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. Filter factor is between 2.3 and 2.8 (approx. +1.3 stops).
This unique filter is the result of a collaboration between Hoya and respected wildlife photographer, B. Moose Peterson. It combines the advantages of a polariser with the warming effect of an 81A filter.
Circular polarisers are specifically designed for use with auto-focus SLR cameras (They will also work on manual systems without problems).