Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2002-09-17
2004-08-03
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S691000, C359S740000
Reexamination Certificate
active
06771430
ABSTRACT:
The disclosures of the following priority applications are herein incorporated by reference:
Japanese Patent Application No. 2001-304454 filed Sep. 28, 2001; and
Japanese Patent Application No. 2001-304524 filed Sep. 28, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a compact zoom lens system having a zoom ratio about two to four, a small amount of chromatic aberration, and high optical performance across the entire image, suitable for a video camera and an electronic still camera using an imaging device such as a solid state imaging device.
2. Related Background Art
A lot of zoom lens systems suitable for a video camera and an electronic still camera using an imaging device such as a solid state imaging device have been proposed. Among them, the majority of the zoom lens systems having a zoom ratio about two to four is a zoom lens type having a negative lens to the most object side of the lens system. For example, there is a zoom lens system disclosed in Japanese Patent Application Laid-Open No. 11-23967.
In recent years, the number of image pixels used in a video camera and an electronic still camera using an imaging device such as a solid state imaging device has steadily been increasing. In accordance with the trend, the lens system has been requested to have higher optical performance across the entire image. In particular, the lens system has been requested to reduce flare component and chromatic aberration as well as have high optical performance in the periphery.
However, the zoom lens systems disclosed in Japanese Patent Application Laid-Open No. 11-23967 and the like have had a problem not to have sufficient ability to reduce flare component or chromatic aberration across the entire image.
SUMMARY OF THE INVENTION
The present invention is made in view of the aforementioned problem and has an object to provide a zoom lens system having a zoom ratio about two to four, a small amount of chromatic aberration, and high optical performance across the entire image, suitable for a video camera and an electronic still camera using an imaging device such as a solid state imaging device.
According to one aspect of the present invention, a zoom lens system includes, in order from an object along an optical axis, a first lens group G
1
having negative refractive power, and a second lens group G
2
having positive refractive power. A distance between the first lens group G
1
and the second lens group G
2
decreases when the state of lens group positions varies from a wide-angle end state W to a telephoto end state T. The second lens group G
2
is composed of, in order from the object, a first lens U
21
having positive refractive power, a first cemented lens U
22
having negative refractive power, and a second cemented lens U
23
having positive refractive power. The first cemented lens U
22
in the second lens group G
2
is constructed by a positive lens U
22
P cemented with a negative lens U
22
N. The second cemented lens U
23
in the second lens group G
2
is constructed by a negative lens U
23
N cemented with a positive lens U
23
P.
In one preferred embodiment of the present invention, the zoom lens system further includes a third lens group G
3
having positive refractive power located to an image side of the second lens group G
2
. The third lens group G
3
is substantially fixed relative to the image plane when the state of lens group positions varies from the wide-angle end state to the telephoto end state.
In one preferred embodiment of the present invention, the following conditional expressions are satisfied;
0.80<
f
2/|
f
22|<1.70 (1)
1.40<
f
23/|
f
22|<3.50 (2)
where f2 denotes the focal length of the second lens group G
2
, f22 denotes the focal length of the first cemented lens U
22
in the second lens group G
2
, and f23 denotes the focal length of the second cemented lens U
23
in the second lens group G
2
.
In one preferred embodiment of the present invention, the following conditional expressions are satisfied;
n
23
N−n
23
P>
0.13 (3)
&ngr;23
P−&ngr;
23
N>
15 (4)
where n23P denotes the refractive index at d-line (&lgr;=587.6 nm) of the positive lens U
23
P in the second cemented lens U
23
in the second lens group G
2
, n23N denotes the refractive index at d-line of the negative lens U
23
N in the second cemented lens U
23
in the second lens group G
2
, &ngr;23P denotes Abbe number of the positive lens U
23
P in the second cemented lens U
23
in the second lens group G
2
, and &ngr;23N denotes Abbe number of the negative lens U
23
N in the second cemented lens U
23
in the second lens group G
2
.
In one preferred embodiment of the present invention, at least one surface of the first lens U
21
in the second lens group G
2
is an aspherical surface having the shape that the refractive power becomes weak as the height separates from the optical axis.
According to another aspect of the present invention, a zoom lens system includes, in order from an object along an optical axis, a first lens group G
1
having negative refractive power, and a second lens group G
2
having positive refractive power. A fixed stop FS (by the term “fixed stop” in this specification is meant a stop whose aperture diameter is not variable) is arranged between the first lens group G
1
and the second lens group G
2
. A distance between the first lens group G
1
and the second lens group G
2
decreases when the state of lens group positions varies from a wide-angle end state W to a telephoto end state T. When the state of lens group positions varies from the wide-angle end state W to a certain intermediate focal length state M, a distance between the first lens group G
1
and the fixed stop FS decreases as the fixed stop FS is moved with the second lens group G
2
in a body. When the state of lens group positions varies from the certain intermediate focal length state M to the telephoto end state T, a distance between the second lens group G
2
and the fixed stop FS decreases as the fixed stop FS is moved with the first lens group G
1
in a body.
In one preferred embodiment of the present invention, the second lens group G
2
has an aperture stop S and the following conditional expressions are satisfied;
0.80<
fM
/(
fW·fT
)
½
<1.30 (5)
0.25<
D
2
W
/(
D
1
W+D
2
W
)<0.65 (6)
&phgr;
FS·FNOT/fT>
1.40 (7)
&phgr;
FS/&phgr;ST<
1.20 (8)
where fW denotes the focal length of the zoom lens system in the wide-angle end state W, fM denotes the focal length of the certain intermediate focal length state M, fT denotes the focal length of the zoom lens system in the telephoto end state T, D1W denotes the distance between the most image side surface of the first lens group G
1
and the fixed stop FS in the wide-angle end state W, D2W denotes the distance between the fixed stop FS and the most object side surface of the second lens group G
2
in the wide-angle end state W, FNOT denotes f-number of the zoom lens system in the telephoto end state T, &phgr;FS denotes the diameter of the fixed stop FS, and &phgr;ST denotes the maximum diameter of the aperture stop S in the telephoto end state T.
REFERENCES:
patent: 6124984 (2000-09-01), Shibayama et al.
patent: 6304389 (2001-10-01), Shibayama
patent: 6349002 (2002-02-01), Shibayama et al.
patent: 6614599 (2003-09-01), Watanabe
patent: 6643072 (2003-11-01), Mihara
patent: 2002/0012174 (2002-01-01), Horiuchi
patent: 11-23967 (1999-01-01), None
Miles & Stockbridge P.C.
Nikon Corporation
Schwartz Jordan M.
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