Patent ID: 7145732

Claim:
A zoom optical system for forming an optical image of an object onto a light receiving plane of an image sensor for converting the optical image into an electrical signal, and performing zooming by varying distances between lens groups in an optical axis direction, the zoom optical system comprising the lens groups including in the order from an object side: a first lens group having a negative optical power; a second lens group having a positive optical power; and a third lens group having a positive optical power, wherein the first lens group is composed of two or more lens elements including at least one positive lens element and at least one negative lens element, the second lens group is composed of two or more lens elements including at least one positive lens element and at least one negative lens element, and all the lens elements in the first lens group are made of a plastic material, and wherein the zoom optical system satisfies the following conditional formula: 0.15< h 1 /T w where h 1 represents an effective optical path radius of a lens surface closest to the object at a wide-angle end, and T w represents an optical axis distance from an apex of the lens surface closest to the object to the light receiving plane of the image sensor at the wide-angle end when the distance to the object is infinite.