Patent ID: 7215482

Claim:
A variable magnification optical system which forms optical images of objects on the light-receptive surface of an image pickup device for converting optical images into electrical signals and performs magnification by varying the spacing of respective lens groups in the optical axis direction, said optical system comprising from the object side: a first lens group including plural lenses and at least one aspherical surface and having a negative optical power; and a second lens group having a positive optical power, wherein the spacing between the first lens group and the second lens group is reduced for magnification from the wide-angle end to the telephoto end and the following conditions are satisfied, ΔN1max≧0.35 0.7 <f 2/ fw< 2 Lb/fw< 1 where ΔN 1 max: the maximum value, out of the absolute values of the refractive index difference between two lenses, for all possible combinations of two lenses out of the lenses of the first lens group, f 2 : the total focal length of the second lens group, fw: the total focal length of the entire optical system at the wide-angle end, Lb: the distance between the peak point of the lens surface having a power which is most proximal to the image pickup device and the surface of the image pickup device along the optical axis at the telephoto end.