I'm new here, so be gentle...
Hope it's not too late to add to this debate but I've been looking at the lenstip.com test that so many people refer to and find myself drawn to the B+W filters simply because of the almost complete lack of additional flare around the lamps in the test photos, which is very evident with the winning Marumi - green flying saucers. This seems more noticeable than any other factor that would affect my choice and is fairly consistent across their range which leads to the cheaper C-POL MRC, non-slim [no annoying lens cap problems] non-KSM [simply for cost, as it's going on a pretty cheap lens anyway, though it does show even less flare than its cheaper sibling.] Have I got my priorties all wrong? Even this cheapest B+W has a brass mount - though some websites say it doesn't? - and the hard, protective coating, and apparently doesn't fall apart as regularly as the Hoya HD, which was my initial instinctive choice, all of which sound like plus points. Perhaps it's too good for my kit - many of you have equipment I could only dream of - but I hope I'll only ever buy the one. As it's only 55mm it's not too pricey, just a couple of quid more than the Marumi though quite a bit more than the Hoya HD. Does anyone out there think this is a reasonable conclusion?
One further query; some of the transmission plots for these filters, including Hoya's own, show that they start cutting well inside the visible part of the spectrum, which I believe starts at about 370-380nm. The Hoya HD's plot is down to virtually 0% by then having started falling at about 450nm, well into the blue, meaning, surely, that any violets, purples, dark blues and so on will be dramatically darkened. Doesn't this cause problems, or is this end of the spectrum somehow unimportant? If I tried to photograph Deep Purple in concert, would they disappear? Just kidding, but how can it be right to cut out so much of that end of the spectrum, or have I got it all wrong again?
Cheers.