Having interchangeable backs is a considerable advantage if you shoot more than one type of film, or if you do not want to stall for a few minutes mid-shoot to change film rolls. I have four backs for my Mamiya 645 AFD II. I load them with TMax400 and Acros, FP4+ and TriX. Occasionally I replace the FP4+ and TriX with colour film, either slide or negative.
Originally Posted by abhishek@1985