excellent sharpness even wide open but best at 12mm, and even better when stopped down to f/5.6-8
corners less sharp as you zoom in
not as sharp as the Canon 11-24mm lens
well corrected CA and very good vignetting, only 2/3rds EV wide open - both better than the Canon lens
slight but complex barrel distortion at 12mm, almost disappears by 16mm, slight, complex pincushion at longer focal lengths - less than the Canon lens especially at widest zoom but more complex and more difficult to correct
measured T-stop for this lens is around T4.6-4.8