Product Description Circular polarizing filters are made for all cameras with beam splitters in the light paths of their TTL exposure meter and with autofocus lenses. Circular polarization has the same pictorial effect as linear polarization, but allows for proper exposure metering and/or autofocus distance settings. The "high-end" polarizing foils of the Käsemann-type filters are neutral in color, they have a higher efficiency than conventional polarizing foils and they are cemented between high-grade plane-parallel optical glass. The resulting sandwich is then precision-polished again to achieve highly accurate plane-parallel surfaces. Subsequently they are edge-sealed to protect the foil against humidity. Discriminating photographers regard the B+W Käsemann-Type Polarizing Filter to be the very best of all polarizing filters. They are well suited for applications that require the highest possible imaging quality, especially with high-speed telephoto lenses and apochromatic lenses. From the Manufacturer Käsemann Circular Polarizers - The Highest Quality Polarizer Available The images on the left was taken without any filter. The image on the right was taken using a B+W Circular Polarizer. The images on the left was taken without any filter. The image on the right was taken using a B+W Circular Polarizer. Circular polarizing filters are made for all cameras with beam splitters in the light paths of their TTL exposure meter and with autofocus lenses. Circular polarization has the same pictorial effect as linear polarization, but allows for proper exposure metering and/or autofocus distance settings. Käsemann polarizing foils are neutral in color, have a higher efficiency than conventional polarizing foils, and are cemented between high-grade plano-parallel optical glass, using a special cementing technique that resists delamination in humid climates. The resulting sandwich is then precision-polished again to achieve highly accurate plano-parallel surfaces. Discriminating photographers regard the B+W Käsemann Polarizer as the very best polarizer on the market. They are well suited for applications that require the highest possible imaging quality, especially with high-speed telephoto lenses and apochromatic lenses. B+W Polarizers increase color saturation and reduce reflections. The filter factor varies according to how the filter is positioned in relation to the sun. Exposure compensation is about two f-stops. Why Use a Circular Polarizer? Modern DSLR cameras have a beam-splitting prism that sends part of the incoming light to the meter and part to the viewfinder. The effect is that the light entering the meter is partially polarized by the beam-splitter. A linear polarizer placed on the lens of such a system will act as a second polarizer and block light to the meter by a degree dependent on the angle between the prism and the polarizer on the lens. The result is incorrect exposure/aperture values from the meter. That's why you need a circular polarizer with such cameras. The circular polarizer circumvents this problem by adding of a 1/4-wave retarder, or delay foil. This ensures that the linearly polarized light is changed into a rotation that appears unpolarized to the meter, resulting in proper exposure/aperture readings. B+W's Superior MRC Coating with Nano Technology Illustration of lotus effect on water droplet caused by nano coating. The nano coating is an outer layer of protection that comes standard with all XS-Pro Digital MRC filters. The nanotechnology based characteristic (lotus effect) produces a better beading effect with water, making the cleaning of this filter even simpler and faster than ever before. MRC nano has an improved outer (8th) layer over regular MRC. The lens elements of high-quality lenses and the plano surfaces of filters require a perfect shape and smoothness to achieve the best optical quality. Dirt, greasy fingerprints, water marks and scratches reduce the image contrast and the sharpness, whi