Waterproof binoculars

Dust-, waterproof

— the housing, protected from dust and moisture, allows the binoculars / monocular to endure difficult external conditions — rain, fog, dusty wind, etc. without consequences. Note that not all such devices are completely sealed, but anyway they are better suited for use in nature away from shelters than conventional ones. And the most advanced dust and moisture-proof models are able to withstand even complete immersion in water; an indicator of such possibilities is usually gas filling (see the relevant paragraph).