Thus, {TAIL ~ a signal} proportional to the total amount of light received by the photo detecting elements 6a and 6b is supplied to {HEAD ~ the light intensity control circuit D} 
Thus , { TAIL ~ a signal } proportional to the total amount of light received by the photo detecting elements 6a and 6b is supplied to { HEAD ~ the light intensity control circuit D }
OTH OTH 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 HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD