This may be the right thread for my problem even if it doesn't concern Newton rings. When I enlarge negatives , full size with the black border, using a glass neagative carrier with glass on both sides the following happens. If there is a highlight area that extends all the way out to the edge, I get a thin dark shadow on the picture area along the edge. I have a feeling that this is some kind of a "light piping" phenomenon caused by the difference between the transparent film surrounding the negative and the almost totally dark highlight area. It appears mostly on my Leitz Focomat IIC with an Ilford 500 multigrade head but also on the Durst 805 B/W with condenser. If I use glasless carriers it doesn't occur.
Does anyone recognize the problem and do you have a suggestion for a cure ? Thank you in advance.