Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2001-05-09
2003-07-01
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S685000, C359S687000
Reexamination Certificate
active
06587280
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens and an optical device using the zoom lens, which is particularly suitable for use in optical equipment such as electronic cameras, including a video camera and a digital still camera, and film cameras. Also, the present invention relates to a zoom lens, which has a short overall length and a large aperture ratio with the F-number being about 1.6 at the wide-angle end while it has a zoom magnification ratio as high as on the order of 10, and an optical device using the zoom lens.
2. Description of the Related Art
Hitherto, a zoom lens having a relatively small overall lens system and a relatively high zoom magnification ratio has been proposed in, e.g., Japanese Patent Laid-Open Nos. 56-114920 and 58-160913 (U.S. Pat. No. 4,720,180). This zoom lens comprises four lens units, i.e., a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, and a fourth lens unit having positive refractive power, which are arranged in this order from the object side. The first, second and fourth lens units are moved for zooming. With such an arrangement, a relatively high zoom magnification ratio is provided while the overall lens system is of a relatively small size.
Japanese Patent Laid-Open Nos. 62-24213 (U.S. Pat. No. 4,859,042) and 62-247316 propose a zoom lens similarly comprising four lens units, i.e., a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, and a fourth lens unit having positive refractive power, which are arranged in this order from the object side. In this zoom lens, however, the second lens unit is moved for zooming and the fourth lens unit is moved to compensate for a shift of an image plane (field shift) upon zooming. Further, the fourth lens unit also serves for focusing.
Also, Japanese Patent Laid-Open No. 4-14007 (U.S. Pat. No. 5,134,524) discloses a zoom lens comprising a first lens unit having positive refractive power, a second lens unit having negative refractive power, an aperture stop, a third lens unit having positive refractive power, and a fourth lens unit having positive refractive power, which are arranged in this order from the object side. For zooming from the wide-angle end to the telephoto end, the first lens unit is moved toward the object side and the second lens unit is moved toward the image (plane) side. The fourth lens unit is moved for zooming and focusing. Further, the aperture stop is moved toward the image side for zooming from the medium focal length to the telephoto end.
Japanese Patent Laid-open Nos. 58-129404 and 61-258217 (U.S. Pat. No. 4,776,680) disclose a zoom lens comprising five lens units, i.e., a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, a fourth lens unit having positive refractive power, and a fifth lens unit having negative refractive power, which are arranged in this order from the object side. The fifth lens unit or a plurality of lens units including the fifth lens unit is moved for focusing.
Japanese Patent Laid-Open No. 4-301811 discloses a zoom lens comprising five lens units, i.e., a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, a fourth lens unit having positive refractive power, and a fifth lens unit having negative refractive power, which are arranged in this order from the object side, with an aperture stop situated between the second and third lens units. For zooming from the wide-angle angle end to the telephoto end, the first lens unit is moved toward the object side, the second lens unit is moved toward the image side, and the aperture stop is kept fixed. The fourth lens unit is moved not only to compensate for shift of an image plane upon zooming, but also to serve for focusing.
U.S. Reissue Pat. No. 32,923 discloses a zoom lens comprising a first positive lens unit, a second negative lens unit, an aperture stop, a third positive lens unit, and a fourth positive lens unit, which are arranged in this order from the object side. For zooming, the first and fourth lens units are moved in the same direction while the stop is kept fixed.
Japanese Patent Laid-Open Nos. 4-14006 (U.S. Pat. No. 5,134,524) and 4-358108 (U.S. Pat. No. 5,341,243) disclose a zoom lens comprising a first lens unit having positive refractive power, a second lens unit having negative refractive power, an aperture stop, a third lens unit having positive refractive power, and a fourth lens unit having positive refractive power, which are arranged in this order from the object side. For zooming from the wide-angle end to the telephoto end, the first lens unit is moved toward the object side and the second lens unit is moved toward the image side. The fourth lens unit is moved for zooming and focusing, while the aperture stop is always kept fixed during the zooming.
Japanese Patent Laid-Open No. 11-242160 discloses a zoom lens comprising a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, and a fourth lens unit having positive refractive power, which are arranged in this order from the object side. For zooming from the wide-angle end to the telephoto end, the first and fourth lens units are moved toward the object side and the second lens unit is moved toward the image side. The third lens unit and an aperture stop are always kept fixed during the zooming.
Moreover, Japanese Patent Laid-Open No. 5-143178 discloses a zoom lens comprising a first lens unit having positive refractive power, which is kept fixed during zooming, a second lens unit having negative refractive power, an aperture stop, a third lens unit having positive refractive power, and a fourth lens unit constituted by a single lens having positive refractive power, which are arranged in this order from the object side. The aperture stop is moved for zooming.
Recently, there has been a demand for a zoom lens used in optical equipment, such as a single-lens reflex camera and a video camera, which has a zoom magnification ratio as high as on the order of 10 and also has a small overall lens system.
In general, to obtain a zoom lens having a high zoom magnification ratio, a short overall lens system and high optical performance over a full zooming range, a lens arrangement, a refractive power of each lens unit, etc. must be properly set.
Unless, for example, moving conditions of each lens unit in zooming, a refractive power of each lens unit, a lens arrangement of each zooming lens unit, a selection of one or more lens units for focusing and a lens arrangement of each selected lens unit, an optical action of an aperture stop, etc. are properly set, aberrations that occur upon zooming and focusing increase to such an extent that it is difficult to obtain a high-quality image while realizing a high zoom magnification ratio.
In a zoom lens, it is a generally known principle that intensifying refractive power of each lens unit is effective to increase a zoom magnification ratio and shorten the overall lens system, because the amount by which each lens unit must be moved for obtaining a predetermined zoom magnification ratio is reduced correspondingly.
Simply intensifying refractive power of each lens unit, however, raises a problem that variations of aberrations upon zooming are increased and it is difficult to obtain high optical performance over a full zooming range.
Meanwhile, by employing rear focusing in a zoom lens, advantageous features result, for example, in that the size of an overall lens system is reduced, more rapid focusing is realized, and macro (close-up) shooting is facilitated.
However, variations of aberrations upon zooming are increased, which makes it very d
Canon Kabushiki Kaisha
Epps Georgia
Fitzpatrick ,Cella, Harper & Scinto
Spector David N.
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