In this category we see a huge slip-up. Dealing with a full frame lens we expected low vignetting on the APS-C sensor of our Canon 20D. We couldn’t be further from the truth, though. By f/2.8 the vignetting amounts to as much as 32% so –1.1 aperture value. On stopping down the lens to f/4.0 the light fall-off in the frame corners decreases to 15%. Only using f/5.6 relative aperture makes the vignetting on the APS-C sensor fall to practically not bothersome level of 11%.
If the vignetting on APS-C can be as much as 32% we are afraid to think what happens on full frame…
