Hi, Until recently, I've done mostly 35mm photography, but I've been doing more medium format (6x6) recently. I mostly do 8x10-inch and smaller enlargements, but I've done a few 11x14-inch enlargements in the past, all from 35mm negatives. Using a Philips PCS130 enlarger and a Nikon f/2.8 50mm lens, this has produced fine results. Last night, though, I made an 11x14 print from a 6x6 negative, using the PCS130 and an "EL-OMEGAR" 75mm f/3.5 lens. I found that at f/5.6, my enlargement was sharp in the center but very unsharp near the edges. (8x10 and 8x8 enlargements using this lens, mostly at f/8 or f/11, are OK.) I stopped down to f/11, with substantial improvement, although the edges still aren't quite satisfying. The negative carriers I've got are all glassless, so this leaves me with the question: Is the problem the lens (which I bought used on eBay) or the glassless nature of the negative carrier? I don't expect a definitive answer given the information I've provided, but if there are any simple tests or things I could look for to help answer the question, I'd appreciate hearing about them. Also, if my problem is more likely to be the glassless negative carrier, does anybody have any suggestions on how to obtain a suitable insert for my PCS130 negative carrier? My initial thought would be to buy some anti-Newton glass from B&H for another enlarger, ensuring that it's bigger than I need, and have a local glass shop cut it down to size. If there's a better or less expensive approach, though, I'd love to hear it. I've got my eye on a few Schneider Componon, Rodenstock Rodagon, and Fujinon EP 75-80mm lenses on eBay, so getting a (hopefully superior) replacement lens shouldn't be a problem, if the lens is the most likely culprit. Are there any good "sleeper" lenses in this range? Which are the best Nikon models in this range? (I don't know offhand which is their 4- vs. 6-element design in this size.) Of course, I realize that getting both a better lens and glass for flatter negatives is the best approach. I just want to be able to prioritize my purchases. Thanks for any input.