Patent ID: 8917455

Claim:
A variable power optical system comprising, in order from an object side, a first lens group with negative refractive power, a second lens group with positive refractive power, a third lens group with negative refractive power, and a fourth lens group with positive refractive power, wherein the first lens group consists of, in order from the object side, one negative lens and one positive lens with an air space therebetween that is made to keep still in changing magnification, and the following conditions are satisfied: 1.75 ≦Nd 1 g≦ 2.50 15 ≦Vd 1 g≦ 43 3 ≦VdN−VdP≦ 28 where Nd1g denotes a refractive index of each of the lenses constituting the first lens group, with respect to the d line, Vd1g denotes an Abbe's Number of each of the lenses constituting the first lens group, with respect to the d line, VdN denotes an Abbe's Number of the negative lens in the first lens group, with respect to the d line, and VdP denotes the Abbe's Number of the positive lens in the first lens group, with respect to the d line, and wherein the fourth lens group comprises a positive lens, and satisfies the following condition: 10 ≦Vd 4 g ≦40 where Vd4g denotes an Abbe's Number of the positive lens of the fourth lens group with respect to the d line.