Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2002-01-22
2004-04-13
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S682000
Reexamination Certificate
active
06721107
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a three-lens-group zoom lens system for a compact camera, and in particular relates to making the angle-of-view at the short focal length extremity larger.
2. Description of the Prior Art
A zoom lens system of a compact camera does not require a long back focal distance unlike a zoom lens system of a single lens reflex camera in which a space for a quick-return mirror is required behind the photographing lens system. Accordingly, a compact camera has employed a telephoto lens system including a positive powered (herein after, positive) lens group and a negative powered (hereinafter, negative) lens group, in this order from the object. On the other hand, a single lens reflex camera has employed a retrofocus lens system including a negative lens group and a positive lens group, in this order from the object.
In a conventional telephoto zoom lens system of a compact camera, the half angle-of-view at the short focal length extremity is at most about 30°. Moreover, a three-lens-group zoom lens system which can attain the half angle-of-view of more than 35° at the short focal length extremity has not been known.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a miniaturized three-lens-group zoom lens system for a compact camera in which the half angle-of-view of more than 35° at the short focal length extremity can be attained.
In order to achieve the above-mentioned object, there is provided a zoom lens system including a negative first lens group, a positive second lens group, and a negative third lens group, in this order from the object. Zooming is performed by moving the first through third lens groups in the optical axis direction. The negative first lens group is constituted by a negative single lens element having a concave surface facing toward the object, and satisfies the following condition:
−1
<r
1
/
fW
<−0.3 (1)
wherein
r
1
designates the radius of curvature of the object-side concave surface of said negative single lens element; and
fW designates the focal length of the entire zoom lens system at the short focal length extremity.
The negative single lens element having the concave surface facing toward the object can be constituted by a negative meniscus lens element.
The zoom lens system of the present invention preferably satisfies the following condition:
50<&ngr;d (2)
wherein
&ngr;d designates the Abbe number of the negative single lens element.
The zoom lens system of the present invention can satisfy the following condition:
1.7<nd (3)
wherein
nd designates the refractive index of the d-line of the negative single lens element.
The zoom lens system of the present invention preferably satisfies the following condition:
−5
<fT/f
1
G
<−3 (4)
wherein
fT designates the focal length of the entire zoom lens system at the long focal length extremity; and
f1G designates the focal length of the negative single lens element.
The zoom lens system of the present invention preferably satisfies the following condition:
0.05<(
d
12
W−d
12
T
)/
fW
<0.15 (5)
wherein
d
12
W designates the distance between the negative single lens element and the second lens group at the short focal length extremity; and
d
12
T designates the distance between the negative single lens element and the second lens group at the long focal length extremity.
The zoom lens system of the present invention can satisfy the following condition:
0.6
<y/fw
<0.9 (6)
wherein
y designates the diagonal image height on a film surface.
The zoom lens system of the present invention can satisfy the following condition:
3.5
<fT/fW
(7)
wherein
fT designates the focal length of the entire zoom lens system at the long focal length extremity; and
fW designates the focal length of the entire zoom lens system at the short focal length extremity.
The positive second lens group includes a lens element having at least one aspherical surface, and can satisfy the following condition:
−30<&Dgr;IASP<−10 (8)
wherein
&Dgr;IASP designates the amount of change of the spherical aberration coefficient due to the aspherical surface under the condition that the focal length at the short focal length extremity is converted to 1.0.
The negative third lens group includes a lens element having at least one aspherical surface, and can satisfy the following condition:
0<&Dgr;VASP<0.4 (9)
wherein
&Dgr;VASP designates the amount of change of the distortion coefficient due to the aspherical surface under the condition that the focal length at the short focal length extremity is converted to 1.0.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2001-015740 (filed on Jan. 24, 2001) which is expressly incorporated herein in its entirety.
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Greenblum & Bernstein P.L.C.
PENTAX Corporation
Ralzen Deborah A.
Sugarman Scott J.
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