Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
1999-03-17
2001-06-19
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S676000, C359S683000
Reexamination Certificate
active
06249389
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to a variable-focal-length lens system, and in particular pertains to a variable-focal-length lens system that is small in size and that has a high zooming ratio.
BACKGROUND OF THE RELATED ART
In recent years, zoom lenses have come into common use in photographic optical systems for use in still cameras, video cameras, and the like; in particular, cameras employing so-called high-zoom lenses wherein zooming ratios are in excess of three are rapidly becoming standard equipment.
Particularly with integral-lens-type cameras, wherein the photographic optical system is integral with the camera main body, importance is placed on portability, and there have accordingly been a variety of proposals pertaining to zoom lenses suitable for applications permitting reduction in size and weight.
Specifically, positive-positive-negative three-group-type lenses (consisting of, in order from the object side, a positive lens group, a positive lens group, and a negative lens group) and positive-negative-positive-negative four-group-type lenses (consisting of, in order from the object side, a positive lens group, a negative lens group, a positive lens group, and a negative lens group) are known as variable-magnification optical systems that are small in size and that are suitable for high zooming ratio.
For example, Japanese Laid-Open Patent Application (Kokai) No. H2 [1990]-73211 and the like are known as examples of positive-positive-negative three-group-type lenses, while Japanese Laid-Open Patent Application (Kokai) No. H2[1990]-207210, Japanese Laid-Open Patent Application (Kokai) No. H6[1994]-265788, and the like are known as examples of positive-negative-positive-negative four-group-type lenses.
Furthermore, the positive-negative-positive-positive-negative five-group-type lens disclosed in Japanese Laid-Open Patent Application (Kokai) No. H7[1995]-27979 is known.
However, there has been the problem that an increase in zooming ratio is accompanied by an increase in focal length, causing the length of the overall lens to become large and adversely affecting portability.
Furthermore, with the positive-positive-negative three-group-type lens, due to the fact that above a zooming ratio of three the lateral magnification of the negative lens group becomes large when in the extreme telephoto state, it is necessary that the positional accuracy of the several lens groups be made extremely precise, with the result that lens performance deteriorates markedly because of the influence of stopping precision. In particular, because of the need to increase the lateral magnification of the negative lens group in order to achieve small size, it has been difficult to simultaneously achieve both small size and high performance.
With the positive-negative-positive-negative four-group-type lens, because of the increased number of movable lens groups the lateral magnification of the negative lens group arranged nearest to the image plane is relaxed i.e., is lessened when in the extreme telephoto state, and, while the zooming ratio might be high and it may be possible to achieve small size and high performance, it has not been possible to achieve adequate wide-angle performance.
While the positive-negative-positive-positive-negative five-group-type lens better permits attainment of high zooming ratio and small size while maintaining high performance as compared with the aforementioned four-group-type lens, because of the large widths of the several lens groups in the direction of the optical axis it has been difficult to achieve improved camera portability.
The object of the present invention is to solve the aforementioned problems and to provide a variable-focal-length lens system that is small in size and that is suitable for applications having a high zooming ratio while maintaining high performance.
SUMMARY OF THE INVENTION
In order to achieve the aforesaid object, the variable-focal-length lens system associated with the present invention possesses, in order from the object side thereof, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power, a fourth lens group having positive refracting power, and a fifth lens group having negative refracting power, an aperture stop being arranged between the aforesaid second lens group and the aforesaid third lens group; all of the lens groups move toward the object side in such fashion as to cause the distance between the aforesaid first lens group and the aforesaid second lens group to increase, the distance between the aforesaid second lens group and the aforesaid third lens group to decrease, the distance between the aforesaid third lens group and the aforesaid fourth lens group to increase, and the distance between the aforesaid fourth lens group and the aforesaid fifth lens group to decrease, when the positional state of the lens changes from the extreme wide-angle state to the extreme telephoto state; the aforesaid second lens group and the aforesaid fourth lens group move in integral fashion during a change in the positional state of the lens; the aforesaid third lens group moves during short-distance focusing; and the following conditional expression (1) is satisfied:
0.05<Dc/{Z·(ft·fw)
½
}<0.1, (1)
where:
Dc=Length along the optical axis from the lens surface at the object-most side of the second lens group to the lens surface at the image-most side of the fourth lens group,
fw=Focal length when in the extreme wide-angle state,
ft=Focal length when in the extreme telephoto state, and
Z=Zooming ratio (=ft/fw).
REFERENCES:
patent: 4978204 (1990-12-01), Ito
patent: 5666229 (1997-09-01), Otaki
patent: 5668667 (1997-09-01), Ohtake
patent: 5696632 (1997-12-01), Ohtake
patent: 5828499 (1998-10-01), Ohtake
patent: 273211 (1990-03-01), None
patent: 2207210 (1990-08-01), None
patent: 6265788 (1994-09-01), None
patent: 727979 (1995-01-01), None
Epps Georgia
Nikon Corporation
Spector David N.
Vorys Sater Seymour and Pease LLP
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