Hmmm, on centre, maybe, but when you take overall performance into account (corners included), wide open is rarely the best aperture. Wide open works better with longer lenses with more coverage and when making small enlargements. Try making a 20x16 from a 35mm neg on a 50mm non-APO Nikkor/Rod/Schn at f2.8 and the resultant print will be dramatically worse than at two or three stops down. Not only will the corners be poor, but falloff will be more of an issue too.
I dont own any APO lenses, but I understand they are optimise for a stop of so down from wide open, whereas other lenses generally give best performance 2-3 stops down.
While best resolution may occur on centre wide open with many lenses, the improvement in resolution would not justify the reduction in performance in other areas in my experience. Where I have compared sharpness of enlarger lenses on centre at various apertures, the differences have been trivial and not worth considering. The corners, well, thats another matter!
Originally Posted by frotog