Shootout: Leica 90mm f/2.4 Summarit-M vs Leica 90mm f/2 APO-Summicron-R ASPH (Green Lichen Barn Exterior)
In Guide to Leica, this comparison answers a practical question: in what ways is it worth spending for the slightly faster APO 90mm?
The question is answered unequivocally.
The Leica 90mm f/2 APO-Summicron-R ASPH was used, which is optically identical to the Leica 90mm f/2 APO-Summicron-M ASPH. The R version has the advantage of being directly usable on Leica M or Canon with a lens adapter, or convertible to Nikon mount, and I prefer its ergonomics over the M version.