Patent ID: 8611019

Claim:
A zoom lens system, in order from an object side to an image side, comprising a first lens unit having negative optical power, a second lens unit having positive optical power, a third lens unit having negative optical power, and a fourth lens unit having positive optical power, wherein: the first lens unit and the third lens unit move along an optical axis, and the fourth lens unit is fixed with respect to an image surface, in zooming from a wide-angle limit to a telephoto limit at a time of image taking, the third lens unit moves along the optical axis, in focusing from an infinity in-focus condition to a close-object in-focus condition, and the following conditions (1) and (2) are satisfied: 0.0 <|M 3 /f W |<0.5 (1), and 0.2 <|f 3 /f 4 |<1.0 (2), where M 3 is an amount of movement of the third lens unit, in zooming from a wide-angle limit to a telephoto limit at the time of image taking, f 3 is a composite focal length of the third lens unit, f 4 is a composite focal length of the fourth lens unit, and f W is a focal length of the zoom lens system at a wide-angle limit.