APUG'er john_s from down under has been so kind to provide me with the data missing from the Rodenstock pdf available online. Thanks a lot John.
From these figures (see below) it is clear that stopped down (f/5.6) and at moderate enlargement (10x) there will be no discernible difference between the regular Rodagon 50mm f/2.8 and the Apo-N version. No surprises there then. It's what most people see in practice as well.
If anything, at f/5.6 & 10x, the Apo-N is actually slightly (slightly) 'worse' (i.e. lower MTF) in the very centre of the image, and also has a bit more distortion. Not that anybody will be able notice, but still interesting to see how good the regular 50 Rodagon really is. Who needs an APO?
Obviously the Apo-N is all about wide-open performance. Maybe it's also better at larger magnifications, but then for the 20x range Rodenstock have a dedicated lens series (Rodagon-G) that will best both these Rodagons.
Anybody willing to trade their regular for my Apo-N?