Different Types of Masks Used in Diving
Given that the human eye evolved for seeing on land, attempting to see underwater while scuba diving can prove hard. Even without the added problem of chemicals in the water that irritate eyes, the water itself can pose problems. First, with its higher density, water has a different index of refraction from air and makes things look bigger and nearer. On top of this, water exerts pressure on the eyes, causing their shape to become altered which further distorts one's view. Fortunately, scuba masks can solve these problems. The key is knowing the different types of masks and what the advantages of each is.
Swimming goggles are used primarily for swimming near the surface, often in competitions. As a result, they only cover the eyes to keep out chlorinated water and prevent splashing water or momentary submergence from distracting the swimmer's vision. At the same time, their small size and separate lenses allow them to hug the face and provide a streamlined profile. They're not meant for diving to any significant depth as they contact the wearer around each eye socket and would be painfully forced into the sockets with enough pressure.
Diving masks have general design features to handle underwater pressures when engaged in things like scuba diving in Key West. They have a seal rim called a skirt that contacts a large area of the face to reduce pressure in any particular spot. They should preferably have a flexible nose cover, too. This keeps water out of the nose, lets the diver pinch their nose to clear their ear canals, and to allow air from their nostrils to force water out of the mask itself. The best way to check that a particular mask will fit a wearer's face is by placing it against the face and drawing air in through the nostrils to see if the vacuum keeps it in place.
The primary feature that's distinguishes different types of scuba masks is the front lens. The shape and position of the lens or lenses greatly determines how a mask can be used.
*Double Lenses: Masks with two separate lenses have gained in popularity mainly because they have less air space within them and require less effort to equalize pressure when descending. An additional advantage to them is that they can accommodate prescription optical lenses for divers with vision problems.
*Single Lens: As the name implies, these masks possess a wide single lens without the divider that interfere with peripheral vision. This type works better for underwater photography when paired with a black skirt that blocks incidental light. With a single open space, they're also easier to use with separate prescription glasses assuming the glasses sit close to the face.
*Full Face: For more serious scuba diving in Key West and elsewhere, full-face masks provide both a wide-angle view and added protection for the face. Also, these masks allow air hoses to be inserted into them instead of being held separately in the diver's mouth.