Step zoom lens

Details Step zoom lens Step zoom lens

1999-06-24

2001-07-31

Epps, Georgia (Department: 2873)

Optical: systems and elements

Lens

With variable magnification

C359S682000, C359S691000

Reexamination Certificate

active

06268964

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens for a digital camera, a video camera or a compact camera.
2. Description of the Related Art
In general, in a zoom lens, the focal length can be continuously varied by moving movable variable power lens groups (a plurality of lens groups which move along the optical axis upon zooming) in a stepless fashion. In a single lens reflex camera in which an object image formed by a photographing lens system is viewed through a view finder, it is preferable to be able to stop the variable power lens groups at a desired position. In a single lens reflex camera in which the focal length of the photographing lens is detected electrically and is used to control predetermined operations, it is possible to mechanically stop the variable power lens groups at a desired focal length position so as to prevent the object image from appearing unnatural due to the discontinuous zooming operation. Furthermore, the focal lengths can be detected stepwise at practical intervals, and can be used to control a predetermined operation. Namely, the function of stopping the variable power lens groups itself at a desired position is a different matter not to be confused with the stepwise detection of the focal length.
In a digital camera, video camera or compact camera, in which an image other than an image formed by a photographing optical system is viewed through a finder optical system, the stepless stoppage of the variable power lens groups in the finder optical system has less merit. Therefore, the variable power lens groups are stopped stepwise and the focal length is detected stepwise.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a small zoom lens (hereinafter termed as a step zoom lens) having a specific fundamental zooming path which is carried out in a stepwise (discontinuous) fashion, and wherein a sufficient space can be provided around a diaphragm in the optical axis direction (i.e., in front or behind the diaphragm).
According to the present invention, there is provided a step zoom lens comprising a first movable lens group having negative refracting power, a diaphragm which is immovable during zooming, and a second movable lens group having positive refracting power, in this order from the object side; wherein: a fundamental zooming path along which the first lens group is moved to vary a focal length without causing an image shift is defined so that the distance of the first lens group from the diaphragm is reduced and is thereafter increased, and a fundamental zooming path along which the second lens group is moved is defined so that the distance of the second lens group from the diaphragm is linearly varied, upon zooming from a wide angle extremity to a telephoto extremity; and the first and second lens groups are stopped stepwise on the respective fundamental zooming paths to constitute a step zoom, and wherein the discrete stop positions of the first lens groups are determined to be different from a focal length position at which the distance between the first lens group and the diaphragm on the the fundamental zooming path thereof is at a minimum or at a near minimum.
Preferably, at least two discrete stop positions of the first lens group are located on opposite sides of an apex of the fundamental zooming path thereof, wherein the distance between the first lens group and the diaphragm is at a minimum.
Preferably, the stop positions of the first lens group located on opposite sides of the apex are identical.
Alternatively, a third lens group can be further provided which is immovable during the zooming operation, the third lens group being located between the second lens group and the image surface.
Preferably, the discrete stop positions are set so that each displacement of the second lens group upon zooming is identical.
Preferably, the discrete stop positions are set so that the displacement of the second lens group upon zooming is an integer which is a multiple of the minimum displacement of the second lens group.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 10-181031 (filed on Jun. 26, 1998) which is expressly incorporated herein by reference in its entirety.


REFERENCES:
patent: 4963005 (1990-10-01), Tsjui

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