A while ago I had the chance to try out analog photography. Due to unknown reasons in development (likely a problem with one of the liquids) the resulting film negatives are very dark. That is, if I put my phone's flashlight at full intensity immediately behind it, the illuminated spot is just about at the right brightness (when viewed in a room at daylight).
I'd love to digitize that film using my DSLR with extension tubes. I had initially planned to use a phone or laptop screen as light box, then take a picture of the photo and invert it in Photoshop. In addition, a "flat field" sort of image could be made to correct for uneven illumination. However, neither turned out to be bright enough. I haven't yet tried what would happen if I simply exposed longer as another problem is the individual colors of each pixel on the screen become visible at the needed magnification. Thus, I don't have any light source available that is both bright enough and evenly illuminates the film.
I only have two rolls of 24 images each so I'd be fine with some method that is a little more complicated. Additionally, the images don't care huge sentimental value so the end quality needs not be perfect.
TL;DR: I want to digitize very underexposed film with my DSLR and don't have a bright enough even light source. What are some workarounds that I can use to make it work?