ep ie ces . ▁This ▁makes ▁it ▁more ▁comfortable ▁to ▁view ▁with ▁an ▁ 8 × 4 0 ▁than ▁an ▁ 8 × 2 5 . ▁A ▁ 1 0 x 5 0 ▁bin oc ular s ▁is ▁better ▁than ▁an ▁ 8 x 4 0 ▁for ▁magn ification , ▁sharp ness ▁and ▁l umin ous ▁flux . ▁Object ive ▁diameter ▁is ▁usually ▁expressed ▁in ▁mill im eters . ▁It ▁is ▁custom ary ▁to ▁categor ize ▁bin oc ular s ▁by ▁the ▁magn ification ▁× ▁the ▁objective ▁diameter ; ▁e . g . ▁ 7 × 5 0 . ▁Sm aller ▁bin oc ular s ▁may ▁have ▁a ▁diameter ▁of ▁as ▁low ▁as ▁ 2 2   mm ; ▁ 3 5   mm ▁and ▁ 5 0   mm ▁is ▁a ▁common ▁diameter ▁for ▁field ▁bin oc ular s ; ▁astronom ical ▁bin oc ular s ▁have ▁diam eters ▁r anging ▁from ▁ 7 0   mm ▁to ▁ 1 5 0   mm . ▁ ▁Field ▁of ▁view ▁The ▁field ▁of ▁view ▁of ▁a ▁pair ▁of ▁bin oc ular s ▁depends ▁on ▁its ▁optical ▁design ▁and ▁in ▁general ▁is ▁in vers ely ▁proportional ▁to ▁the ▁magn ifying ▁power . ▁It ▁is ▁usually ▁not ated ▁in ▁a ▁linear ▁value , ▁such ▁as ▁how ▁many ▁feet ▁( met ers ) ▁in ▁width ▁will ▁be ▁seen ▁at ▁ 1 , 0 0 0 ▁yards ▁( or ▁ 1 , 0 0 0 ▁m ), ▁or ▁in ▁an ▁angular ▁value ▁of ▁how ▁many ▁degrees ▁can