obtaining {HEAD ~ a focus position} of {TAIL ~ the object} with respect to the optical system based on the evaluation function calculation values 
of
obtaining { HEAD ~ a focus position } of { TAIL ~ the object } with respect to the optical system based on the evaluation function calculation values
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH