ism ▁sets ▁to ▁guarantee ▁they ▁don ' t ▁lose ▁their ▁reflect ive ▁qual ities ▁if ▁they ▁get ▁wet . ▁ ▁One ▁variant ▁form ▁was ▁called ▁" tr en ch ▁bin oc ular s ", ▁a ▁combination ▁of ▁bin oc ular s ▁and ▁per is cope , ▁often ▁used ▁for ▁art illery ▁spot ting ▁purposes . ▁It ▁project ed ▁only ▁a ▁few ▁inches ▁above ▁the ▁par ap et , ▁thus ▁keeping ▁the ▁vie wer ' s ▁head ▁safely ▁in ▁the ▁tren ch . ▁ ▁Military ▁bin oc ular s ▁of ▁the ▁Cold ▁War ▁era ▁were ▁sometimes ▁fitted ▁with ▁pass ive ▁sens ors ▁that ▁detected ▁active ▁IR ▁em issions , ▁while ▁modern ▁ones ▁usually ▁are ▁fitted ▁with ▁filters ▁blocking ▁las er ▁be ams ▁used ▁as ▁weapons . ▁Further , ▁bin oc ular s ▁designed ▁for ▁military ▁usage ▁may ▁include ▁a ▁stad iam et ric ▁ret icle ▁in ▁one ▁oc ular ▁in ▁order ▁to ▁facil itate ▁range ▁estimation . ▁ ▁There ▁are ▁bin oc ular s ▁designed ▁specifically ▁for ▁civil ian ▁and ▁military ▁use ▁at ▁sea . ▁Hand ▁held ▁models ▁will ▁be ▁ 5 × ▁to ▁ 7 × ▁but ▁with ▁very ▁large ▁pr ism ▁sets ▁combined ▁with ▁e y ep ie ces ▁designed ▁to ▁give ▁gener ous ▁eye ▁relief . ▁This ▁optical ▁combination ▁prevents ▁the ▁image ▁v ign et ting ▁or ▁going ▁dark ▁when ▁the ▁bin oc ular s ▁are ▁pitch ing ▁and ▁v ibr ating ▁relative ▁to ▁the ▁vie wer ' s ▁eye . ▁Lar ge , ▁high - m agn ification ▁models ▁with