The Tiffen 4 x 5.65" Ultra Warm Linear Polarising Filter in ColorCore glass is a remarkable filter designed to bring much more "punch" to your images. If a traditional polariser doesn't give you enough "punch", the "Ultra" polariser offers you a little more. It will accentuate your blue skies even further - making the difference between a good photograph and an exceptional image. The extra warmth that this filter generates comes from the incorporation of Tiffen's exclusive 812 warming filter. Reflected light rays become polarised. Polarising filters are used to select which light rays enter your lens. They can eliminate unwanted reflections from non-metallic surfaces such as water or glass and also saturate colours, providing better contrast. The effect can be observed through the viewfinder and modified by rotating the filter. The filter factor varies depending on the rotation of the filter and its orientation relative to the sun. Note: Linear polarisers are used with most video cameras and manual focus cameras. They are not recommended for autofocus reflex cameras. Circular polarisers are specifically designed for use with autofocus reflex cameras (they will also work without problems on manual systems and video cameras). - Your deep blue sky will become even "more blue" - A highly efficient design - Adds warmth to the image ColorCore Technology - Tiffen filters are manufactured using ColorCore technology, a closely guarded exclusive process that involves permanently laminating the filter material between two pieces of optically flat polished glass with tolerances of one ten-thousandth of an inch, then mounting them in precision metal rings - The ColorCore process allows Tiffen to control the colour and density of their filters, as well as the characteristics of special effects filters with precision far superior to typical dyed-in-the-mass filters, which typically exhibit variations in colour and density. Superior Quality - The major Hollywood film studios trust Tiffen filters for their multi-million pound productions - The superior quality and design make Tiffen the undisputed choice of filmmakers, professional photographers and even NASA - Tiffen has also received an Emmy from the Academy of Television Arts and Sciences for excellence in engineering Specifications