Sharpness

The sharpness tests for this review were carried out using a real-world subject rather than a test chart. The Canon EF 28mm f/2.8 IS USM lens was attached to a Canon 5D Mark III body, which in turn was mounted on a sturdy tripod. Self-timer mode was activated. Slight tonal changes are due to slight changes in natural light during the session.

The full frame at 28mm

Center sharpness is outstanding even wide open and nothing short of excellent between f/4 and f/11. At f/16 sharpness is still commendably high, although it drops off at f/22. Edge sharpness isn't quite so good, with poor results at f/2.8-f/5.6, requiring you to stop down to f/8 to get the best image quality, and again f/22 is worth avoiding.

Aperture	Centre Crop	Edge Crop
f/2.8
f/4
f/5.6
f/8
f/11
f/16
f/22