Variable focal length lens system

Details Variable focal length lens system Variable focal length lens system

2000-08-01

2001-10-16

Nguyen, Thong (Department: 2872)

Optical: systems and elements

Lens

With variable magnification

C359S676000, C359S708000

Reexamination Certificate

active

06304389

ABSTRACT:

This application claims the benefit of Japanese Application No. 11-220000 which is hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to a variable focal length lens system and, in particular, to a variable focal length lens system having a zoom ratio of 2.5 or over, a field angle of 60° or over at the wide-angle end, and an excellent imaging quality which is suited for use with a video camera or a digital still camera employing a solid-state imaging device and the like.
BACKGROUND OF THE INVENTION
Variable focal length lens systems suitable for use with a solid-state imaging device have been disclosed in the Japanese Patent Laid-Open Publication No. 6-94996 and in the Japanese Patent Laid-Open Publication No.7-261083, etc.
Every one of embodiments disclosed in the Japanese Patent Laid-Open Publication No. 6-94996, however, has a zoom ratio such as about 2, and it is not sufficient.
In each embodiment disclosed in the Japanese Patent Laid-Open Publication No. 7-261083, the zoom ratio is about 2.3, and it is still not sufficient. Further, a variation of spherical aberration in accordance with zooming is large and imaging quality is not sufficient as shown in aberration charts disclosed in the publication.
SUMMARY OF THE INVENTION
The present invention is made in view of aforementioned problems, and has an object to provide a variable focal length lens system having a zoom ratio of 2.5 or over, a field angle of 60° or over at the wide-angle end, and an excellent imaging quality which is suited for use with a video camera or a digital still camera employing solid-state imaging device and the like.
In order to solve the problems, a variable focal length lens system according to the present invention has; in order from an object side, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power; wherein the first lens group includes, in order from the object side, a lens unit
1
-
1
having negative refractive power and a lens unit
1
-
2
having positive refractive power separated by predetermined air space; and wherein the second lens group includes, in order from the object side, a lens unit
2
-
1
having positive refractive power, a lens unit
2
-
2
having negative refractive power separated by predetermined air space, and a lens unit
2
-
3
having positive refractive power separated by predetermined air space; wherein the first and second lens groups are moved such that when a state of the lens group positions is changed from a wide-angle end state (a state providing the shortest focal length of the lens system) to a telephoto end state (a state providing the longest focal length of the lens system), a space between the first and second lens groups is decreased and a space between the second and third lens groups is increased while the third lens group is fixed; and wherein the following conditions is satisfied:
0.7 < f2 / |f1| < 1.5
(f1 < 0)
(1)
3 < f3 / fw < 10
(2)
1 < f12 / |f1| < 3
(f1 < 0)
(3)
1 < |f22| / f2 < 5
(f22 < 0)
(4)
1.6 < (D1w − D1t) / fw < 6
(5)
1.6 < (D2t − D2w) / fw < 6
(6)
where f
1
denotes the focal length of the first lens group, f
2
denotes the focal length of the second lens group, f
3
denotes the focal length of the third lens group, fw denotes the focal length of the lens system at the wide-angle end state, f
12
denotes the focal length of the lens unit
1
-
2
, f
22
denotes the focal length of the lens unit
2
-
2
, D
1
w denotes the space between the first lens group and the second lens group at the wide-angle end state, D
1
t denotes the space between the first lens group and the second lens group at the telephoto end state, D
2
w denotes the space between the second lens group and the third lens group at the wide-angle end state, and D
2
t denotes the space between the second lens group and the third lens group at the telephoto end state.


REFERENCES:
patent: 5262897 (1993-11-01), Kawamura
patent: 5434710 (1995-07-01), Zozawa
patent: 5550679 (1996-08-01), Sugawara
patent: 5909318 (1999-06-01), Tanaka
patent: 6-94996 (1994-04-01), None
patent: 7-261083 (1995-10-01), None

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