Is there such thing as an adapting holder that would allow inserting a 4x5 film holder in a 5x7 spring back? This could be more convenient and lighter than having to carry and switch backs when shooting both formats (with perhaps the downside of an off centred frame, not too bad for these two formats) ? The cassettes have the same groove size, so this should be technically possible... Has someone seen this? Would it be asking too much if this adapter could also take a QuickLoad holder? Or even a Sinar 6x12? Yeah, I know... I still believe in Father Christmas!