Patent ID: 8564888

Claim:
A variable power optical system comprising, in order from the 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 second lens group comprises at least one positive lens and a negative lens, the fourth lens group comprises a positive lens, and the variable power optical system satisfies the following conditions: 10 ≦Vd 4 g≦ 45 2.2 ≦|α/f 1|+(α/ f 2)−0.026 ×Vd 4 g≦ 5.0 10 ≦Vd max− Vd min≦80 where α=(FLw×FLt) 1/2 , FLw denotes the focal length of the whole of the variable power optical system in the wide angle end position, FLt denotes the focal length of the whole of the variable power optical system in the telephoto end position, f 1 denotes the focal length of the first lens group, f 2 denotes the focal length of the second lens group, Vd 4 g denotes the Abbe' Number of the positive lens of the fourth lens group with respect to the d line, Vdmax denotes the Abbe's Number of a glass material having the lowest dispersion characteristic of those of glass materials which are used for lenses of the second lens group, with respect to the d line, and Vdmin denotes the Abbe's Number of a glass material having the highest dispersion characteristic of those of glass materials which are used for lenses of the second lens group, with respect to the d line.