Light rays which are reflected by any surface become polarised & polarising filters are used to select which light rays enter your camara lens. PL (Linear Polarising) & PL-CIR (Circular Polarising) filters have the same effect, but it is important that you choose the correct version for your camera. They allow you to remove unwanted reflections from non-metallic surfaces such as water, glass etc. They also enable colors to become more saturated & appear clearer, with better contrast. This effect is often used to increase the contrast & saturation in blue skies & white clouds. HOYA's polarising filters do not affect the overall color balance of a shot. Light rays which are reflected by any surface become polarised & polarising filters are used to select which light rays enter your camara lens. PL (Linear Polarising) & PL-CIR (Circular Polarising) filters have the same effect, but it is important that you choose the correct version for your camera. They allow you to remove unwanted reflections from non-metallic surfaces such as water, glass etc. They also enable colors to become more saturated & appear clearer, with better contrast. This effect is often used to increase the contrast & saturation in blue skies & white clouds. HOYA's polarising filters do not affect the overall color balance of a shot. How to select the correct Polarising filter: Many of today's cameras use semi-silvered mirrors or prisms to split the light entering the viewfinder in order to calculate exposure & 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 filter unless you have a manual focus camera which has no beam splitter.