I'm running into a very similar problem with my 45MX right now. I've got an Aristo D2 cold light head, and am using a Schneider Componon-S 135mm lens, and am seeing some vignetting, just about the same as Chuck's example pic. The upper bellows are fully compressed. I took the head off and compared the lighted area of the head to the size of the negative, and there's more than enough area for the negative to be completely illuminated. So it seems like the lens is the culprit. Schneider's site lists both the 135mm and the 150mm Componon-S lenses as covering 9x12 (15cm diagonal), not 4x5 (16.2cm diagonal). Anybody done any coverage comparisons between 135s and 150s for enlarging 4x5?