a mirror unit configured to, as a result of being arranged in {TAIL ~ a light path} of the object light, change the light path of {HEAD ~ the object} light 
a mirror unit configured to , as a result of being arranged in { TAIL ~ a light path } of the object light , change the light path of { HEAD ~ the object } light
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH