From the ManufacturerKäsemann 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 aB+W Circular Polarizer. Click for larger view. The images on the left was taken without any filter.The image on the right was taken using aB+W Circular Polarizer. Click for larger view.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. MRC - A Special Scratch-Resistant, Water and Dirt Repelling Coating The left half of this filter has atraditional coating. The right halfhas MRC coating.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, which can result in blooming at light sources and have an effect similar to a soft-focus lens. A clean front lens element and clean filter surfaces are therefore an absolute pre-requisite for demanding photographers. MRC coating causes waterto bead up and slide right off.The MRC coating is first and foremost a broadband anti-reflection coating. This means that its reflection-reducing effect, which is thus also a transmission-increasing effect, i.e. one which suppresses scattered light and ghost images and transmits more light, has a broadband action over the full spectrum. In contrast, the (almost always blue) single-layer coating only has a high effect in the medium wavelength range around yellow and yellow-green where the eye is most sensitive to light, while its effect is greatly reduced toward the blue-violet and purple-red end regions of the visible spectrum. With the MRC coating, this blue, violet and red to deep-red light cannot produce any contrast reducing scattered light, spotty reflections or ghost images. A broadband effect can only be achieved with a multilayer coating which requires a much higher effort and precision because unevenness and irregularities of the individual layers build up on one another and amplify one another