Quote Originally Posted by ian_greant
Here is one I've read about but haven't done yet (even though my enlarger is slightly out of alignment)

1) expose a negative on a blank wall, grey card, what ever. and process it
2) scratch a small "x" in each corner of the negative
3) put it in the appropriate negative carrier and in the enlarger (duh)
4) Check focus in each corner and adjust until all are equally in focus.

I use this method, although I just pick a "junk" neg to scratch, and check the focus with my grain magnifier.