▁different ▁methods ▁are ▁used ▁to ▁turn ▁the ▁image ▁right ▁way ▁up . ▁ ▁Bin oc ular s ▁with ▁ere ct ing ▁l enses ▁▁ ▁In ▁apr ism atic ▁bin oc ular s ▁with ▁Ke pler ian ▁opt ics ▁( which ▁were ▁sometimes ▁called ▁" t win ▁teles cop es ") ▁each ▁t ube ▁has ▁one ▁or ▁two ▁additional ▁l enses ▁( rel ay ▁l ens ) ▁between ▁the ▁objective ▁and ▁the ▁oc ular . ▁These ▁l enses ▁are ▁used ▁to ▁ere ct ▁the ▁image . ▁The ▁bin oc ular s ▁with ▁ere ct ing ▁l enses ▁had ▁a ▁serious ▁dis adv antage : ▁they ▁are ▁too ▁long . ▁Such ▁bin oc ular s ▁were ▁popular ▁in ▁the ▁ 1 8 0 0 s ▁( for ▁example , ▁G . & ▁S . ▁Mer z ▁models ), ▁but ▁became ▁ob sole te ▁shortly ▁after ▁the ▁Karl ▁Ze iss ▁company ▁introduced ▁improved ▁pr ism ▁bin oc ular s ▁in ▁the ▁ 1 8 9 0 s . ▁ ▁Pr ism ▁bin oc ular s ▁▁ ▁Opt ical ▁pr isms ▁added ▁to ▁the ▁design ▁enabled ▁the ▁display ▁of ▁the ▁image ▁the ▁right ▁way ▁up ▁without ▁need ing ▁as ▁many ▁l enses , ▁and ▁decre asing ▁the ▁overall ▁length ▁of ▁the ▁instrument , ▁typically ▁using ▁a ▁Por ro ▁pr ism ▁or ▁roof - pr isms . ▁ ▁Por ro ▁pr ism ▁bin oc ular s ▁ ▁Por ro ▁pr ism ▁bin oc ular s ▁are ▁named ▁after ▁Italian ▁opt ician ▁Ign az io ▁Por ro , ▁who