You're right about the Mamiya 7 being "large." It's still small for MF camera when compared to SLRs but larger than the Mamiya 6 which the lens can collapse. The RF645 is smaller than the Mamiya 6 but the lens does not collapse. I'd decide first what format you'd prefer to shoot, then go from there. The Fuji 645's are quite a bit cheaper than the RF645 and if you only want one lens that may be the way to go, IF you want to shoot 6x4.5.