▁a ▁magnetic ▁field ▁will ▁cause ▁electrons ▁to ▁move ▁according ▁to ▁the ▁left ▁hand ▁rule , ▁thus ▁allowing ▁for ▁elect romagnet s ▁to ▁manipulate ▁the ▁electron ▁beam . ▁The ▁use ▁of ▁magnetic ▁fields ▁allows ▁for ▁the ▁formation ▁of ▁a ▁magnetic ▁l ens ▁of ▁variable ▁foc using ▁power , ▁the ▁l ens ▁shape ▁origin ating ▁due ▁to ▁the ▁distribution ▁of ▁magnetic ▁flux . ▁Additionally , ▁electro static ▁fields ▁can ▁cause ▁the ▁electrons ▁to ▁be ▁def lect ed ▁through ▁a ▁constant ▁angle . ▁Cou pling ▁of ▁two ▁def lections ▁in ▁oppos ing ▁directions ▁with ▁a ▁small ▁intermediate ▁gap ▁allows ▁for ▁the ▁formation ▁of ▁a ▁shift ▁in ▁the ▁beam ▁path , ▁allowing ▁for ▁beam ▁sh ifting ▁in ▁T EM , ▁which ▁is ▁important ▁for ▁S TE M . ▁From ▁these ▁two ▁effects , ▁as ▁well ▁as ▁the ▁use ▁of ▁an ▁electron ▁imag ing ▁system , ▁sufficient ▁control ▁over ▁the ▁beam ▁path ▁is ▁possible ▁for ▁T EM ▁operation . ▁The ▁optical ▁configuration ▁of ▁a ▁T EM ▁can ▁be ▁rapidly ▁changed , ▁unlike ▁that ▁for ▁an ▁optical ▁mic ros cope , ▁as ▁l enses ▁in ▁the ▁beam ▁path ▁can ▁be ▁enabled , ▁have ▁their ▁strength ▁changed , ▁or ▁be ▁disabled ▁entirely ▁simply ▁via ▁rapid ▁elect rical ▁switching , ▁the ▁speed ▁of ▁which ▁is ▁limited ▁by ▁effects ▁such ▁as ▁the ▁magnetic ▁h yst er esis ▁of ▁the ▁l enses . ▁ ▁Opt ics ▁The ▁l enses ▁of ▁a ▁T EM ▁are ▁what ▁gives ▁it ▁its ▁flex ibility ▁of ▁operating ▁modes ▁and ▁ability ▁to ▁focus ▁be ams ▁down ▁to ▁the ▁atomic