The NiSi 77mm Nano Coating Graduated Neutral Density Filter GND16 1.2 Nano coated optical gradient filter is made from environmental optical glass (H-K9L). The glass is annealing environmental protection optical glass H-K9L. Double sides optical grinding and polishing to make sure the optical high parallelism and smooth which ensure the high sharpness of image. Neutral density filter coated on double sides via 200C high temperature coating. The spectrum curves and straight and flat. It’s soft transition from visible light to infrared light. There is anti-electrostatic coating can resit dust and also can endure wipe off organic solvent. AR and water-proof coating on double sides make the filter won’t fade after several years.