US Patent 7463425 Zoom lens system

A zoom lens system is disclosed that includes a front first lens group including a first lens of divergent meniscus and a second lens of plano-convex; an intermediate second lens group including a third lens of plano-concave, a fourth lens of plano-concave, and a fifth lens of plano-convex; and a rear third lens group including a sixth lens of double-convex, a seventh lens of double-convex, an eighth lens of plano-concave, and a ninth lens of plano-concave. The sixth and ninth lenses are non-spherical lenses formed of a plastic material, and the zoom lens system satisfies the following conditions (a) 0.16<fw/f1<0.21 (b) −0.78<fw/f2<−0.64 (c) 0.70<fw/f3<0.75 (d) 0.47<log Z3/log Z<0.76.