▁be ▁viewed . ▁ ▁Exit ▁pup il ▁Bin oc ular s ▁concent rate ▁the ▁light ▁gathered ▁by ▁the ▁objective ▁into ▁a ▁beam ▁whose ▁diameter , ▁the ▁exit ▁pup il , ▁is ▁the ▁objective ▁diameter ▁divided ▁by ▁the ▁magn ifying ▁power . ▁For ▁maximum ▁effective ▁light - g ather ing ▁and ▁bright est ▁image ▁and ▁to ▁maxim ize ▁the ▁sharp ness , ▁the ▁exit ▁pup il ▁should ▁at ▁least ▁equal ▁the ▁diameter ▁of ▁the ▁pup il ▁of ▁the ▁human ▁eye ▁— ▁about ▁ 7   mm ▁at ▁night ▁and ▁about ▁ 3   mm ▁day time , ▁reducing ▁with ▁age . ▁If ▁the ▁cone ▁of ▁light ▁streaming ▁out ▁of ▁the ▁bin oc ular s ▁is ▁larger ▁than ▁the ▁pup il ▁it ▁is ▁going ▁into , ▁any ▁light ▁larger ▁than ▁the ▁pup il ▁is ▁was ted . ▁In ▁day time ▁use ▁the ▁human ▁pup il ▁is ▁typically ▁dil ated ▁about ▁ 3   mm , ▁which ▁is ▁about ▁the ▁exit ▁pup il ▁of ▁a ▁ 7 × 2 1 ▁bin oc ular . ▁Much ▁larger ▁ 7 × 5 0 ▁bin oc ular s ▁will ▁produce ▁a ▁cone ▁of ▁light ▁bigger ▁than ▁the ▁pup il ▁it ▁is ▁entering , ▁and ▁this ▁light ▁will , ▁in ▁the ▁day time , ▁be ▁was ted . ▁An ▁exit ▁pup il ▁that ▁is ▁too ▁small ▁will ▁also ▁present ▁an ▁observer ▁with ▁a ▁dim mer ▁view ▁since ▁only ▁a ▁small ▁portion ▁of ▁the ▁light ▁gather ing ▁surface ▁of ▁the ▁ret ina ▁is ▁used . ▁For ▁applications ▁where ▁equipment ▁has ▁to