Heliopan 52mm Linear Polarizer Filter (705239) Removes Reflections And Increases Color Saturation Without Affecting The Overall Color Balance Brass Is Used To Make Most Of The Rings For The Filters And Adapter Rings. Aluminum Is Used For The Rigid Lens Hoods Like The telephoto Metal Lens Shades. For The Rubber Lens Hoods A Special Rubber Mixture Is Used Filter Factor: Between 2.3 And 2.8 (Approx. +1.3 Stops) For brilliant color reproduction, best contrast and sharpness Heliopan offers the highest quality optical glass from the German Schott Group. High quality hard coating on each filter side to reduce stray light, to maintain high contrast and avoid flare Minimal reflections because of matte black anodized brass filter rims which will not bind when threaded in combination with other metals. Limited Lifetime Warranty