Inner focus lens system, interchangeable lens apparatus and camera system

An inner focus lens system having a plurality of lens units each being composed of at least one lens element, the inner focus lens system therein comprising eight or more lens elements, wherein:

• in the lens system being focused from an infinity in-focus condition to a close-object in-focus condition, a lens unit located closest to an object side of the lens system is, with respect to an image surface for the lens system, fixed;
• the lens unit located closest to the object side of the lens system includes a first lens element located closest to the object side, and a second lens element located, relative to the first lens element, on an image side of the lens system;
• and
• the lens system satisfies following conditions (1) and (3):
• BF/Y<1.7 (1)
• 0<|(r2a+r1b)/(r2a−r1b)|<1 (3)
• where
• BF is distance from an apex of an image side surface of a lens element located closest to the image side in the lens system, to the image surface,
• Y is maximum image height,
• r1b is radius of curvature of an image-side surface of the first lens element, and
• r2a is radius of curvature of an object-side surface of the second lens element.