Patent ID: 7576796
Filing Date: 2009-08-18
Classification: H04N

Abstract:
1. An auto focus system, comprising: two 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; and a focus control device which moves a focus of the picture-taking lens to a focusing position by controlling the focus of the picture-taking lens so that two focus evaluation values generated by the focus evaluation value generation device corresponding to the two image pickup devices, respectively, become equal to each other, wherein the focus control device acquires a ratio (ΔAFV) between the two focus evaluation values, determines a travel distance by multiplying the ΔAFV with a predetermined automatic focusing gain (AFG), if the focus evaluation values indicate a front focus, the travel distance is determined by: (ΔAFV−1)·AFG, adds the travel distance to a current moving target position to a set a new target position, and sets a moving speed of the picture-taking lens based on the ΔAFV between the current moving target position and a current position of the picture-taking lens, and as the picture-taking lens approaches the new target position, the ΔAFV between the focus evaluation values decrease, and the travel distance approaches zero.