Patent ID: 6825989
Filing Date: 2004-11-30
Classification: G02B

Abstract:
A zoom lens system comprising, in order from an object side thereof, a first lens group which is movable along an optical axis of said zoom lens system during zooming and has positive refracting power, a second lens group having negative refracting power, wherein a spacing between the first lens group and the second lens group becomes wide upon zooming from a wide-angle end to a telephoto end of said zoom lens system and a rear lens group having at least two movable subgroups, wherein a focal length f1 of said first lens group and anomalous dispersion &Dgr;&thgr;gF of at least one positive lens element in said first lens group satisfy the following conditions:6<f1/L<20â€ƒâ€ƒ(1) 0.015gF<0.1â€ƒâ€ƒ(2) where L is a diagonal length of an effective image pickup surface located in the vicinity of an image-formation plane, and the anomalous dispersion &Dgr;&thgr;gF of each medium (vitreous material) is defined by&thgr;gF=AgF+BgFÂ·&ngr;d+&Dgr;&thgr;gF with the proviso that &thgr;gF=(ngâˆ’nF)/(nFâˆ’nC) and &ngr;d=(ndâˆ’1)/(nFâˆ’nC) wherein nd, nF, nC and ng are refractive indices with respect to d-line, F-line, C-line and g-line, respectively, and AgF and BgF are each a linear coefficient determined by two vitreous material types represented by glass code 511605 (available under the trade name of NSL7, Ohara Co., Ltd. with &thgr;gF=0.5436 and &ngr;d=60.49) and glass code 620363 (available under the trade name of PBM2, Ohara Co., Ltd. with &thgr;gF=0.582 and &ngr;d=36.26); AgF is 0.641462485 and BgF is âˆ’0.001617829.