I have an elderly Meopta enlarger (Opemus 4). I've put quite a lot of effort into aligning this beastie, and to the best of my knowledge the neg carrier, lens and baseboard are parralel to each other, left to right and front to back. (Using a spirit level) I'm currently using this for 35mm only.

One test I do is to use an old fim leader into which I've scratched a grid, and focus this onto the baseboard. What I'm seeing now is that I can get the center and left in focus, but not the right hand side. I can't seem to be able to adjust this out either. I can make it worse but not better.

Does anyone have any suggestions as to what may be causing this and possible solutions. (Other than buying another enlarger! I hate being beaten by a bit of metal and glass.)

If it's relevent I'm using a Nikkor 50mm f2.8 lens.