The important role played by the filter mount and its mechanically complex task are often underestimated. Although mounts are supposed to fix the high-quality filter glass in position “for life”, they must not cause any sharpness-reducing tension in the glass. B+W manufactures various mount types, mainly out of stable brass, on CNC machines. The filter glass is screwed into a highprecision retaining ring, applying a pre-specified torque. Besides the excellent F-Pro standard mount which is suitable for telephoto lenses up to the most common wide-angle focal lengths, B+W offers the very flat XS-Pro mount for super-wide-angle lenses. This eliminates vignetting. For even more extreme focal lengths there is the oversized mount on which the filter glass protrudes far beyond the thread of the retaining ring (more under “Filter mounts”). It is the high-grade mounts that finally make a B+W filter a true piece of high-tech that you can rely on for many years to come.