I know that 80mm f/1.9 on a 645 format isn't actually much different in terms of DOF than a 50mm f/~1.1, but I have to say: I'm always genuinely impressed by how little optical vignetting the Mamiya 80mm f/1.9 has compared to the fast 50mm's for smaller formats. I can understand why people would adapt it to "full frame" and get nearly perfectly round bokeh in the corners.