▁scale ▁and ▁magn ify ▁them ▁back ▁up ▁to ▁get ▁an ▁image ▁on ▁a ▁camera . ▁A ▁l ens ▁is ▁usually ▁made ▁of ▁a ▁sol en oid ▁co il ▁nearly ▁surrounded ▁by ▁fer romagnet ic ▁materials ▁designed ▁to ▁concent rate ▁the ▁co il ' s ▁magnetic ▁field ▁into ▁a ▁precise , ▁conf ined ▁shape . ▁When ▁an ▁electron ▁enters ▁and ▁leaves ▁this ▁magnetic ▁field , ▁it ▁spir als ▁around ▁the ▁cur ved ▁magnetic ▁field ▁lines ▁in ▁a ▁way ▁that ▁acts ▁very ▁much ▁as ▁an ▁ordinary ▁glass ▁l ens ▁does ▁for ▁light — it ▁is ▁a ▁conver ging ▁l ens . ▁But , ▁unlike ▁a ▁glass ▁l ens , ▁a ▁magnetic ▁l ens ▁can ▁very ▁easily ▁change ▁its ▁foc using ▁power ▁simply ▁by ▁adjust ing ▁the ▁current ▁passing ▁through ▁the ▁co ils . ▁This ▁provides ▁a ▁flex ibility ▁of ▁operation ▁that ▁gets ▁further ▁multip lied ▁when ▁the ▁l enses ▁are ▁assemble d ▁into ▁stack s ▁of ▁independent ▁l enses , ▁each ▁of ▁which ▁can ▁focus , ▁def ocus , ▁magn ify , ▁and / or ▁col lim ate ▁the ▁beam ▁coming ▁from ▁the ▁previous ▁l ens . ▁This ▁allows ▁a ▁single ▁l ens ▁system , ▁between ▁the ▁source ▁and ▁the ▁sample ▁( the ▁" cond enser ▁l ens " ▁system ) ▁to ▁produce ▁a ▁parallel ▁beam ▁over ▁ 1 ▁millimeter ▁in ▁diameter , ▁a ▁tight ly ▁focused ▁beam ▁smaller ▁than ▁an ▁atom , ▁or ▁anything ▁in ▁between . ▁An ▁additional ▁l ens ▁stack , ▁the ▁" inter mediate / project or " ▁l ens ▁system