WYATT 72mm Pro 1 Digital Circular Polarizer Filter, Slim 3.06mm with High Definition Multi-Resistant Nano Coating CPL Super-thin thickness of 3.06mm, applicable to more wide-angle lens, HD light transmittance of 98%. Germany optical glass, top level of transmittance. Reduce the non-metallic surfaces reflect light to improve picture quality This polarizing filter is used to increase color saturation,darken blue skies so white clouds stand out and eliminate reflections from nonmetallic surfaces like glass or water It will also reduce the softness in scenery caused by atmospheric haze,this filter will not change the overall color balance of a photograph Most modem SLR cameras use a polarizing half mirror(split beam metering)system and the Circular PL is designed to be used with them Filter Factor:3~4 or 12/3 to 2 stops