I use B+W exclusively for circular polarizers , preferring the B&W Käsemann with Nano coating both in the standard and slim versions.
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. B+W filters are manufactured by Schneider Optics. Each filter is cut from raw cylinders of pure Schott optical glass, producing the flattest possible filters. This precision flatness (plano-parallelism) and high-quality anti-reflection coating, which is applied to both sides of the filter, minimizes the possibility of image deterioration due to flare. The filter mounts are made of solid brass, which are then black anodized, which is preferable and more durable then other coatings. It should be noted, other top lens and filter manufacturers use similar high quality precision components and coating technology. So there are more then a few from C-PL\'s other vendors that are equally very highly rated.
