The distance between {HEAD ~ two sensing chip} 31, 32 is represented by L2, and {TAIL ~ the distance} between two light focusing means 16, 16 is represented by L1 
The distance between { HEAD ~ two sensing chip } 31 , 32 is represented by L2 , and { TAIL ~ the distance } between two light focusing means 16 , 16 is represented by L1
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH