Marine binoculars

Nautical

— for use at sea, binoculars must have a sealed waterproof housing (usually such housings are still filled with gas to prevent fogging). At the same time, this is not the only distinguishing feature of marine models: they are equipped with rather large lenses (at least 32 mm in diameter), as well as Porro-type prisms to provide a three-dimensional effect at long distances.