I have a few small marks on my negatives that I can't figure out. They are usually in the same area of the negative and appear as a round darkspot on the 8x10 negative. They are about 1/8 inch in diameter and not super dark, just enough that you can see them. They are not sharp but very out of focus, almost like a very out of focus highlight. I don't think they're glare, but my best guess is a small bellows leak. Any ideas?