Patent ID: 8218961

Claim:
An autofocus system comprising: an image pickup unit that takes a subject image formed by an optical system; a target subject detection unit that detects a target subject, which is previously registered as an autofocus target, in a photographing image taken by the image pickup unit; a lens-to-subject distance calculation unit that calculates a lens-to-subject distance to the target subject based on information on a photographing angle of view depending on a focal length of the optical system, a size of the target subject in the photographing image, and a size of the target subject in real space; a rough AF unit that controls a focus of the optical system so as to bring into focus the subject which is located at the lens-to-subject distance calculated by the lens-to-subject distance calculation unit; and a normal AF unit, wherein the control of the focus is performed by the normal AF unit after the control of the focus is performed once by the rough AF unit and subsequently the size of the target subject in the photographing image does not change in the photographing image.