I try to keep it simple. I have a Nikkor 120, Schnieder 210, Fuji 300tele and an old 135 that someone gave me. I don't use the 135 too much. They are used on a Toyo 45A field camera for which I have the rear extension accessory when extra bellows length is needed for close-up. Remember that you need to compensate exposure for bellows extensions so keeping track for different camera/lens combinations is something I would rather not do. What I did was to do the math for each of the first three lenses I mentioned by f/stop changes and marked the compensation on a small retractable ruler with a different color permanent marker. When shooting I just "measure" with the tape from the lensboard to the film plane and read the closest compensation color coded for that lens. I have happily forgotten the equation --- one less thing to store in my memory bank.