obtaining a plurality of evaluation function calculation values in {HEAD ~ a variety} of optical positions by repeating the steps for calculating the gray level data of the left and right areas, obtaining the gray level ratio, and calculating the evaluation function through variation of {TAIL ~ the optical position} of the object; and 
obtaining a plurality of evaluation function calculation values in { HEAD ~ a variety } of optical positions by repeating the steps for calculating the gray level data of the left and right areas , obtaining the gray level ratio , and calculating the evaluation function through variation of { TAIL ~ the optical position } of the object ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH