Here's a puzzler for you, or maybe just for me:

I shoot almost all medium format, but due to a need to a) keep expenses down; b) shoot more frames; and, c) get a bit more tooth and grain in the prints, I wanted to shoot 35mm, but match the shallow depth of field I get with my RZ. Now, assuming that you had normal lenses on both cameras, is there a scientific way (other than trial and error) that one would go about matching DOF?

For example, if I am focused on a subject five feet away with the RZ with a 90mm lens, and I switch to my Canon with a 50mm lens and maintain the same distance, is there an equation of some sort that would convert f5.6 on the RZ to f-whatever on the Canon?

Thanks in advance to youse!