Patent ID: 7683975

Claim:
An automatic focusing apparatus comprising: a liquid crystal lens whose focal length varies with an applied voltage; a liquid crystal lens driving unit which applies a prescribed voltage to said liquid crystal lens; an optical-to-electrical converter which produces an image signal from an optical image passed through said liquid crystal lens; a temperature sensor which detects temperature near said liquid crystal lens; and a control unit which can extract a plurality of focus signals either in accordance with focus signal collective extraction control in which the image signal output from said optical-to-electrical converter is sampled with said image signal acquisition period while causing said liquid crystal lens to undergo a transient response by applying said prescribed voltage by controlling said liquid crystal lens driving unit, or in accordance with focus signal successive extraction control in which the image signal output from said optical-to-electrical converter is sampled after liquid crystal in said liquid crystal lens has fully responded to the voltage applied to said liquid crystal lens when said voltage is varied by controlling said liquid crystal lens driving unit, wherein said control unit selects either said focus signal collective extraction control or said focus signal successive extraction control based on said temperature or on said image signal acquisition period, and controls said liquid crystal lens driving unit based on said extracted plurality of focus signals so that a maximum focus signal is achieved.