Marine binoculars area of use golf bird watching travel nature watersports magnification 7 x lens diameter 50 mm prism system porro exit pupil diameter 714 mm min focus distance 6 m angle of view 63 field of view in 1000 m 110 m twilight factor 187 relative brightness 50 98 focussing system central focus viewing straight binocular weight 1 000 g outdoor function waterproof