Patent ID: 7751125

Claim:
A zoom lens comprising, in order from an object side, a first lens unit of positive optical power, a second lens unit of negative optical power, a third lens unit of positive optical power, and a fourth lens unit of positive optical power, wherein, when zooming from a wide-angle end to a telephoto end, the first lens unit and the second lens unit move so as to trace a convex path toward an image side, and the third lens unit and the fourth lens unit move monotonously toward the object side, wherein the first lens unit is placed on a position close to the object side at the telephoto end in relation to a position at the wide-angle end, wherein the fourth lens unit consists of a single lens element of positive optical power, the single lens element being a bi-convex lens element, wherein when in a state of focusing at infinity, a focal length of the entire lens system at the wide-angle end is f w , a focal length of the fourth lens unit is f G4 , and a magnification change ratio between the wide-angle end and the telephoto end is Z, where the following two conditions are satisfied: 0.25 <f W /f G4 <0.35, and Z>4.5, and wherein, when in a state of focusing at infinity, a magnification change ratio between the wide-angle end and the telephoto end is Z, a thickness of an i-th lens unit (where i is an integer) is d i , and a total thickness of the lens units is d si , the following condition is satisfied: 3 <d si /Z <5.