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 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. Brass mounts made on CNC-controlled machines ensure precise seating on the lens. Discriminating photographers regard the B+W Ksemann-Type Polarizing Filter to be the
