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