Ok, not to be contrary, but I want to do this completely
differently.....  For me, since my mono-rail doesn't have a
built-in ruler, I would find it much easier to just have a table
for *subject distance*. I think I could accurately guesstimate
subject distance better than bellows draw (image distance). Why
does no one do this? Why is the sky blue?  Having a table
divided by 1/3 stops would also be nice. So, if I have a row of
desired exposure compensations (like 1.33, 1.66, 2, 2.66, etc...
all the way up to 16 let's say, a.k.a 4 stops) and I know my
focal length (180mm), I should be able to calculate for subject
distance, right?  Can anyone do the algebra and concoct a
singular formula? I was having to convert exposure compensation
to magnfication and then to subject distance and at about 2
o'clock in the morning I was beginning to lose my patience.