wherein {HEAD ~ an incidence angle} of the image beam to the optical lens is between 0 degrees and {TAIL ~ 90 degrees} 
wherein { HEAD ~ an incidence angle } of the image beam to the optical lens is between 0 degrees and { TAIL ~ 90 degrees }
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH REL REL OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL