Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2006-01-24
2006-01-24
Lester, Evelyn A. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S761000, C359S680000, C359S682000, C359S683000, C359S752000
Reexamination Certificate
active
06989939
ABSTRACT:
Disclosed is a variable-power optical system, including, sequentially from a front side to a rear side, a negative-refractive-power first lens unit that does not move for zooming, a positive-refractive-power second lens unit, a negative-refractive-power third lens unit, a fourth lens unit, a negative-refractive-power fifth lens unit, and a positive-refractive-power sixth lens unit that does not move for zooming, in which the following conditional expression is satisfied:in-line-formulae description="In-line Formulae" end="lead"?1.7<bf/(|f1|·fw)1/2<2.3in-line-formulae description="In-line Formulae" end="tail"?where f1 represents a focal length of the first lens unit, bf represents a back focus in air, and fw represents a focal length of an overall system at a wide angle end, whereby, while downsizing of an overall lens system is achieved, various aberrations accompanying zooming are well corrected, good optical performance is attained over an entire screen, and a wide angle of view and a long back focus are also attained.
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Nakayama Hiroki
Yamasaki Shinji
Canon Kabushiki Kaisha
Lester Evelyn A.
Morgan & Finnegan , LLP
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