Birefringence Viewer

This holds two camera lens filters parallel about 30mm apart. It is intended to hold two polarizing filters oriented perpendicular to each other so that the material under test can be placed between them to test for birefringence.

The object is currently configured to hold the 52 mm polarizing filters I have, but can be easily adjusted for whatever size filters you have by adjusting the values in the spreadsheet.

I have designed this because I have been digitally scanning some negatives and discovered that I had some from 1936, which means that they are definitely nitrate film. In researching nitrate film, I learned that if one has nitrate film, one should digitize it as soon as possible, and unless the film has historic value, it should be disposed of. When nitrate film gets old, it begins to decay, and out-gasses nitric acid, and other toxic substances. It is extremely flammable (same chemical compound as gun-cotton), and can spontaneously combust. Only keep this stuff around i