I pretty exclusively use Hoya Pro1 Digital filters, I know them and know how to affect my lenses, and I have UV, CIR. POL, and ND. Most in 77mm, with a few exceptions.
One thing that I have been "blessed" with is the capability to put fingerprints on my filters, and my post-photography workflow includes a cleaning session of sorts. I use filter pens, the ones with carbon in one end, and a brush in the other end. For the really touch cleaning I have a microfiber/nano-cloth.
However, I find that there is a sort of film that I sometimes end up smearing on the filter, which makes it very hard to get them entirely clean. For these situations, is there a solution anyone can suggest I use? I think the Hoya filters are coated, and I can't help wonder how much this coating can actually take?