The second reflecting surface can be rotated around its longitudinal axis, thereby the second reflecting surface can be inserted in or removed from {TAIL ~ an optical path} of {HEAD ~ light} traveling from the light source to the first reflecting surface 
The second reflecting surface can be rotated around its longitudinal axis , thereby the second reflecting surface can be inserted in or removed from { TAIL ~ an optical path } of { HEAD ~ light } traveling from the light source to the first reflecting surface
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH