These filters offer both amateur and professional photographers HOYA's famous quality at reasonable prices. They have coatings applied to both surfaces to suppress reflection and increase light transmission. 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.
Many of today's cameras use semi-silvered mirrors or prisms to split the light entering the viewfinder in order to calculate exposure and focusing distance. PL (Linear Polarising) filters can sometimes interact with these items to give unpredictable exposure or focusing. So we recommend that you choose a PL-CIR (Circular Polarising) filter unless you have a manual focus camera which has no beam splitter.