Patent ID: 7907355

Claim:
A zoom lens system, comprising, in order from an object side to an image side: a first lens unit that has a positive optical power and does not move for zooming, the first lens unit comprising, in order from the object side to the image side: a front subunit that has a negative optical power and does not move for focusing; a middle subunit that has a positive optical power and moves during the focusing; and a rear subunit that has a positive optical power and does not move for the focusing; a second lens unit that has a negative optical power and moves during the zooming; a third lens unit that has a negative optical power and moves during the zooming; and a fourth lens unit that has a positive optical power and does not move for the zooming, wherein the first lens unit further comprises a variable apex angle prism on the image side of the front subunit, wherein the front subunit includes at least one negative lens element and at least one positive lens element, and wherein the following condition is satisfied 26 <νd 1 −νd 2<70, where νd 1 denotes an average Abbe number of material of the at least one negative lens element included in the front subunit, and νd 2 denotes an average Abbe number of material of the at least one positive lens element included in the front subunit.