The Pro1 filters have better coatings and are also thinner - less likely to cause vignetting - but far more expensive than the standard ones. I'm not sure what the technical differences are between HMC and DMC but if I were cynical
I'd say that the 'digitally optimised' bandwagon is gathering speed.
Hoya do two ranges as well as the Pro1 - green box (cheaper) and blue box (multicoated).
And then there's the school of thought which says that the last thing you should do with a nice, expensive lens is to put a piece of superfluous glass on the front of it, which will increase the risk of flare. The argument goes that the best protection is a lens hood, and if you bash a filter on something it may break and the glass fragments will scratch the lens. But that's a debate that can run and run.
