Zoom lens system for use with a compact camera

Claim 1

In a zoom lens system for use with a compact camera that comprises, in order from the object side, a first lens group having a positive focal length and a second lens group having a negative focal length and which performs zooming by changing the distance between the first and second lens groups, the improvement wherein said first lens group comprises, in order from the object side, a subgroup 1a of a small power that is composed of a positive first lens and a negative second lens and a subgroup 1b of a large positive power that has a surface of a negative power on the image side, said subgroup 1a having at least one aspheric surface that has a divergent amount of a sphericity with respect to a paraxial radius of curvature satisfying the following condition (5), and said zoom lens system further satisfying the following conditions: ##EQU6## where: N 1a-1 : the refractive index at the d-line of the first lens in subgroup 1a; N 1a-2 : the refractive index at the d-line of the second lens in subgroup 1a; f 1 : the focal length of the first lens group; f 1a : the focal length of subgroup 1a; f 1b : the focal length of subgroup 1b; and Δ 1a : the amount of change in the coefficient of a third-order spherical aberration caused by the aspheric surface in subgroup 1a (i.e., an aberrational coefficient as calculated on the assumption that the focal length of the overall system at the wide-angle end is 1.0);