The Tiffen 4 x 4" Ultra Warm Polarising filter is a remarkable filter designed to bring much more "punch" to your images. If a traditional polariser doesn't give you enough "pep", the "Ultra" polariser offers you a little more. It will further enhance your blue skies - making the difference between a good photograph and an exceptional image. The extra warmth this filter generates comes from incorporating Tiffen's exclusive 812 warming filter.nnReflected light rays become polarised. Polarising filters are used to select which light rays enter your camera 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 seen through the viewfinder and modified by rotating the filter. The filter factor varies depending on the filter's rotation and its orientation to the sun.nnNote: Linear polarisers are used with most video cameras and manual focus cameras. They are not recommended for autofocus SLR cameras. Circular polarisers are specifically designed for use with autofocus SLR cameras (they will also work on manual systems and video cameras without problems).nnnFeatures:nn- Your deep blue sky will become even more "blue"nn- A highly efficient designnn- Adds warmth to the imagenn- Made from White Water glassnnnSpecifications:nn- Type: Ultra Warm Polarisernn- Size: 4x4" (101.6 x 101.6mm / 4mm thick)nn- Filter factor: Between 2.3 and 2.8 (approximately +1.3 f-stops) - approximatelynn- Effect: Eliminates reflections and increases colour saturation without affecting overall colour balance; Adds warmth to the imagenn- Application: Nature, travel, outdoor photographynn- Colour temperature: No changenn- Construction: White water glass