Time to match the new lens to the camera bodies, so fire up the FoCal. It is once you are used to the software quite simple to use, even easier if you have a camera that supports fully automatic AF micro Adjustment. Set up your target, hook up the camera to the computer and away you go.
After you have done a series of photographs at different levels of adjustment the software calculates what the final adjustment should be (on Canon if you are adjusting zoom you repeat the process for the Wide & Telephoto end).
The software is capable of a number of tests, including calculating what is the best performing aperture.