Patent ID: 6031669
Filing Date: 2000-02-29
Classification: G02B

Abstract:
A zoom lens, comprising:(a) at least four lens groups that are movable along an optical axis during zooming from a wide-angle end to a telephoto end, the zoom lens having an aspherical surface, and having no greater number of lens elements than two times the number of movable lens groups in the zoom lens;(b) the movable lens groups including a most objectwise movable lens group having a positive refractive power, a most imagewise movable lens group having negative refractive power, an intermediate movable lens group with positive refractive power disposed between the most objectwise movable lens group and the most imagewise movable lens group, the intermediate lens group comprising a positive lens element cemented to a negative lens element, a second movable lens group with negative refractive power disposed between the most objectwise movable lens group and the intermediate lens group; and(c) the zoom lens having a focal length f.sub.W on the wide-angle end, a focal length f.sub.T at the telephoto end, a back focus B.sub.fW at the wide-angle end, a back focus B.sub.fT at the telephoto end, and a lateral magnification .beta..sub.2W of the second movable lens group at the wide-angle end, the zoom lens satisfying the conditions:0.3<(f.sub.W -B.sub.fW)/(f.sub.T -B.sub.fT)<0.54-1<.beta..sub.2W -0.2.