It happens to any lens collector at some point: how often will a polarizing filter be attached to a particular lens? Few lens suppliers spend energy on 'standardizing' their filter threads, but polarizers are expensive - so when to say when?
In my case I'm trying to stop at two: the 58mm and 67mm sizes that fit my 16-45 and 55-300 Pentax lenses. I have a 55 and 72 from my Alpha days though, but would prefer not to carry so many! I picked up the big set of step-up rings (eight, I think); my 50mm lens now has 52-55-58 (2 rings) which not only adapt the filter, it makes for a decent though shallow hood! I can take the 55-58 plus filter for my 135mm, and the 67mm size fits my Rikenon 28-100 just fine. Problem with that one is that it's a really heavy lens at 605g, I fear it's not long for my bag as it's over my personal weight limit.
I'm seeking a 'tweener zoom to bridge the 16-45 and 55-200, as the 50 is great but at times a bit of zoom would improve composition. Something in the range of that 28-100 is good, but smaller would be more used - I've sought in vain for a Sigma 28-80 f/2.8-4 (and its 58mm thread size!). In the meantime I've bid on a 28-135 Sigma that could go with me on many unscripted walks when 16 won't be needed and 300 is too large; we'll see if that bid wins in a day or so. I had hoped that 16-45, 50, 55-300 would be 'perfect' for me, but of course I'm not perfect so why should I expect it elsewhere? :^)
