I have an Mamiya RB67 camera, and use it just every so often. It's my first film camera. I also shoot 4x5 as well. With regard to my RB camera and the film back, do they have different film backs for it? I don't mean 120 -vs- 220. My current 120 back, say's 645 on it. Are there larger format sizes that will accommodate my RB? Does that make the image size larger as well? Sorry for the newb question, but I've never really shot a lot of film.