▁pr isms ▁bin oc ular s ▁occasionally ▁need ▁their ▁pr ism ▁sets ▁to ▁be ▁re - aligned ▁to ▁bring ▁them ▁into ▁col lim ation . ▁The ▁fixed ▁alignment ▁in ▁roof - pr ism ▁designs ▁means ▁the ▁bin oc ular s ▁normally ▁will ▁not ▁need ▁re - col lim ation . ▁ ▁Opt ical ▁parameters ▁▁ ▁Bin oc ular s ▁are ▁usually ▁designed ▁for ▁specific ▁applications . ▁These ▁different ▁designs ▁require ▁certain ▁optical ▁parameters ▁which ▁may ▁be ▁listed ▁on ▁the ▁pr ism ▁cover ▁plate ▁of ▁the ▁bin oc ular s . ▁Those ▁parameters ▁are : ▁ ▁Magn ification ▁Given ▁as ▁the ▁first ▁number ▁in ▁a ▁bin oc ular ▁description ▁( e . g . ▁ 7 x 3 5 , ▁ 8 x 5 0 ), ▁magn ification ▁is ▁the ▁ratio ▁of ▁the ▁foc al ▁length ▁of ▁the ▁objective ▁divided ▁by ▁the ▁foc al ▁length ▁of ▁the ▁e y ep ie ce . ▁This ▁gives ▁the ▁magn ifying ▁power ▁of ▁bin oc ular s ▁( s ometimes ▁expressed ▁as ▁" d iam eters "). ▁A ▁magn ification ▁factor ▁of ▁ 7 , ▁for ▁example , ▁produces ▁an ▁image ▁ 7 ▁times ▁larger ▁than ▁the ▁original ▁seen ▁from ▁that ▁distance . ▁The ▁des irable ▁amount ▁of ▁magn ification ▁depends ▁upon ▁the ▁intended ▁application , ▁and ▁in ▁most ▁bin oc ular s ▁is ▁a ▁permanent , ▁non - ad just able ▁feature ▁of ▁the ▁device ▁( zo om ▁bin oc ular s ▁are ▁the ▁exception ). ▁Hand - h eld ▁bin oc ular s ▁typically ▁have