Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2000-03-08
2001-05-29
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S676000, C359S687000
Reexamination Certificate
active
06239920
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a zoom lens system, and more particularly, to a zoom lens system suitable for the photo-taking optical system of a digital camera or lens shutter camera.
2. Background of the Invention
Various types of zoom lens systems for use in a digital camera or lens shutter camera have conventionally been proposed that comprise, from the object side, a first lens unit having positive optical power, a second lens unit having negative optical power, a third lens unit having positive optical power and a fourth lens unit having positive optical power.
However, in these conventional zoom lens systems, the focal length in the shortest focal length condition is around 40 mm if converted into a camera using 35 mm film. These zoom lens systems are therefore unsatisfactory for a user desiring a shorter focal length.
In addition, the need has increased in recent years for zoom lens systems for digital and lens shutter cameras that permit photo-taking of an object at close distance, and among the zoom lens systems having the optical power arrangement described above, a zoom lens system capable of macro-photography has been proposed (Japanese Published Patent Application 5-76009).
However, the zoom lens system disclosed in said patent application has a construction in which the lens units move along the optical axis in a complex manner for the purposes of photo-taking of an object at close distance (hereinafter macro-focusing) and changing the magnification. Therefore, it is necessary to manufacture the lens barrel with high precision. If the lens barrel is not manufactured with sufficiently high precision, the lens units would become decentered while moving for macro-focusing or zooming, which would lead to a marked deterioration of the image.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a zoom lens system that has a shorter focal length in the shortest focal length condition than conventionally known zoom lens systems used in a digital camera or lens shutter camera, and that offers good aberration correction.
Another object of the preset invention is to provide a zoom lens system capable of performing macro-photography that has a simple construction and may be manufactured at low cost.
In order to attain these objects, the zoom lens system of the present invention has the following components arranged in the order shown from the object side:
a first lens unit that has positive optical power and is fixed during zooming;
a second lens unit that has negative optical power and moves along the optical axis during zooming;
a third lens unit that has positive optical power; and
a fourth lens unit that has positive optical power,
wherein said zoom lens system satisfies the following condition:
1.5
<
&LeftBracketingBar;
f
1
,
2
f
w
&RightBracketingBar;
<
1.85
where
f
1,2
: combined focal length of the first and second lens units in the shortest focal length condition;
f
w
: focal length of the entire zoom lens system in the shortest focal length condition.
Another zoom lens system of the present invention has the following components arranged in the order shown from the object side:
a first lens unit that has positive optical power and is fixed during zooming;
a second lens unit that has negative optical power and moves along the optical axis during zooming;
a third lens unit that has positive optical power and is fixed during zooming; and
a fourth lens unit that has positive optical power and moves along the optical axis during zooming,
wherein said second lens unit is moved along the optical axis during macro-focusing.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention.
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patent: 4818083 (1989-04-01), Mihara
patent: 4840468 (1989-06-01), Tanaka
patent: 4842385 (1989-06-01), Tanaka
patent: 4859042 (1989-08-01), Tanaka
patent: 4952039 (1990-08-01), Ito
patent: 5100223 (1992-03-01), Ono et al.
patent: 5530590 (1996-06-01), Saito
patent: 5546231 (1996-08-01), Sato
patent: 5585966 (1996-12-01), Suzuki
patent: 5734510 (1998-03-01), Ito
patent: 5760971 (1998-06-01), Inadome
patent: 5978149 (1999-11-01), Hashimura et al.
patent: 5-76009 (1993-03-01), None
Matsumoto Hiroyuki
Miyata Akio
Okubo Osamu
Epps Georgia
Minolta Co. , Ltd.
Schwartz Jordan M.
Sidley & Austin
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