Are there any real-world benefits, optically, of the B+W XS-Pro over the F-Pro? I'm after a UV protection filter, but don't want to unduly compromise the optical performance of my lens. XS has a brass interface, the F-Pro an alloy (an aluminium alloy I suppose). The XS is thinner too, but I'm mainly interested in the optical performance. I guess there's very little in it, apart from some extra bucks flying out of my pocket (yes we use the monetary term bucks over here too ).