I'm thinking about picking one up with a 50mm f/2 for a nice travel/walkaround. There is one at a local shop and the price isn't bad. Anyone have any experience with the R4 or the 50mm f/2 Summicron R? I'll also grab an adapter for the 50mm for use on my 5D. Is the lens truly the same optically as the 50mm f/2 Summicron M?