Thanks again. I just spotted a post on DPReview that says " I'd recommend the clear over a UV though if you're using it as a protection filter, as there is a subtle IQ impact."
I think reading
DPR forum posts has a not-so-subtle negative IQ impact - and in this case IQ does not refer to image quality. Sometimes it's hard to separate the wheat from the chaff over there, to the point where finding the correct facts is like a Where's Waldo hunt.
Case in point, the many people who stated with absolute certainty (to the point of insulting others, also the norm over there) that for B+W filters, MRC = multicoating. For the record, it doesn't - it's the scratch/dirt resisting surface coat; all their MRC filters are also
multicoated, but they do make multicoated filters without the MRC coating.
Any thoughts on Clear vs. UV?
For modern dSLRs, there's no meaningful difference. Note that the references to the contrary in the DPR post are about old CCD-based cameras. I've personally tested my 5DII and found no appreciable sensitivity to 280nm or 350nm light. Yes, there could be some sensitivity just under 400nm, but it's not going to have a significant image impact. Similarly, even the best multicoated filters result in the loss of ~1% of light - a measurable impact, yes, but not a meaningful one.
So, get whichever is cheaper or more available - for B+W, that's usually UV instead of clear, but I've seen some Hoya clear filters cheaper than their UV equivalent.
In terms of quality, the B+W MRC and Hoya S-HMC and higher are optically similar. The B+W is easier to clean, as is the Hoya HD, compared to the other Hoyas. Personally, I have B+W MRC UV filters on all my lenses.
As for an optical impact, there is one - increased susceptibility to flare. That's true with even the best filters (and again, I've personally tested this with the 24-105
and 70-200 II
); low quality filters cause additional problems.