Full aperture is fine for general focus, not for critical - some lenses have a bit of focus shift between
the widest aperture and the next. Just depends what you are doing too. When I'm doing critical work
like making precision internegs or interpositives with an enlarger, I use only apo process lenses and
check focus with my best grain magnifier, with film in place on a vacuum filmholder. That is often overkill in ordinary black and white printing, but I still tend to do it anyway. My old Scoponet was way
off for any critical work. You can't assume something is properly sized per focal distance just because it is new! Even the double-faced tape used to attach the mirror ruined any precision to the design. Was
fine for casual work, but I'm glad I eventually dropped it on the floor!