Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
1999-08-30
2001-06-05
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S689000
Reexamination Certificate
active
06243213
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a zoom lens and a camera having the zoom lens, and in particular, to a zoom lens having a magnification ratio of about 2.5 to 4 suitable for an electronic still camera or a video camera employing a solid state image sensor such as CCD.
In recent years, there has been development of rapid strides of a software handling image data, together with technical advancement and spread of a personal computer, and there is a growing demand for an electronic still camera which is used to input images in a personal computer.
As a zoom lens for a solid state image sensor, there has been disclosed a zoom lens of a three-group structure type or of a four-group structure type, wherein a zoom lens for a video camera tends to be of a high magnification ratio, and a zoom lens of a four-group structure type is widely used for the video camera, while as a zoom lens for an electronic still camera, those meeting high resolution and high image quality are demanded, and many of them have a magnification ratio, namely the ratio of a focal length at the telephoto end position to that at the wide angle end position, of about 3, and a zoom lens of a three-group structure type has been disclosed as one having the magnification ratio of about 3.
A zoom lens for a solid state image sensor having a magnification ratio-of about 3has been disclosed in each of Japanese TOKKAIHEI Nos. 10-133115, 10-39214 and 10-104518.
However, in these conventional examples, there have been problems that distortion at the wide angle end position is −5% or more (less?), or a field angle at the wide angle end position is small although distortion is small, and a total length of a lens is great.
SUMMARY OF THE INVENTION
The invention has been achieved in view of these problems, and an object of the invention is to provide a zoom lens having a small total length and a magnification ratio of 2.5 or more wherein distortion at the wide angle end position and lateral chromatic aberration are satisfactorily corrected.
The objective mentioned above can be attained by either one of the following structures.
Structure 1: A zoom lens having a variable power ratio of not less than 2.5 times which has a first lens group having a negative focal length, an aperture-stop, a second lens group having a positive focal length, and a third lens group having a positive focal length, in this order from an object, wherein when a magnification of the zoom lens is varied from the wide angle position to the telephoto end position, all of the first, second and third lens groups are moved in the direction of the optical axis of the zoom lens, and the first lens group has a first lens representing a positive lens whose convex surface faces an object, a second lens representing a negative meniscus lens whose convex surface faces an object, a third lens representing a negative lens, and a fourth lens representing a positive lens, in this order from an object.
Structure 2: The zoom lens according to Structure 1, wherein when a magnification of the zoom lens is varied from the wide angle position to the telephoto end position, the first lens group and the second lens group are moved so that a distance between the first lens group and the second lens group may be reduced.
Structure 3: The zoom lens according to Structure 1, wherein the following expressions are satisfied,
&ngr;1>50 (1)
&ngr;4>30 (2)
where &ngr;1 and &ngr;4 represent Abbe's numbers respectively for the first lens and the fourth lens both in the first lens group.
Structure 4: The zoom lens according to Structure 1, wherein the following expression is satisfied,
1.3<f1/fL3 <2.0 (3)
where f1 represents a focal length of the first lens group, and fL3 represents a focal length of the third lens in the first lens group.
Structure 5: The zoom lens according to Structure 1, wherein the second lens group has two negative lenses and two positive lenses, and the two positive lenses represent a lens closest to an object and a lens closest to an image both in the second lens group, and one of the two negative lenses is cemented to a positive lens.
Structure 6: The zoom lens according to Structure 1, wherein the following expression is satisfied,
1.15<fT/|f1|<1.40 (4)
where f1 represents a focal length of the first lens group, and fT represent a focal length of the zoom lens total system at the telephoto end position.
Structure 7: A digital still camera having therein the zoom lens of the Structure 1.
Structure 8: A video camera having therein the zoom lens of the Structure 1.
Structure 9: A zoom lens having a variable power ratio of not less than 2.5 times which has a first lens group having a negative focal length, an aperture-stop, a second lens group having a positive focal length, and a third lens group having a positive focal length, in this order from an object, wherein when a magnification of the zoom lens is varied from the wide angle position to the telephoto end position, all of the first, second and third lens groups are moved in the direction of the optical axis of the zoom lens, the second lens group has two negative lenses and two positive lenses, the two positive lenses represent a lens closest to an object and a lens closest to an image both in the second lens group, one of the two negative lenses is cemented to a positive lens, and following expression is satisfied,
1.15<fT/|f1|<1.40
where fT represents a focal length of the zoom lens total system at the telephoto end position, and f1 represent a focal length of the first lens group.
Structure 10: The zoom lens according to Structure 9, wherein when a magnification of the zoom lens is varied from the wide angle position to the telephoto end position, the first lens group and the second lens group are moved so that a distance between the first lens group and the second lens group may be reduced.
Structure 11: The zoom lens according to Structure 9, wherein the following expressions are satisfied.
&ngr;1>50
&ngr;4>30
Structure 12: A digital still camera having therein the zoom lens of the Structure 9.
Structure 13: A video camera having therein the zoom lens of the Structure 9.
Structure 14: A zoom lens which has a first lens group having a negative focal length, an aperture-stop, a second lens group having a positive focal length, and a third lens group having a positive focal length, in this order from an object, wherein when a magnification of the zoom lens is varied from the wide angle position to the telephoto end position, all of the first, second and third lens groups are moved in the direction of the optical axis of the zoom lens, in which focusing is carried out by moving the third lens group in the optical axis direction, and the following conditional expression is satisfied,
0<(D
23T
−D
23W
)/(D
12W
−D
12T
)<0.22
where D
12W
represents a distance between the first lens group and the second lens group at the wide angle end position, D
23W
represents a distance between the second lens group and the third lens group at the wide angle end position, D
12T
represents a distance between the first lens group and the second lens group at the telephoto end position, D
23T
represents a distance between the second lens group and the third lens group at the telephoto end position.
Structure 15: The zoom lens according to Structure 14, wherein when a magnification of the zoom lens is varied from the wide angle position to the telephoto end position, the first lens group and the second lens group are moved so that a distance between the first lens group and the second lens group may be reduced.
Structure 16: The zoom lens according to Structure 14, wherein the following expression is satisfied,
1.15<fT/|f1|<1.40
where f1 represents a focal length of the first lens group, and fT represents a focal length of the total system of the zoom lens at the telephoto end position.
Structure 17: The zoom lens according to Structure 14, whe
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Konica Corporation
Sugarman Scott J.
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