I used these to mount my 35mm film for scanning with my DSLR. Each compartment holds up to 6 frames, so I cut the negative film roll into sections of 6 frames. To use the trays, open them, carefully place the foil in the tray (the tray has small notches that fit the notches in the foil), then close the tray and squeeze until the foil clicks into place. I paired this with a cheap $20 LED-lit tracking bar, and it illuminates the negatives just enough for my camera on a tripod to get a good shot. It made the process very easy and I will definitely be buying them again.