Blonde Girl With A Diving Mask In The Sea

Use
To prevent a mask from fogging up due to condensation on the glass plate many divers spit into the mask, wipe the spit around the inside of the plate and wash it out with a little water. There are commercial products that can be used as an alternative to the saliva method.
Refraction of light entering the mask makes objects in salt water appear about 34% bigger and 25% nearer when underwater, as shown in the underwater vision article. As the diver descends, the water acts as a colour filter eliminating the red end of the visible spectrum of the sunlight entering the water leaving only the blue end of the spectrum. Depending on the depth and clarity of the water, eventually all sunlight is blocked and the diver has to rely on artificial light sources to see underwater.