The main optical housing 56 includes a viewing aperture 68 serving as {HEAD ~ an entrance pupil region} to enable light from the object being viewed to pass into {TAIL ~ the reflecting assemblies} of the optical system 
The main optical housing 56 includes a viewing aperture 68 serving as { HEAD ~ an entrance pupil region } to enable light from the object being viewed to pass into { TAIL ~ the reflecting assemblies } of the optical system
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH