▁polar ized ▁in ▁the ▁plane ▁of ▁inc idence ▁( p - pol ar ized ) ▁and ▁light ▁polar ized ▁orthogonal ▁to ▁the ▁plane ▁of ▁inc idence ▁( s - pol ar ized ) ▁experience ▁different ▁phase ▁sh ifts . ▁ ▁As ▁a ▁consequence , ▁linear ly ▁polar ized ▁light ▁emer ges ▁from ▁a ▁roof ▁pr ism ▁elli pt ically ▁polar ized . ▁ ▁Furthermore , ▁the ▁state ▁of ▁elli pt ical ▁polar ization ▁of ▁the ▁two ▁paths ▁through ▁the ▁pr ism ▁is ▁different . ▁ ▁When ▁the ▁two ▁paths ▁re comb ine ▁on ▁the ▁ret ina ▁( or ▁a ▁det ector ) ▁there ▁is ▁inter ference ▁between ▁light ▁from ▁the ▁two ▁paths ▁causing ▁a ▁dist ort ion ▁of ▁the ▁Point ▁Sp read ▁Function ▁and ▁a ▁d eter ior ation ▁of ▁the ▁image . ▁ ▁Resol ution ▁and ▁contrast ▁suffer . ▁ ▁These ▁unw anted ▁inter ference ▁effects ▁can ▁be ▁suppress ed ▁by ▁v apor ▁depos iting ▁a ▁special ▁die lect ric ▁co ating ▁known ▁as ▁a ▁phase - cor re ction ▁co ating ▁or ▁p - co ating ▁on ▁the ▁roof ▁surfaces ▁of ▁the ▁roof ▁pr ism . ▁This ▁co ating ▁elimin ates ▁the ▁difference ▁in ▁phase ▁shift ▁between ▁s - ▁and ▁p - ▁polar ization ▁so ▁both ▁paths ▁have ▁the ▁same ▁polar ization ▁and ▁no ▁inter ference ▁de gr ades ▁the ▁image . ▁ ▁A ▁met all ic ▁co ating ▁on ▁the ▁roof ▁surfaces ▁also ▁elimin ates ▁the ▁phase ▁shift ▁( although ▁not ▁completely ). ▁ ▁Met all ic ▁coat ings ▁are