Eyepieces

Many modern binoculars, in particular roof prism binoculars, are nitrogen-purged. These are watertight instruments. To prevent fogging from the inside, the binoculars are filled with molecular nitrogen. The instruments are thereby equipped to withstand large temperature fluctuations.

So-called IP codes indicate the level of waterproofing, and also the protection against the ingress of dirt or other foreign material such as sand.

If the device is waterproof it will have been tested in line with codes IPX5, IPX6, IPX7 and IPX8: the designation IPX5 may be used for devices if they can withstand water projected from a nozzle from any angle. IPX6 in turn refers to powerful water spray, IPX7 temporary immersion, and IPX8 continuous immersion.
Above all, the latter two ratings are therefore important for all binoculars and devices designed for sailing, fishing or situations of severe temperature fluctuations, and similar applications.