I am having problems with 8x10 contact prints. Because of Newton rings, I replaced the glass on a Paterson contact printer with ANR glass. This is slighly thicker than the original glass and thus receives higher pressure from the foam bed below. As a result, the glass bends, creating a gap between paper and negative right in the middle of the print, which results in noticeable loss of sharpness compared to the edges. Question: What is a good contact printing frame for someone haunted by Newton rings? (I seem to have read something at some point about a frame with an inflateable bubble under the glass.) Thanks for your help.