By {TAIL ~ changing conditions} of an electron optic system such as potential E0, E1 and E2, the acceleration voltage and electric field on {HEAD ~ the object} are controlled 
By { TAIL ~ changing conditions } of an electron optic system such as potential E0 , E1 and E2 , the acceleration voltage and electric field on { HEAD ~ the object } are controlled
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 OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH