obtaining {HEAD ~ a plurality} of {TAIL ~ evaluation function calculation values} in 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 the optical position of the object; and 
of
obtaining { HEAD ~ a plurality } of { TAIL ~ evaluation function calculation values } in 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 the optical position of the object ; and
OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH