Patent ID: 8259217

Claim:
A fast focusing method for a digital camera, for adjusting a focusing focal length to a target focal length by the digital camera in an auto focusing stage, the focusing method comprising: loading a completion time of a previous focusing as a first time (T 1 ) and a reference focal length; capturing a system time before a current focusing as a second time (T 2 ); performing a fuzziness detection procedure to acquire a focus value when a difference obtained by subtracting the first time from the second time (ΔT=T 2 −T 1 ) is greater than a focusing time threshold; and performing following steps when the focus value falls between a lower limit focusing threshold and an upper limit focusing threshold: setting a focusing focal length range covering the reference focal length; capturing corresponding comparison images at different focusing focal lengths respectively in the focusing focal length range; calculating a contrast value of each of the comparison images; and selecting a maximum value from the contrast values and setting a focal length corresponding to the selected contrast value as the target focal length.