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