Patent ID: 8503096

Claim:
An inner focus lens, 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; and a third lens unit having positive optical power, wherein the second lens unit is moved along an optical axis so that focusing from an infinite-distance object side to a short-distance object side is achieved, the first lens unit includes a bi-convex air lens, and the following conditions (1) and (2) are satisfied: 0.65<| f 2 /f|< 5.00 (1) 0.5< f 23 /f 1 <9.0 (2) where, f 2 is a focal length of the second lens unit, f is a focal length of the entire system in an infinity in-focus condition, f 23 is a composite focal length of the second lens unit and the third lens unit in an infinity in-focus condition, and f 1 is a focal length of the first lens unit.