Tired of not being able to see well underwater? Can't read your computer or gauges? Maybe you not sure what F-Stop you are setting your camera on? If these are problems for you when diving you need to get a set of Diopter lenses for your dive mask. See things clear underwater with this Cressi Negative Diopter for your Cressi Focus Mask. Easy to install and WOW! You can now see everything better than before. Lenses are available from -1.0 to -10.0 in 0.5 Diopter increments for left or right side lens.