Here's a suggested method from Kachel for testing alignment. Use a small format film like 35mm (to reduce film bend issues). Thoroughly fog it and develop it. With a sharp knife, make a clean X mark in the middle and the four corners. Raise the enlarger as much as you can. Focus the center X and make prints of all of them. See if any are out. If all of the corners are out, your lens may not be absolutely flat field (solution - stop down). If they are selectively out, you probably have an alignment problem (possible cheap solution - shims). Hope this helps. DJ(posted 9034 days ago)