hi, just got my M1L including 2*210mm MFR-210. Cool!
I'm going to use sigma 15mm 2.8 with canon 5D mark III (no ext.battary pack) as well as longer lenses. Am I right that 170mm MFR is necessary to avoid edge's appearance in the picture? best, Dmitry.
There are different ways to Rome. I am a Nikonian, so I I do not have data for you. I tested several Nikon bodies, some do the job with MFR170. The rail might to be seen in the pictures but does not show in the stitch. You have to test it.