I just got back from a low light project shooting an autofocus Nikon SLR and a Bessa R4. It was not too dim, but I was using slow wide lenses and EI 200 with flash. (Non-flash reading with the Bessa was f4 at 1/8). I can't say one is better than the other in terms of low light focus, they both have advantages and disadvantages. I was using wide angle lenses (35mm and 21mm) and near the end of the night I had pretty much reverted back to zone focus for both cameras.