Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
1999-05-25
2001-01-23
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S684000
Reexamination Certificate
active
06178050
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens system in which a back focal distance can be short.
2. Description of the Related Art
In a zoom lens system in which a back focal distance can be short (e.g., a zoom lens system for a compact camera), there is no need to provide a longer back focal distance unlike a zoom lens system for a single lens reflex (SLR) camera, which requires a space for providing a mirror behind the photographing lens. Accordingly, a compact camera generally employs a telephoto type lens system in which positive and negative lens groups are provided in this order from the object side while a retrofocus type lens system, which includes negative and positive lens groups in this order from the object side, is generally employed in a SLR camera.
A telephoto two-lens group zoom lens system, which has a positive front lens group and a negative rear lens group, is simple, easy to adjust upon assembly, can reduce the number of lens elements, and is beneficial from the viewpoint of cost. However, in order to decrease the F-number at the long focal length extremity and to achieve high optical performance, aberration correction of the front lens group becomes the utmost importance, and the number of lens elements of the positive front lens group increases. Accordingly, the front lens group becomes heavy, so that the focusing mechanism has to bear a load.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a two-lens group zoom lens system wherein even if the front lens group includes an increased number of lens elements in order to provide improved optical performance, a load otherwise exerted to the focusing mechanism can substantially be removed.
In order to achieve the above-mentioned object, there is provided a zoom lens system including a positive first lens group and a negative second lens group in this order from the object side, wherein the distance between the first and second lens groups is varied upon zooming. A middle or rear portion of the positive first lens group is formed as a focusing lens group so that the focusing lens group can be moved along the optical axis without changing the distance between the most-object side lens surface of the first positive lens group and the image plane when focusing is performed.
The zoom lens system preferably satisfies the following condition:
0.5<f
1G
/f
F
<1.2 (1)
wherein
f
1G
designates the focal length of the positive first lens group; and
f
F
designates the focal length of the focusing lens group in the positive first lens group.
In addition to, or regardless of condition (1), the zoom lens system preferably satisfies the following condition:
0.1<&Sgr;d
F
/&Sgr;d
1G
<0.8 (2)
wherein
&Sgr;d
F
designates the distance between the most object-side lens surface and the most image-side lens surface of the focusing lens group in the positive first lens group; and
&Sgr;d
1G
designates the distance between the most object-side lens surface and the most image-side lens surface of the positive first lens group.
The present disclosure relates to subject matter contained in Japanese Patent Application No.10-144513 (filed on May 26, 1998) which is expressly incorporated herein by reference in its entirety.
REFERENCES:
patent: 4836660 (1989-06-01), Ito
patent: 4906077 (1990-03-01), Ito
patent: 4984877 (1991-01-01), Ito
patent: 5164859 (1992-11-01), Ito
patent: 5280390 (1994-01-01), Ito
patent: 5570235 (1996-10-01), Yoneyama
patent: 5751498 (1998-05-01), Ito
patent: 5910860 (1999-06-01), Ozaki et al.
patent: 6002528 (1999-12-01), Tomita
patent: 6016228 (2000-01-01), Uzawa
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Sugarman Scott J.
LandOfFree
Zoom lens system 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 system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Zoom lens system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2472610