Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2000-02-07
2001-12-04
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S683000
Reexamination Certificate
active
06327100
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a zoom lens, and more particularly to a zoom lens system having a low telephoto ratio.
So far, two-group zoom lens systems have been used primarily for zoom lenses having a relatively low magnification, and three-group zoom lens systems have been adopted mainly for zoom lenses having a higher magnification. These zoom lens systems are operated in various zooming modes; however, this results in an increase in the number of lens groups involved. To reduce the number of lens groups and lens elements, the aperture ratios of the systems at their telephoto ends are reduced depending on their operating modes, while full use is made of aspherical surfaces.
For zoom lenses used on compact cameras, there is a zoom lens system disclosed in JP-B 8-3580 published under the name of the applicant. The zoom lens system set forth in JP-B 8-3580 comprises, in order from its object side, a first lens group having positive refracting power, a second lens group having positive refracting power and a third lens group having negative refractive power. For zooming from the wide-angle end to the telephoto end of the zoom lens system, each lens group moves toward the object side. This zoom lens system becomes shortest at the wide-angle end and longest at the telephoto end.
This zoom lens system is characterized in that the amount of zooming movement of the third lens group is larger than those of the rest, thereby achieving a higher zoom ratio. The publication teaches that focusing is effected by the movement of the second lens group, thereby achieving the most stable image-formation capabilities.
For four-group zoom lenses used on compact cameras, on the other hand, there is a zoom lens system disclosed in JP-B 8-30783 published under the name of the applicant, which comprises, in order from its object side, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power and a fourth lens group having negative refracting power. From the wide-angle end to the telephoto end of the zoom lens system, each lens group moves toward the object side.
This zoom lens system is characterized in that the zoom ratio is allocated to each lens group by the movement of each lens group, thereby achieving a high magnification. For zooming from the wide-angle end to the telephoto end, the second lens group is allowed to move toward the object side, so that size reductions are achievable at the wide-angle end.
Some proposals have been made to divide each lens group into subgroups for zooming movement (JP-A's 7-27979, 8-29688, 8-110471 and 9-159918).
To reduce the size of lens systems as mentioned above, many proposals have so far been made of taking full advantage of aspherical surfaces having great ability to correct for aberrations, thereby reducing the number of lenses forming one lens group. Many proposals have also been made of using a radial type gradient index lenses.
Most of actual zoom lens systems for compact cameras have a mechanism for accommodating them in camera bodies irrespective of their types. To this end, a lens collapsible mount mechanism is provided in a space defined in a lens position at the wide-angle end where the zoom lens system becomes shortest to move the zoom lens system therein. It is thus possible to reduce the size of the camera during lens collapsing.
In taking actual shots, however, the zoom lens system must be used in the form of the original optical system, and so a lens mount (for holding the lens system) projects from the camera body. Especially in the case of a zoom lens system having a high zoom ratio, the amount of movement of lenses in association with zooming becomes large at the telephoto end. This means that the overall length of the lens system, i.e., the lens mount increases largely. For this reason, the center of gravity shifts more largely at the telephoto end than during lens collapsing or at the wide-angle end, making the balance of the camera worse and rendering the camera difficult to handle.
SUMMARY OF THE INVENTION
In view of such situations as mentioned above, an object of the present invention is to provide a zoom lens system which, albeit having a high zoom ratio, has its overall length reduced during storage and at its wide-angle end and at its telephoto end as well, and has well-corrected aberrations.
According to the first aspect of the invention, the aforesaid object is achieved by the provision of a zoom lens system comprising a front lens group located nearest to an object side of said zoom lens system, a rear lens group located nearest to an image side of said zoom lens system and at least one lens group located between said front lens group and said rear lens group, wherein:
said front lens group has positive or negative refracting power, said rear lens group has negative refracting power and a separation between adjacent lens groups varies for zooming from a wide-angle end to a telephoto end of said zoom lens system, and conditions (I), (II) and (III) are satisfied:
0.02
<|f
L
|/f
T
<0.3 (I)
0.1<&Dgr;X
LT
/f
T
<0.7 (II)
1.5
<&bgr;
LT
/&bgr;
LW
<6 (III)
where f
L
is a focal length of said rear lens group, f
T
is the focal length of said zoom lens system at said telephoto end, &Dgr;X
LT
is the amount, on the basis of said wide-angle end, of zooming movement of said rear lens group to said telephoto end, &bgr;
LT
is the transverse magnification of said rear lens group at said telephoto end, and &bgr;
LW
is the transverse magnification of said rear lens group at said wide-angle end.
According to the second aspect of the present invention, there is provided a zoom lens system comprising, in order from an object side of said zoom lens system, a first lens group having positive refracting power, a second lens group having positive refracting power and a third lens group having negative refracting power, wherein:
each of said respective lens groups moves to said object side upon zooming from a wide-angle end to a telephoto end of said zoom lens system while a separation between said first lens group and said second lens group becomes wide and a separation between said second lens group and said third lens group becomes narrow, and conditions (1), (2) and (3) are satisfied:
0.03
<|f
3
|/f
T
<0.25 (1)
0.2
<&Dgr;X
3T
/f
T
<0.44 (2)
1.5<&bgr;
3T
/&bgr;
3W
<6.0 (3)
where f
3
is the focal length of said third lens group, f
T
is the focal length of said zoom lens system at said telephoto end, &Dgr;X
3T
is the amount, on the basis of said wide-angle end, of zooming movement of said third lens group to said telephoto end, &bgr;
3T
is the transverse magnification of said third lens group at said telephoto end, and &bgr;
3W
is the transverse magnification of said third lens group at said wide-angle end.
According to the third aspect of the present invention, there is provided a zoom lens system comprising, in order from an object side of said zoom lens system, a first lens group having positive refracting power, a second lens group having positive refracting power, a third lens group having positive refracting power and a fourth lens group having negative refracting power, wherein:
each of said lens groups moves to said object side upon zooming from a wide-angle end to a telephoto end of said zoom lens system while a separation between said first lens group and said second lens group becomes wide and a separation between said third lens group and said fourth lens group becomes narrow, and conditions (4), (5) and (6) are satisfied:
0.02
<|f
4
|/f
T
<0.3 (4)
0.1
<&Dgr;X
4T
/f
T
<0.5 (5)
1.5<&bgr;
4T
/&bgr;
4W
<6.0 (6)
where f
4
is the focal length of said fourth lens group, f
T
is the focal length of said zoom lens system at said telephoto end, &Dgr;X
4T
is the amount, on the basis of said wide-angle en
Olympus Optical Co,. Ltd.
Pillsbury & Winthrop LLP
Sugarman Scott J.
LandOfFree
Zoom lens does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Zoom lens, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Zoom lens will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2575449