When I recently broke out my RB gear to start doing some new B&W work, I discovered that I am missing a few dark slides. When I went to eBay to look, I discovered that whole backs are about the same price as slides! No problem, I bought a back for under $20. The slide is just fine but, although I barely care, the back isn't what was described. The only issue is that this is a 220 back and I really don't shoot any 220 film anymore. So . . . What happens if I put 120 film through the 220 back? Will the thickness of the paper backing be a problem mechanically? Will it be a focus issue? I think that I remember addressing this YEARS ago when I was using these cameras for wedding work but I don't remember the answer. Thanks . . .