Originally Posted by
neuroanatomist
Normal is just that, except that there are actually two flavors of normal - one will have the MRC designation (multi-resistant coating), which is a multilayer coating that reduces reflections and is easier to clean. If there's no MRC in the name, it's just got a single layer coating. MRC is better (and more expensive).
Käsemann filters are the higher grade of CPL. Here's what B+W says about them: "This high quality polarizer is crafted from select polarizer foils and specially prepared optical glass. This neutral polarizer is edge sealed and therefore, it is durable under extreme climatic conditions." Käsemann filters are always MRC coated. Personally, I have Käsemann CPLs in both 77mm and 82mm sizes, in the Slim mount.
The Käsemann EW (or any B+W filter with an EW designation) is 'extra wide' meaning it's designed for ultrawide lenses. Basically, the glass is one size larger, and the filter combines a step-up ring in the mount. For example, a 77mm EW filter has 82mm diameter glass pieces but threads onto a 77mm filter thread - the larger glass means less chance of vignetting commonly seen on UWA lenses (where, to be honest, using polarizers is challenging due to uneven polarization at FF-equivalent 24mm and wider). Other options to redude vignetting are the Slim mount (thinnest option, lacks front threads) and the XS-Pro mount (still slim, but a little thicker and retains front threads for a lens cap).
Hope that helps...
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