Creates dramatic sky/cloud contrast. Saturates colors without changing color balance. Mount rotates to control amount of effect. Light rays which are reflected by any surface become polarised and polarising filters are used to select which light rays enter your camera lens. They allow you to remove unwanted reflections from non-metallic surfaces such as water, glass etc. They also saturate colors and increase contrast. Polarizers come in two variations but have the same effect. Linear polarizers work with older camera meters; Circurlar polarizers are designed for today's newwer slpit-beam metering systems used in auto focus cameras. Check your camera's manual.