Patent ID: 7755845

Claim:
A zoom lens system comprising: a first lens unit having a positive optical power; a second lens unit having a negative optical power, wherein the second lens unit moves during zooming; a third lens unit having a positive optical power, wherein the third lens unit does not move for zooming; and a fourth lens unit having a positive optical power, wherein the fourth lens unit moves during zooming, wherein the first lens unit, the second lens unit, the third lens unit, and the fourth lens unit are arranged in order from an object side to an image side, and wherein the following conditions are satisfied: 10.0< f 3/ fw< 26.0 1.2< bft/fw< 3.5 where fw is a focal length of the zoom lens system at a wide-angle end, f 3 is a focal length of the third lens unit, and bft is an equivalent air distance of a back focus at a telephoto end, wherein the first lens unit includes three or more positive lens elements, and wherein the following condition is satisfied: 58<νd1 where νd 1 is an average of Abbe numbers of materials of the positive lens elements included in the first lens unit.