Used Hollis M-3 Frameless Mask BlackVisibility is the most important aspect of any dive. The new M3 mask provides that with distortion free vision and superior fit. This low profile design uses a rigid frame and two lenses with 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