Waterproof binoculars: what waterproof and fogproof mean

What waterproof means to the makers

Celestron defines waterproof equipment as sealed and filled with a dry, inert gas, usually nitrogen, that contains no water vapor. The seal keeps water out. The gas fill handles what is already inside.

Celestron also separates weather-resistant binoculars from waterproof ones. Weather-resistant models have minimal openings that can let water into the optics. Waterproof binoculars go further and are designed to totally exclude water.

If you plan to use binoculars on a boat, the gap between those two words matters. Our marine binoculars list sticks to the makers' own wording for each model.

What nitrogen filling does

Fogproof and waterproof are two jobs. Celestron describes nitrogen filling as an additional barrier to the buildup of internal moisture. Nikon says the gas is effective in preventing fog and mold inside an optical system.

ZEISS makes the same recommendation: it is a good idea to fill the interior with nitrogen or another gas. Dry gas has no water vapor to condense on the lenses when the air outside turns cold.

How the seal is built

ZEISS says only internally focusing binoculars with O-ring seals can be fully watertight. A focus system that moves the barrel parts on the outside has more gaps to seal.

Nikon says its waterproof binoculars keep the body tubes airtight, and nitrogen gas is filled. The airtight body is what holds the gas in, so the seal and the fill work together.

How makers print the rating

Makers print the rating in different ways. Nikon lists the PROSTAFF P7 in 8x30 as waterproof 'Down to 3.3 ft.' with the line 'Nitrogen Filled' and the word fogproof. The listing gives a depth and carries no IP code.

Read the wording on each model's spec sheet. A plain 'waterproof' with no depth and a depth in feet are not the same promise, and a listing that says only weather-resistant matches Celestron's lower tier.

What the rating does not cover

Nikon states that binoculars should not be used underwater. A depth figure such as 3.3 ft describes an accidental dunk, not a dive or a swim with the binoculars in hand.

Waterproof also says nothing about optical quality. The catalog holds 554 models, and 146 of them have ED glass, which is a separate feature from the seal.

Which sizes you will meet most

Sealed binoculars come in every size. The 10x42 is the most common size in the catalog with 87 models, a median weight of 24.9 oz and a median field of view of 336 ft. The 10x42 size has its own figures.

The 8x42 follows with 75 models, a median field of view of 393 ft and an exit pupil of 5.3 mm. Compare the two on 8x42 vs 10x42. For a smaller body, the 8x32 has 28 models at a median 18.5 oz.

Weight and a sealed body

The catalog median weight is 24 oz and the median field of view is 340 ft. The 7x50 is the heavy end of the common sizes at a median 36.8 oz, with an exit pupil of 7.1 mm.

A boat or a wet trail makes sealing the priority, so check the figures for each model on the best binoculars compared list before you settle on a size.