Patent ID: 8503090

Claim:
A zoom optical system, which comprises, in order from an object side thereof, a first lens group, a second lens group and a third lens group and adapted to implement zooming by varying a spacing between the lens groups, and in which there is a lens group that is located on an image plane side with respect to a stop, includes a plurality of lenses and has a positive refracting power as a whole, wherein the lens group having positive refracting power includes therein a first lens and a second lens in order from the object side, an image plane side surface of the first lens is convex toward the object side, and an object side surface of the second lens is concave toward the object side, with satisfaction of the following Condition (1): −0.5≦( Ra 1+ Ra 2)/( Ra 1− Ra 2)≦0.5 (1) where Ra 1 is a radius of curvature of the image plane side surface of the first lens, and Ra 2 is a radius of curvature of the object side surface of the second lens.