▁the ▁optical ▁axis ▁before ▁the ▁foc using ▁l ens . ▁This ▁is ▁usually ▁realized ▁by ▁a ▁simple ▁correction ▁system ▁consisting ▁of ▁two ▁pairs ▁of ▁co ils . ▁By ▁adjust ing ▁the ▁curr ents ▁in ▁these ▁co ils ▁any ▁required ▁correct ing ▁field ▁can ▁be ▁produced . ▁ ▁After ▁passing ▁the ▁foc using ▁l ens , ▁the ▁beam ▁can ▁be ▁applied ▁for ▁w eld ing , ▁either ▁directly ▁or ▁after ▁being ▁def lect ed ▁by ▁a ▁def lection ▁system . ▁This ▁consists ▁of ▁two ▁pairs ▁of ▁co ils , ▁one ▁for ▁each ▁X ▁and ▁Y ▁direction . ▁These ▁can ▁be ▁used ▁for ▁" static " ▁or ▁" dynamic " ▁def lection . ▁St atic ▁def lection ▁is ▁useful ▁for ▁exact ▁position ing ▁of ▁the ▁beam ▁by ▁w eld ing . ▁Dynamic ▁def lection ▁is ▁realized ▁by ▁supp lying ▁the ▁def lection ▁co ils ▁with ▁curr ents ▁which ▁can ▁be ▁controlled ▁by ▁the ▁computer . ▁This ▁opens ▁new ▁possibilities ▁for ▁electron - be am ▁applications , ▁like ▁surface ▁hard ening ▁or ▁an ne aling , ▁exact ▁beam ▁position ing , ▁etc . ▁ ▁The ▁fast ▁def lection ▁system ▁can ▁also ▁be ▁applied ▁( if ▁provided ▁with ▁appropriate ▁electron ics ) ▁for ▁imag ing ▁and ▁eng ra ving . ▁In ▁this ▁case ▁the ▁equipment ▁is ▁operated ▁like ▁a ▁sc anning ▁electron ▁mic ros cope , ▁with ▁a ▁resolution ▁of ▁about ▁ 0 , 1   mm ▁( limited ▁by ▁the ▁beam ▁diameter ). ▁In ▁a ▁similar ▁mode ▁the ▁fine ▁computer - control led ▁beam ▁can ▁"