Patent ID: 7417801

Claim:
An image pickup optical system for forming a light flux from an object into an optical image on an image pickup element, the image pickup optical system comprising, in order from an object side thereof: a first lens group having a positive power; a second lens group having a negative power; a third lens group having a positive power; and a fourth lens group having a positive power which consists of, in order from the object side, a front group with a negative power and a rear group with a positive power, wherein the first lens group moves to the object side and a distance between each neighboring lens groups changes, for varying a power of the image pickup optical system from a wide-angle end to a telephoto end, one group between the front group and the rear group in the fourth lens group consists of one lens which moves substantially perpendicular to an optical axis for a shake compensation, and the image pickup optical system fulfills following conditional formulas: 5 <f 1 /fw <20, 0.01 <f 3 /f 4<0.6, where f 1 is a focal length of the first lens group, fw is a focal length of the image pickup optical system at the wide-angle end, f 3 is a focal length of the third lens group, and f 4 is a focal length of the fourth lens group.