This is the Apollo Bio-Metal Aluminum Frame Low Profile Scuba Diving Mask Features: Apollo's Bio-Metal offers the largest field of vision Using aluminum allows the Bio-Metal frame to be produced with a very low profile while still supporting a twin lens design Twin lens design is preferable to single because it brings each lens closer to the eye for a wider field of vision and reduced inner volume Aluminum also allows for a very minimal center pillar. The slim-line center pillar is narrow enough to have almost zero effect on field of vision Divers often feel a slight distortion of view. Cause: lack of alignment between the lens and actual eye center Lenses are ground like a sphere to provide optimum efficiency at the center of the lens. The lens center is designed to more naturally match that of your eye The Bio-Metal mask provides superb clarity and 180° field of vision Comfort is just as important as vision. The high quality surgical silicone flange is soft and designed to collapse accordion style, eliminating stress points on the delicate facial area. Built-in drainage channels allow a diver to clear without lifting off the face. Just look up and exhale lightly through the nose.