Hi, I’d like to begin with a disclaimer: Use this info at your own risk (although not too much of a risk - in worst case you’ll end up with some bad exposures).

I’ve never experienced studio lights or metering in real life, but I’m interested in photography, math and general problem solving so I gave it a shot.

My understanding is that you begin with two known parameters: The desired ratio between two strobes and the desired aperture when both strobes fire. Based on some assumptions and simplifications I ended up with two fairly simple formulas:

f1 = sqrt[R/(1+R)] * f
f2 = sqrt[1/(1+R)] * f

R is the desired ratio and f is the desired resulting f number. f1 and f2 are the f-numbers corresponding to each of the single strobes.

An example to illustrate: Assume that you’d like a ratio of 3 between main and fill, and that for some reason you’d like to use f/6.3 for the shot. According to these formulas you’d get f1 = 5.5 and f2 = 3.2. (In practice you’d have to round off 5.5 to the nearest f-stop 5.6.)

Adjust the power of the main light only to get the exposure right at f/5.6 and adjust the fill light only to give the right exposure at f/3.2. Then stop down to the desired f/6.3 and fire both strobes. If I’ve got it right you should get something similar to what you wanted. (But on the other hand, I might as well be completely wrong...)