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