Last summer I saw some of Peter's prints while we were at a workshop. And indeed they are sharp. I wonder if the lenses he had trouble with just had focus shift, or more focus shift than other lenses. I have an old 75mm Wollensak that worked fine at all settings. A high end 80mm Rodenstock had shift that made me nuts. Once I recognized this it worked fine when I re-focused when stopped down.

L.G. makes a valid point. I use a old 135mm Schneider with tiny painted on f'/stops and a dot. I keep a small penlight next to the enlarger when working. What a pain.