Patent ID: 8767319

Claim:
An inner-focus large-aperture medium-telephoto lens system comprising, as lens groups, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group in order from an object side, wherein for focusing on a close-distance object, the first and third lens groups remain stationary relative to an image surface and the second lens group moves toward the object side, the second lens group includes only one negative lens element and at least includes, in order from the object side, a positive lens element, a negative lens element, and a positive lens element, and conditional formula (1) below is fulfilled: −0.5<( R 1 +R 2)/( R 1 −R 2)<−0.1 (1) where R 1 represents a radius of curvature of an object-side surface of the negative lens element in the second lens group; and R 2 represents a radius of curvature of an image-side surface of the negative lens element in the second lens group.