Patent ID: 7777801

Claim:
A method for evaluating effective sampling steps of auto focus to obtain a plurality of effective sampling steps of auto focus for an image pickup device, said image pickup device having a lens, said method comprising steps of: (a) obtaining a maximum focus value FVa and a lens search step number Sa corresponding to the maximum focus value FVa when a focusing test chart is located at a first testing position; (b) obtaining a first depth-of-field boundary step number Sb at said first testing position according to an blur percentage value TH; (c) searching a second testing position of said focusing test chart corresponding to said first depth-of-field boundary step number Sb, and calculating a maximum focus value FVb when said focusing test chart is located at said second testing position; (d) obtaining a second depth-of-field boundary step number Sc at said second testing position according to said blur percentage value TH; and (e) repeating the steps (c) and (d), wherein said Sa, Sb and Sc are effective sampling steps.