I like to use mine for paper negatives. Cut a strip off the long side of a piece of 5x7 paper and just lay it in the back over the film gate.
That would probably work for 5x7 film too.
I made a "holder" out of black construction paper to hold a piece of cut down 4x5 film, and it works, but there were a couple inconvenient things about that for me:
- The film is just a hair too wide to fit in my stainless steel tank for 120.
- My enlarger can't cover the whole frame, and the corners are soft for what it does cover with my 105mm enlarging lens.
But it's great for paper negatives and makes really nice "postcard" sized contact prints!
If I had a bigger enlarger, I'd probably pursue the 5x7 film option.