Uselessdreamer1's post reminded me of a question I've been meaning to ask for a while. Does anyone know what the differences between the following lenses are, if any? MD Rokkor-X 50mm 1:1.7 MD Rokkor 50mm 1:1.7 MC Rokkor-PF 50mm 1:1.7 MC Rokkor-X PF 50mm 1:1.7 I know the difference between an MD and a MC, but what does X mean? I assume it means it's the higher end lens? The one for professionals? I think the PF has something to do with the number of elements, but can't remember. I can't find a site that tells me either. :?