x-ray
Veteran
In reality there is only 1/3 stop difference and the DOF is more influenced by the focal length 40 vs 50mm than 1/3 f stop. I had the Noctilux 1.2 for a number of years and found its performance wasn't very good stopped down past f4 in comparison to my summicron.
http://www.photo.net/photos/X-Ray
http://www.photo.net/photos/X-Ray