Suggested backlight sources for scanning film with DSLR

Diffuser, lots of options, three sheets of tracing paper might work. Whatever you use, make it out of focus. Set up for flash, there are lots of options. I took an old furniture cabinet, cut a hole in the top and shine the flash up from underneath, see photo. Another guy has a glass dining table, flash up from underneath. White plastic cooler material (called “Styrofoam” here" is a great diffuser; you can cut a hole in a cooler, shine the light into the cooler, cut another hole and place film holder over 2nd hole. Or cut up the material, use it to line a diffusion box.