Sharpness at 18mm

The sharpness tests for this review were carried out using a real-world subject rather than a test chart. The Canon EF 11-18mm f/4L 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 18mm

Center and edge sharpness are excellent wide-open at f/4 and nothing short of outstanding between f/5.6 and f/11. At f/16 and f/22 sharpness across the frame is beginning to drop-off due to diffraction, but is still commendably high.

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