But all Leica lenses, even the Noctilux, are sharper stopped down a bit, f/4 usually. So your 'investment' is in an additional stop or two of speed, not resolution. You are wasting the prime performance of the lens for the sake of using a narrow definition of its function. Leica designed it with a selection of f/stops, that is why it is expensive, a lens with one f/stop would be pretty cheap to make in the scheme of things.I try to shoot each of my Leica lenses wide open almost all the time. Leica (and I) spent a great deal of money making sure these lenses perform better than any alternatives when wide open, and I don't want to waste that investment.
Steve