Patent ID: 7236308

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 positive optical power; and a fourth lens unit having positive optical power, wherein, magnification variation is performed by varying distances along an optical axis between at least any two of the lens units, during magnification varying from a wide-angle limit to a telephoto limit, the third lens unit moves to the object side, and the first and second lens units move with locus of a convex to the image side, and 0< M lwm /M lmt <0.32 with Z=f T /f w , where Z is the magnification variation ratio, and where M lwm is an amount of movement of the first lens unit from the wide-angle limit to a middle focal length condition when a shooting distance is ∞, M lmt is an amount of movement of the first lens unit from the middle focal length condition to the telephoto limit when the shooting distance is ∞, the middle focal length condition, f m= √(f w *f T ), f m is defined by the focal length of the entire zoom lens system in the middle focal length condition, f w is the focal length of an entire lens system at the wide-angle limit, and f t is the focal length of the entire lens system at the telephoto limit.