Quote Originally Posted by jernejk View Post
I will try, but on paper I should actually open it to 5.6 it seems http://www.coinimaging.com/nikon_el50-28n.html
Well, sure, the MTF curves show you that highest resolution of the optics is at some F value. But honestly, the optics resolution is the least of your concerns when printing on the enlarger. The biggest factors that affect print sharpness are enlarger vibrations, head alignment and negative flatness/pop and you have to deal with these before worrying about lens diffraction. At least that was my experience.