Patent ID: 8654448

Claim:
An inner focus lens system comprising, in order from an object side to an image side: a first lens unit having a positive refractive power; an aperture stop; a second lens unit having a positive refractive power; and a third lens unit, wherein the total number of lens units in the inner focus lens system is three, the three lens units including the first lens unit, the second lens unit, and the third lens unit, the first lens unit comprises a plurality of negative lenses and at least one positive lens, the lens located closest to the object side in the first lens unit being one negative lens among the plurality of negative lenses, the second lens unit includes at least one negative lens and at least one positive lens, for focusing from an infinite object distance to a close object distance, the second lens unit moves toward the object side in such a way that the distance between the second lens unit and the aperture stop decreases and that the distance between the second lens unit and the third lens unit increases, and the lens system satisfies the following conditional expressions (1) and (2): 1 <f 1 /f< 14 (1), and 0.8 <f 23 /f 2 <3 (2), where f 1 is the focal length of the first lens unit, f is the focal length of the entire inner focus lens system in the state in which the inner focus lens system is focused on an object point at infinity, f 23 is the composite focal length of the second lens unit and the third lens unit in the state in which the lens system is focused on an object at infinity, and f 2 is the focal length of the second lens unit.