Marine binoculars underwater binoculars area of use bird watching watersports magnification 7 x lens diameter 50 mm prism system porro exit pupil diameter 714 mm min focus distance 7 m angle of view 7 field of view in 1000 m 122 m twilight factor 187 relative brightness 50 98 focussing system individual focus viewing straight binocular weight 1 089 g special features rubber armouring outdoor function waterproof