Patent ID: 7212350

Claim:
A zoom optical system that includes a function of preventing blurring of an image comprising, arranged along an optical axis in order from the object side as follows: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power; and a fourth lens group having positive refractive power; wherein said second lens group and said fourth lens group move along the optical axis when zooming the zoom optical system between the wide-angle end and the telephoto end; said fourth lens group moves along the optical axis during focusing of the zoom optical system; said third lens group includes, arranged along the optical axis in order from the object side, a lens element having positive refractive power that performs said function of preventing blurring of an image and that includes at least one aspheric surface, a biconvex lens element, and a biconcave lens element joined with said biconvex lens element to form a lens component; said lens element having positive refractive power performs said function of preventing blurring of an image by moving perpendicular to the optical axis; and the following conditions are satisfied: 0.36<| f 2/( fw·ft ) 0.5 |<0.45 4.3 <f 3/ fw< 7.0 2.0 <bfw/fw< 2.9 where f2 is the focal length of said second lens group, fw is the focal length of the entire zoom optical system at the wide-angle end, ft is the focal length of the entire zoom optical system at the telephoto end, f3 is the focal length of said third lens group, and bfw is the back focal length of the entire zoom optical system.