Patent ID: 7345706

Claim:
An auto focus system, comprising: a plurality of image pickup devices which pick up images of object light incident on a picture-taking lens and are arranged at positions of different light path lengths; a focus evaluation value generation device which generates a focus evaluation value indicating a degree of sharpness of the image picked up by each of the image pickup devices; a corrector which makes a correction on sensitivity of the focus evaluation value obtained from each of the image pickup devices so that the sensitivities match up; and a focus control device which moves a focus of the picture-taking lens to a focusing position according to the focus evaluation values, wherein a value obtained by, for each focus evaluation value obtained from each of the image pickup devices, multiplying a variation of the focus evaluation value from a predetermined reference value by a predetermined gain is the focus evaluation value used for controlling the focus of the picture-taking lens; and the corrector makes a correction on the sensitivity by setting the reference value and the gain at appropriate values, and includes: a reference value setting device which sets as the reference value the focus evaluation value obtained from each of the image pickup devices in a case where an image having no contrast is picked up; and a gain setting device which sets the gain so that a maximum value of the focus evaluation value obtained from each of the image pickup devices matches up in a case where the focus of the picture-taking lens is moved, wherein, at the time of having the gain set by the gain setting device, the corrector moves the focus in a state in which a zoom of the picture-taking lens is set at a predetermined position.