Patent ID: 8390943

Claim:
An optical system, comprising, in order from an object side thereof: a first lens group that remains fixed, an aperture stop, a second lens group that remains fixed and has positive refracting power, and a third lens group that includes one or a cemented, first lens, is movable and has negative refracting power, wherein: the third lens group moves along an optical axis toward an image side thereby implementing focusing from a focusing-on-infinity state to a focusing-on-a-near-distance state, with satisfaction of the following Conditions (1) and (2): | f (2+3)g /f 1g |<1 (1) −6.0<( R 3gr +R 3gf )/( R 3gr −R 3gf )<3.5 (2) where f (2+3)g is a combined focal length of the second lens group and the third lens group upon focusing on infinity, f 1g is a focal length of the first lens group, R 3gr is an axial radius of curvature of a surface in and on the most image side of a negative lens component forming a part of the third lens group, and R 3gf is an axial radius of curvature of a surface in and on the most object side of the lens component forming a part of the third lens group.