Circular polarising filters (CPL) help reduce unwanted reflections in non-metallic surfaces such as water and glass. It helps to boost contrast and colour saturation by filtering out light which has become polarised by reflection. This also helps increase contrast between blue sky and cloud as well as plant foliage. The circular polarisation is created by the addition of a quarter-wave film to the standard polarising film and this makes it ideal for use with all cameras, especially those with autofocus and complex exposure measurement systems.