Importance

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Abstract

A projection zoom lens is constituted by: a negative first lens group; a positive moving second lens group; a positive moving third lens group; a positive final lens group; at least one lens group positioned between the final lens group and the third lens group; and an aperture stop provided between adjacent moving lens groups. The aperture stop is a variable stop, of which the aperture diameter changes such that the numerical aperture of the zoom lens becomes constant. The zoom lens satisfies Conditional Formulae below:

description='In-line Formulae' end='lead'2.8<Bf/Imφ  (1′)description='In-line Formulae' end='tail'

description='In-line Formulae' end='lead'L/Imφ<12  (2)description='In-line Formulae' end='tail'

wherein Bf is the back focus of the entire system at the reduction side at the wide angle end, Imφ is the maximum effective image circle diameter at the reduction side, and L is the distance from the lens surface most toward the magnification side to the lens surface most toward the reduction side when the projection distance is infinity.

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First Claim