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 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. 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.
For this high-end polarizing filter the foil pieces are selected individually for maximum color neutrality. Following cementing between highgrade optical glass, additional grinding and polishing takes place. This guarantees outstanding sharpness even with very bright, apochromatic lenses. The latest cementing technique ensures lasting stability even in damp climates.
The acronym "MRC" stands for "Multi Resistant Coating". The lens coating normally used for B+W photographic filters and certain SCHNEIDER lenses is resistant in several respects: for one thing, to the influence of dust and moisture, for another, it offers a significantly higher resistance to mechanical scratches on the surface of the lens. The cleaning of filters with this hard, water-repellant system of coatings has become altogether considerably easier. The broad-band anti-reflection coating MRC is produced by a plasma-supported condensation-deposit process. In this process, the accelerated inert-gas ions condense the material deposited as very compact and resistant layers. The uppermost layer consists of fluorinated Siloxan. Each side of the filter consists of a system of eight interference layers, i.e., sixteen layers per filter in all, with a total thickness of about 250 nm! This corresponds to a thickness of ¼ µm! The uppermost layer has low surface energy, which is to say low surface tension; this results in a high wetting angle of contact, e.g., against water, of about 120°. This phenomenon is similar to a drop of mercury on a piece of glass. It is in this low surface tension that the physical secret lies, namely, why the new MRC coating considerably inhibits the adhesion of moisture.
The B+W standard filter mount F-Pro provides some substantial enhancements over the previous B+W standard mount. It has been given a shallower design while maintaining the excellent material and production quality and its unchanged high mechanical stability and can therefore now also be used without any risk of vignetting for many wide-angle lenses. While no exact focal length limit can be given, since the vignetting depends not only on the height of the filter mount, but also on the tube design of the lens, it can generally be considered that the B+W standard filter mount F-Pro can be used without any vignetting with 35 mm film, and indeed always up to 35 mm, almost always at 28 mm and frequently even at 24 mm focal length. Focal lengths on digital will be lower depending on the sensor size or conversion factor. Another advantage of the new F-Pro mount is that the screw ring which holds the filter glass in the mount is no longer inserted from the front, but from the rear. This means that the screw ring can no longer be loosened unintentionally after an additional filter or a lens hood has been screwed on (too tightly) and then unscrewed again.
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