Hoya 37mm HD2 Protector, 8-layer Multi-Coated Glass Filter The Hoya HD2 Protector is the ultimate in clear filters. It has no effect on sharpness, color balance or performance of the lens in any way. Keeping on the lens constantly will protect the front element of the lens from damage due to dirt, sand, spray or knocks and scratches." HD Glass - High Density Sharp Cut Glass Chemically Enhanced Optical Glass is 4x Stronger than Normal Glass HD Coating - 8 Layer Anti-Reflective Multi-Coating Water & Oil Repellent Top Coating is Oil and Stain Resistant for Easy Cleaning HD Frame - Wide Angle Lens Compatible Ultra Thin Aluminum Frame Glass Mounted with High Pressure Press Technology, No Retaining Rings