Patent ID: 8643960

Claim:
An internal focus lens comprising sequentially from an object side: a first lens group having a positive refractive power; a second lens group having a negative refractive power; and a third lens group having a positive refractive power, wherein the second lens group is configured by a simple lens element, the second lens group is moved along an optical axis to perform focusing, and condition expressions (1) and (2) are satisfied: 0.48 <|f 3 |/f< 0.73 (1) 1.05 <Fno×f 1 /f< 1.42 (2) where, f3 is the focal length of the third lens group, f is the focal length of the entire optical system, f1 is the focal length of the first lens group, and Fno is the F number of the entire optical system.