shutter cameras in recent years. For responding to these various demands, utilization of aspheric surfaces, use of special glass materials, arrangement of shutter position, and the like have actively been proposed.
Known as such a zoom lens are three-group zoom lenses disclosed in Japanese Unexamined Patent Publication Nos. 4-78811 and 7-20380, for example. Each of these zoom lenses comprises three groups having positive, positive, and negative refracting powers successively from the object side, and achieves a power variation ratio of about 2 to 3.5.
In recent years, however, there have been demands for further higher magnification, and further smaller size and lower cost than those of the above-mentioned prior art.
SUMMARY OF THE INVENTION
In view of such circumstances, it is an object of the present invention to provide a low-cost, compact zoom lens having a high magnification with a zoom ratio of about 4.
The present invention provides a compact zoom lens comprising, successively from an object side, a first lens group having a positive refracting power, a second lens group having a positive refracting power, and a third lens group having a negative refracting power, air spaces among the lens groups being variable so as to change a magnification;
wherein the second lens group comprises, successively from the object side, a negative meniscus lens having a concave surface directed onto the object side, a positive biconvex lens, and a positive meniscus lens having at least one aspheric surface and a concave surface directed onto the object side.
Preferably, the third lens group comprises, successively from the object side, a plastic-made meniscus lens, whose both surfaces are aspheric, having a relatively weak refracting power, and a negative meniscus lens having a concave surface directed onto the object side.
Preferably, the compact zoom lens satisfies the following conditional expressions (1) and (2):
4.5<
f
T
/fG
2
<7.0  (1)
fG
2
/fG
3
<−0.8  (2)
where
f
T
is the focal length on the longer focus side;
fG
2
is the focal length of the second lens group; and
fG
3
is the focal length of the third lens group.
Preferably, a stop is disposed on an imaging surface side from the first lens group, and the air space between the first lens group and the stop is held constant when changing the magnification.
The present invention also provides a lens shutter camera comprising the compact zoom lens.


REFERENCES:
patent: 6064531 (2000-05-01), Ishii et al.
patent: 6075654 (2000-06-01), Toyama
patent: 6307684 (2001-10-01), Iyama
Japanese Patent Office, Patent Abstracts of Japan, Publication No. 7020380, Date of Publication; Jan. 24, 1995, Application No: 5-309575, Date of Filing: Dec. 10, 1993.
Japanese Patent Office, Patent Abstracts of Japan, Publication No. 04078811 A, Date of Publication: Mar. 12, 1992, Application No: 02193285, Date of Filing, Jul. 20, 1990, pp. 115-137. (English translation of Abstract).

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