Visibility is the most important aspect of any dive. The M1 mask raises the bar for optical quality and distortion free vision. This lens is an extra clear glass which is valued for its attractive appearance and optical qualities. The low iron content produces a higher light transmittance and a reduced green tint inherent in other glasses. This makes the lens distortion free and helps improve color and visibility in low light conditions underwater.
Just a note on this mask. Do not burn the lens with a lighter to get rid of the manufacturers coating. This weakens the glass and may cause the lens to shatter. This is the only mask that has done this to date.