I see backs available on Ebay (UK) for about $100 including shipping. I could mount Nikon SLR's and DSLR's on my 4x5. The only advantage I can see is closeup photography. My widest lens is a 90mm f6.8. I assume I would need a super-expensive wide angle to obtain a normal view with 35mm. Anyone using a 35mm SLR back, either store bought or home-made?