Zoom lens system

Claim 1

A zoom lens system comprising a lens group having positive refractive power and another lens group having negative refractive power, and so adapted as to perform variation of focal length by varying the airspace reserved between said lens groups, said lens group having the positive refractive power comprising at least one graded refractive index lens component having the shape of a negative meniscus lens and a refractive index distribution wherein refractive indices are lowered as the lens portions are farther from the optical axis in the direction perpendicular to the optical axis and, when the refractive index distribution of said graded refractive index lens is given by the following formula, said zoom lens system satisfying the following condition (1): n(y).sub.d =N.sub.0.sbsb.d +N.sub.1.sbsb.dy.sup.2 +N.sub.2.sbsb.dy.sup.4 +. . . -12<N.sub.1.sbsb.d.f.sub.w.sup.2 <-0.5 (1) wherein the reference symbol y represents distance from the optical axis in the direction perpendicular to the optical axis, the reference symbol n(y) d designates refractive index for the d-line at the distance y, the reference symbol N 0d denotes refractive index for the d-line on the optical axis, the reference symbol N 1d , N 2d , . . . represent the coefficients of refractive index distribution for the d-line, and the reference symbol f W designates focal length of the zoom lens system as a whole at the wide position thereof.