I've been exposed to Newton's rings before with an old Paterson enlarger, but my question does not involve a near negative-to-glass contact. On my Beseler CB-7 and 45 MXII, the heat-absorbing glass is separated from the upper condenser by a spacer ring -- probably 1/16-1/8" thick. I'm wondering why the spacer is there. I don't see how it would produce Newton's rings if removed. I could run some tests myself, but I thought someone here would have an explanation for the spacers. It is probably just to avoid scratches. Any thoughts?