B+W Polarizers increase color saturation and reduce reflections, circular polarization has the same pictorial effect as linear polarization, but allows for proper exposure metering and/or autofocus distance settings with modern automatic cameras.
The individually selected “high-end” polarizing foils of the Käsemann-type filters are neutral in color, have a higher efficiency than conventional polarizing foils. They are cemented between high-grade plano-parallel optical glass, the resulting sandwich is then precision-polished again to achieve highly accurate plano-parallel surfaces. Subsequently they are edge-sealed to protect the foil against humidity and extremes of temperature. Brass mounts made on CNC-controlled machines ensure precise seating on the lens.
There’s no point in buying an expensive, optically superior lens, only to put a piece of inferior glass over the front of it! B+W filters all feature brass mounts, designed to fix the high-quality filter glass in position “for life”. Brass mounts won’t bind with your lens thread, or other filters – a major advantage over cheaper filters.