Quote Originally Posted by Loose Gravel
You might put a 45 neg holder in the enlarger and see if the rings are still there. Of course, the blacker the better inside your enlarger. I don't know about paint on bellows. Black baffles made of thin shim stock is something telescope makers use to reduce stray light. I don't know where they would go in a Devere, as I don't know these enlargers.

The rings are clearly evident with the 5x4 holder in place.
I vacuumed the inside of the bellows this morning (very dusty) and cleaned all internal surfaces and will experiment again tonight.