Hoya engineers recognized a need for a circular polarizer filter that could meets the demands of super high resolution cameras, and the needs of photographers who shoot in conditions where every bit of light is important. Utilizing a new multi-coating process that applies 16-layers of anti-reflective coating to the optical UV glass, Hoya created a filter that is 2x sharper and a coating that is 200% harder than the award winning HD2 circular polarizer filter.In addition to being extremely scratch and abrasion resistant, this hardened coating is stain resistant and easy to clean when oil and smudges like fingerprints are introduced to the surface. Hoya selected a premium high transmission polarizing film the yields greater light transmission than standard PL films - an additional 2/3rds of a stop of light passing through the filter for a total light loss of 1 stop. The HD3 Polarizing glass is housed in a two-piece, lightweight, low-profile, aircraft grade aluminum filter frame. This two-piece design allows the filter to maintain perfect parallel alignment to the sensor plane for maximum sharpness and zero distortion. Knurled edges on both rings allow for easy rotation to achieve the desired polarizing effect, and easy attachment and removal from the lens. The low-profile design eliminates the concern for vignetting when used on ultra-wide-angle lenses, and the front filter threads accepts lens caps and other filters for stacking. Circular polarizing filters allow photographers to achieve creative, in-camera, effects not possible after the image is created. A polarizing filter simply filters out unwanted reflections from non-metallic surfaces such as water and glass in addition to light reflecting off moisture and pollution in the atmosphere. This results in bluer skies, greener leaves, reduced or eliminated reflections, and greater clarity in your final image.