Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2000-02-15
2001-11-13
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S680000
Reexamination Certificate
active
06317271
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens system in which the angle-of-view at the short focal length extremity is about 52°, and the angle-of-view at the long focal length extremity is about 28°.
2. Description of the Related Art
As a conventional zoom lens system, for a 35 mm camera, covering a semi-standard wide-angle range over an intermediate telephoto range, a zoom lens system in which the F-number is 4 and the focal length range is about 28 mm to 80 mm is already known; however, a focal length on the telephoto side is short and the F-number is larger. Further, a zoom lens system in which the F-number is 2.8 which is slightly smaller than 4, and the focal length range is about 28 mm to 70 mm is also known; however, a focal length on the telephoto side is much shorter.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a miniaturized and high-optical-performance zoom lens system which has a large aperture, and in which the focal length at the long focal length extremity is made long though the focal length at the short focal length extremity cannot be made short. More concretely, it is an object of the present invention to provide a high-optical performance zoom lens system in which the F-number is about 2.8, and the focal length range about 45 mm to 90 mm.
A zoom lens system according to the present invention includes a negative first lens group, a positive second lens group, a negative third lens group and a positive fourth lens group, in this order from the object. The zoom lens system satisfies the following conditions:
4<fL/D1<6 (1)
1.0<|fL/f1|<1.3 (2)
wherein
fL designates the focal length of the entire zoom lens system at the long focal length extremity;
D1 designates the distance, along the optical axis, from the most object-side to the most image-side lens surfaces of the first lens group; and
f1 designates the focal length of the first lens group.
The second lens group preferably satisfies the following condition:
1.5<fL/f2<2.5 (3)
wherein
f2 designates the focal length of the second lens group.
The second lens group through the fourth lens group preferably satisfy the following conditions:
1.0<|f2/f3|<1.5 (4)
1.7<fL/f4<2.5 (5)
wherein
f3 designates the focal length of the third lens group; and
f4 designates the focal length of the fourth lens group.
The present disclosure relates to subject matter contained in Japanese Patent Application No.Hei 11-39988 (filed on Feb. 18, 1999) which is expressly incorporated herein by reference in its entirety.
REFERENCES:
patent: 4516839 (1985-05-01), Tokumaru
patent: 6075653 (2000-06-01), Narimatsu et al.
patent: 2080966 (1982-02-01), None
patent: 54151027 (1979-11-01), None
patent: 55-14403 (1980-04-01), None
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Schwartz Jordan M.
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