Thought I'd share a sample from this experiment - ran some lens calibration during the holidays, tried the Sigma 30mm on the 5D3 to see what the result looks like. The Sigma is physically compatible with the EF mount despite being designed for an EF-S crop sensor body. The corners are completely black, the image circle has an interesting vignetting effect, nicely sharp in the center where it was designed to work. This is f/1.4, 1/640 second, handheld, spot focus on red 0 after microadjusting +15. Illumination from a shoe mounted 12 LED video lamp. No post processing.
Sigma 30mm crop lens on a full frame sensor by hjl, on Flickr