Well, I been thinking about this, too... Trying to figure out a good way to make 5x7 contacts on an 8x10. The most problematic part for me is to get the neg centered on the paper. But if one gets a piece of heavy glass and makes this opaque frame on top of it, as Eric says, might work pretty well. If the glass is exactly 8x10 and the opaque part is centered. I think just a matt board on top of the glass could work, but that doesn't solve the centering issue.