This will be a somewhat windy explanation with a couple of questions at the end. I have been having problems with edge to edge sharpness in my prints and after following the good advice in other threads regarding enlarger alignment, I brought my Beseler 23C up to code, so to speak. But I still can't get the negatives focused all the way around: the center will be sharp but the left side will be slightly out of focus and the right side a bit more. I did battle with it tonight for about two hours using a bit of film leader with a grid scratched into it, and no amount of adjusting will get all quadrants into focus - the center still gets very sharp, but even when I get the edges close they still don't get as sharp as the center. I've tried shifting the lensboard to see if the soft areas change, but they stay constant. Again, I've already checked to make sure the different planes are parallel.
I use 35mm and 6X4.5 and 6X6 formats, and have verified that the negatives I have been trying to print are indeed sharp from edge to edge.
So I've come up with two possible solutions I wanted to get advice on, and please feel free to offer more. Number 1: my lenses are probably entry-level, hobbyist quality. Would higher quality enlarger optics make a substantial, easy to see difference in the edge to edge sharpness? Number 2: I'm using the basic negative holders. Would glass holders (assuming they make them for the 23C) make a noticeable difference by virtue of the fact that they hold the negatives flatter?
Thanks in advance.