Patent ID: 7760439

Claim:
A zoom optical system, comprising: a first lens group having a negative optical power; and a second lens group having a positive optical power in the order from an object side, a distance between the first lens group and the second lens group being decreased in zooming from a wide angle end to a telephoto end, wherein the first lens group includes at least one negative lens element and at least one positive lens element, the second lens group is constituted of three or less lens elements, and the zoom optical system satisfies the conditional expressions (1) and (2): 0.5< D 1/ fw< 0.8 (1) 0.7< f 2/ fw< 2.0 (2) where D 1 : a thickness of the first lens group on an optical axis from a forwardmost lens surface to a rearmost lens surface, fw: a composite focal length of an entirety of the optical system at the wide angle end, and f 2 : a composite focal length of the second lens group, wherein the second lens group is constituted of a positive lens element and a negative lens element in the order from the object side, and the zoom optical system satisfies the conditional expression (8): 0.7<| f 2 n/f 2 p |<1.8 (8) where f 2 p: a focal length of the positive lens element in the second lens group, and f 2 n: a focal length of the negative lens element in the second lens group, and wherein the second lens group satisfies the conditional expressions (11) and (12): | N 2 p−N 2 n|> 0.15 (11) | v 2 p−v 2 n|> 30 (12) where N 2 p: a refractive index of the positive lens element in the second lens group, v 2 p: the Abbe number of the positive lens element in the second lens group, N 2 n: a refractive index of the negative lens element in the second lens group, and v 2 n: the Abbe number of the negative lens element in the second lens group.