Patent ID: 7369323

Claim:
A zoom lens system that forms an optical image of an object with a variable magnification, in order from the object side, comprising a first lens unit of negative optical power, a second lens unit of positive optical power and a third lens unit of positive optical power, wherein the lens units move respectively along an optical axis so that a magnification is changed with changing a distance between the respective lens units, the first lens unit, in order from the object side, comprises a first lens element having a negative meniscus shape with the surface of strong curvature facing the image side and a second lens element which is a positive lens element with the surface of strong curvature facing the object side, the second lens unit comprises at least three lens elements including an object side lens element of the second lens unit which is a positive lens element arranged on the most object side with the surface of strong curvature facing the object side and an image side lens element of the second lens unit which is a positive lens element arranged on the most image side with the convex surface facing the object side, the third lens unit comprises solely one positive lens element, in magnification change from a wide-angle limit to a telephoto limit, the first lens unit moves with locus of a convex to the image side, while the second lens unit monotonically moves to the object side, and the following condition is satisfied; | L W −L T |/L W <0.1 (where, Z=f T /f W >2.5) (1) in which, L W is an entire optical length at a wide-angle limit, L T is an entire optical length at a telephoto limit, f T is a focal length of the entire lens system at a telephoto limit, and f W is a focal length of the entire lens system at a wide-angle limit.