Light rays that are reflected by any surface become polarised and polarising filters are used to select which light rays enter your camera lens the filter factor is between 23 and 28 approx 13 stops this varies in accordance to how the filter is orientated to the sun or rotated both the pl linear polarising and pl cir circular polarising filters have the same effect however it is important that the correct version is chosen for your camera the hoya 72mm linear polaris