MSA Friends: In our teaching microscope collection, we have two of the older Nikon Labophot-POL polarized scopes that have a peculiar issue. I have attached an image to illustrate the problem: in plane light, there are faint interference colors!! Even weirder, the interference colors are different in each eyepiece. The right eyepiece shows fainter versions of the interference colors displayed in XPL. The left eyepiece shows faint interference colors that are about 100nm longer in wavelength than the right eyepiece. This makes the scopes unusable for students (too confusing and causes eyestrain), so we'd like to repair them. After fiddling around with the components, I have isolated the problem to unexpected optical interference within the "intermediate tube", which is the disc between the eyepieces and main arm that contains the accessory plate and analyzer (see attached). When I replace the bad intermediate tube with a good one from another scope, the problem goes away. There are two fixed lenses in the intermediate tube, and the simple interpretation is that one of them is damaged or misaligned (which is weird because I would assume they are just anisotropic glass), or perhaps there are strange polarizing reflections happening in the flight path. I can't diagnose anything by visual inspection: good tube and bad tube are indistinguishable to me. Has anyone experienced this problem before and/or does anyone know what's going on? If so, was it repairable? Or do I just look for a replacement intermediate tube? I'm hoping that someone out there can help troubleshoot before I go down a deep rabbit hole on Etsy looking for vintage replacement parts. Thanks to all! Happy summer, Codi ______________________________________ Codi Lazar Associate Professor Department of Geological Sciences California State University, San Bernardino