Hoya HD 49mm CIR-PL circular polariser (CPL) filter. The Hoya HD series are the best filters in the Hoya range. They are high definition, professional filters, manufactured of hardened optical glass to protect them from scratches and damage. Hoya HD CPL's feature special polarizing film, with 25% higher light transmission than standard polarising film used in most lens filters. Specialised coatings are added to the glass to make them water-proof and stain resistant. Various multi coatings further reduce reflections off the surface of the glass for maximum performance. The Hoya polarizer filters allow you to remove unwanted reflections from non-metallic surfaces such as water, glass etc. They also enable colours to become more saturated and appear clearer with better contrast. This effect is often used to increase the contrast and saturation in blue skies and white clouds. Hoyas polarising filters do not affect the overall colour balance of a shot. Suitable for lenses with filter threads of 49mm The Hoya HD range feature hardened glass, with 4x the tensile strength of traditional filters of similar fabrication. This filter is also of great use in today's digital market where sensors are more sensitive to reflected light. Hoya incorporates special coatings that reduce these internal reflections and, thereby, promote a clearer, brighter and sharper image. Light rays which are reflected become polarised. Polarising filters are used to select which light rays enter your camera lens. They can remove unwanted reflections from non-metallic surfaces such as water or glass and also saturate colours providing better contrast. The effect can be seen through the viewfinder and changed by rotating the filter. The filter factor varies according to how the filter is rotated and its orientation to the sun.