Math for figuring out 35mm lenses to Mamiya lenses

I hope the math is linear like you say, but I'm not sure. I think I might have to look at what my FX lenses are, and see if it is linear by finding the angle of view that comes close with the Mamiya lenses and work backwards. If I can make it work with a 2.1 like you say for a small sample, it would prove it to the point of being useful.

I don't think the f-stop would work with the crop. It's a ratio that works regardless of cameras and lenses. It may work for DOF though.