Zoom optical system and camera comprising the same

Details Zoom optical system and camera comprising the same Zoom optical system and camera comprising the same

2002-01-10

2003-05-27

Epps, Georgia (Department: 2873)

Optical: systems and elements

Lens

With variable magnification

C359S690000

Reexamination Certificate

active

06570716

ABSTRACT:

This application claims benefit of Japanese Application No. 2001-3439 filed in Japan on Jan. 11, 2001, the contents of which are incorporated by this reference.
BACKGROUND OF THE INVENTION
The present invention relates generally to a zoom optical system used with image pickup devices, and more particularly to a zoom optical system for use with photographic cameras, especially lens shutter cameras.
Cameras having zoom lenses are now popular for recent lens shutter cameras, and there are growing demands for cameras equipped with a compact phototaking lens having an increased zoom ratio.
Generally, a zoom optical system having a zoom ratio of about 2 to 3 is constructed in the form of a two-group one consisting of, in order from its object side, a lens group having positive refracting power and a lens group having negative refracting power, and a zoom optical system having a zoom ratio of about 3 to 4.5 is set up in the form of a three-group one consisting of, in order from its object side, a lens group having positive refracting power, a lens group having positive refracting power and a lens group having negative refracting power.
In general, two-group zoom arrangements are used especially for lens shutter cameras targeted at low cost and compactness, because of comprising a simple mechanical mechanism with reduced sensitivities of the adjacent lens groups to decentration.
Some two-group zoom lens systems having a zoom ratio of about 3 are generally designed with an angle of view of about 60° at the wide-angle end. On account of growing needs for scenic shots taken at wider-angle ends, which are a reflection of recent going-abroad booms, and for lens shutter cameras with wide-angle zoom lenses at oversea markets, however, there is an increasing demand for two-group zoom lenses having an angle of view of about 70° or greater at the wide-angle ends and having a zoom ratio of about 3.
With zoom lenses having a zoom ratio of about 3 while maintaining an angle of view of about 70° or greater at the wide-angle ends, however, it is difficult to maintain image-formation capability at the telephoto ends.
Lens arrangements so far proposed to overcome such problems are disclosed in JP-A's 11-14903, 2000-28921 and 2000-137163.
However, the lens arrangements set forth in JP-A's 11-14903 and 2000-137163 have a zoom ratio of as low as 2.8 although the angle of view at the wide-angle ends is of the order of 70° or greater. The lens arrangement of JP-A 2000-28921, too, has an zoom ratio of at most 3 although the angle of view at the wide-angle end is 70° or greater.
SUMMARY OF THE INVENTION
In view of such states of the prior art, an object of the invention is provide a zoom optical system having a wider angle of view at the wide-angle end and an increased zoom ratio, especially a compact two-group zoom optical system capable of maintaining satisfactory image-formation capability all over the zooming range, albeit having an angle of view of 70° or greater at the wide-angle end and a zoom ratio of 3 or greater.
According to the first aspect of the invention designed to achieve this object, there is provided a zoom lens optical system having a zoom ratio of 3 or greater and comprising, in order from an object side thereof, a first lens group having positive refracting power and a second lens group having negative refracting power in which, for zooming from a wide-angle end to a telephoto end of the zoom lens optical system, the respective lens groups move toward the object side with a decreasing spacing between the first lens group and the second lens group, wherein:
the first lens group consists of, in order from an object side thereof, a first lens unit (U
1
) having negative refracting power, a second lens unit (U
2
) having positive refracting power and a third lens group (U
3
) having positive refracting power wherein each lens unit consists of a single lens or a cemented lens, and satisfies the following condition:
0.35
<f
G1
/f
12
<1.5  (1)
where f
G1
is the focal length of the first lens group, and f
12
is the focal length of the second lens unit.
According to the second aspect of the invention, there is provided a zoom lens optical system comprising, in order from an object side thereof, a first lens group having positive refracting power and a second lens group having negative refracting power in which, for zooming from a wide-angle end to a telephoto end of the zoom lens optical system, the respective lens groups move toward the object side with a decreasing spacing between the first lens group and the second lens group, wherein:
the first lens group consists of, in order from an object side thereof, a first lens unit (U
1
) having negative refracting power, a second lens unit (U
2
) having positive refracting power and a third lens unit (U
3
) having positive refracting power wherein each lens unit consists of a single lens or a doublet, while the following conditions are satisfied:
0.8
<|f
G1
/f
11
|<3  (2)
0.35
<f
G1
/f
12
<3  (3)
0.8
<f
G1
/f
13
<3  (4)
where f
G1
is the focal length of the first lens group, f
11
is the focal length of the first lens unit, f
12
is the focal length of the second lens unit, and f
13
is the focal length of the third lens unit.
Preferably in the first or second aspect of the invention, the surface, located nearest to the object side, of the first lens unit in the first lens group is concave on the object side.
Preferably in the first or second aspect of the invention, the second lens unit in the first lens group is a doublet consisting of, in order from an object side thereof, a negative meniscus lens convex on an object side thereof and a positive lens.
Preferably, the second lens unit in the first lens group satisfies the following condition:
30<&ngr;
12P
−&ngr;
12N
<50  (5)
where &ngr;
12P
is the Abbe's number of the positive lens in the second lens unit, and &ngr;
12N
is the Abbe's number of the negative lens in the second lens unit.
Preferably in the first, second and subsequent aspects of the invention, the third lens unit in the first lens group comprises at least one aspheric surface that satisfies the following condition:
0<|&Dgr;
A/ST
|<4.5×10
−2
  (6)
where &Dgr;A is the amount of the aspheric surface at a height from an optical system to 0.8 times the radius of an aperture stop, and ST is the radius of the aperture stop at a telephoto end.
According to the third aspect of the invention, there is provided a zoom lens optical system comprising, in order from an object side thereof, a first lens group having positive refracting power and a second lens group having negative refracting power in which, for zooming from a wide-angle end to a telephoto end of the zoom lens optical system, the respective lens groups move toward the object side with a decreasing spacing between the first lens group and the second lens group, wherein:
the first lens group consists of, in order from an object side thereof, a first lens unit (U
1
) having negative refracting power, a second lens unit (U
2
) having positive refracting power and a third lens unit (U
3
) having positive refracting power wherein the first lens unit is a doublet consisting of a negative lens and a positive lens in order from an object side thereof, and the second lens unit is a doublet consisting of a negative lens and a positive lens in order from an object side thereof.
According to the fourth aspect of the invention, there is provided a zoom lens optical system having a zoom ratio of 3 or greater and comprising, in order from an object side thereof, a first lens group having positive refracting power and a second lens group having negative refracting power in which, for zooming from a wide-angle end to a telephoto end of the zoom lens optical system, the respective lens groups move toward the object side with a decreasing spacing between the first lens group and the second lens group, wherein:
the first lens group consist

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