US Patent 7548269 System for autofocusing a moving object

The present invention provides an autofocus system for controlling the focus of a taking lens by specifying a subject to be autofocused within an AF area, which is part of the field of view of a camera, and automatically focusing on the subject, comprising: a target subject specifying device which specifies a target subject to be focused, a target subject movement detection device which detects the movement of the target subject specified by the target subject specifying device, within the field of view, and an AF-area altering device which alters the extent of the AF area to track the movement of the target subject detected by the target subject movement detection device.