Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2003-06-26
2004-12-28
Spector, David N. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S689000, C359S684000
Reexamination Certificate
active
06836375
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens system suitable for a photographing optical system, such as a digital still camera or a video camera, using a solid-state imaging device, such as a CCD sensor or a CMOS sensor.
2. Description of the Related Art
In recent years, along with the popularization of compact and sophisticated video cameras, digital still cameras, or electronic still cameras using solid-state imaging devices, such as CCD sensors or CMOS sensors, there is a growing requirement for high optical performance and reduced size of the optical systems used therein.
Generally, as a zoom lens employed in a photographing optical system for a still camera, which is used for capturing still images using the CCD sensor, an optical system including a lens whose entire length is extremely short, whose field angle of the lens is wide according to the nature of the still image, and whose optical performance is higher than a zoom lens employed in a photographing optical system for a video camera for photographing moving images has been increasingly required.
Japanese Patent Publication No. 7-52256 (corresponding to U.S. Pat. No. 4,733,952) proposes a zoom lens including three lens units having negative, positive, and positive refractive powers, respectively, in which the distance between the second lens unit and the third lens unit increases during zooming from the wide-angle end to the telephoto end.
U.S. Pat. No. 5,434,710 discloses a zoom lens including three lens units having negative, positive, and positive refractive powers, respectively, in which the distance between the second lens unit and the third lens unit decreases during zooming from the wide-angle end to the telephoto end.
U.S. Pat. No. 4,465,343, Japanese Patent Laid-Open NO. 11-84243 (corresponding to U.S. Pat. No. 6,191,896), Japanese Patent Laid-Open No. 2000-284177 (corresponding to U.S. Pat. No. 6,351,337), Japanese Patent Laid-Open No. 2000-137164, and Japanese Patent Laid-Open No. 2000-147381 (corresponding to U.S. Pat. No. 6,243,213) propose zoom lenses including three lens units having negative, positive and positive refractive powers, respectively, in which the distance between the first lens unit and the second lens unit, and the distance between the second lens unit and the third lens unit vary during zooming.
Japanese Patent Laid-Open No. 2000-9997 (corresponding to U.S. Pat. No. 6,124,987) proposes a zoom lens including two lens units having negative and positive refractive powers, respectively, in which the second lens unit includes a first subunit
2
a
having positive refractive power and a second subunit
2
b
having positive refractive power, in which the second subunit
2
b
carries out a focusing operation.
Japanese Patent Laid-Open No. 2000-009999 (corresponding to U.S. Pat. No. 6,172,818), Japanese Patent Laid-Open No. 10-213745, Japanese Patent Laid-Open No. 9-258103 (corresponding to U.S. Pat. No. 5,872,660), and Japanese Patent Laid-Open No. 11-52237 (corresponding to U.S. Pat. No. 6,081,389) propose zoom lenses including three lens units having negative, positive, and positive refractive powers, respectively, in which the second lens unit includes a positive lens and a negative lens.
Although the three-unit zoom lenses disposed in the order of negative, positive, and positive refractive power sequentially from the object side, which are disclosed in the related art, are preferable as zoom lenses used for a wide-angle of view, variations in aberrations during zooming tend to increase as the angle of view increases.
SUMMARY OF THE INVENTION
In view of the zoom lenses disclosed in the related art, an object of the present invention is to provide a zoom lens having a superior optical performance without increasing the number of lenses included therein.
In order to achieve the above-described object, a zoom lens system according to an aspect of the invention includes, in order from the front (on the object side if it is a camera) to the rear (the image side if it is a camera), a first lens unit having negative optical power (reciprocal of focal length), an aperture stop, a second lens unit having positive optical power, and a third lens unit of positive optical power. The distance between the first lens unit and the second lens unit varies during zooming. The second lens unit consists of, in order from the front to the rear, a positive lens element and a negative lens element disposed at a distance therefrom. The distances between the second lens unit and the third lens unit at a short focal length end (so-called wide-angle end) and at a long focal length end (so-called telephoto end) are set to suitable values.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments (with reference to the attached drawings).
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