Patent ID: 8130453

Claim:
A zoom lens system, in order from an object side to an image side, comprising: a first lens unit having positive optical power; a second lens unit having negative optical power; a third lens unit having negative optical power; and a fourth lens unit having positive optical power, wherein at the time of zooming, all lens units move in a direction along the optical axis such that intervals among respective lens units vary, at the time of zooming, the third lens unit moves in the direction along the optical axis such that the interval between the second lens unit and the third lens unit is made longer at a telephoto limit than the interval at a wide-angle limit, and the following conditions are satisfied: −1.26 <=f F /f 4α <−0.7 (6) −20 <f 2 *( f T /f W )/√( f W *f T )<−6 (8) where, f F is a focal length of a focusing lens unit, and f 4α is a composite focal length of the fourth lens unit and a lens unit subsequent thereto at a wide-angle limit, f 2 is a focal length of the second lens unit, f T is a focal length of an entire system at a telephoto limit, and f W is a focal length of the entire system at a wide-angle limit.