Heliopan Bayonet 3 Linear Polarizer Filter.

Light rays which are reflected by any surface become polarised and polarising filters are used to select which light rays enter your camara 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.