Sharpness at 20mm

The sharpness tests for this review were carried out using a real-world subject rather than a test chart. The Tokina AT-X 12-28mm F4 Pro DX lens was attached to a Canon EOS 7D DSLR camera, which in turn was mounted on a sturdy tripod. The self-timer was used to avoid any vibrations from pressing the shutter release. Slight tonal changes are due to slight changes in natural light during the session.

The full frame at 20mm

Centre sharpness at 20mm is acceptable at f/5.6 and best at f/8, while the edges are acceptably sharp from f/8 to f/11. Diffraction starts to kick in at f/16.

Aperture	Centre Crop	Edge Crop
f/4
f/5.6
f/8
f/11
f/16
f/22