Sharpness at 100mm

The sharpness tests for this review were carried out using a real-world subject rather than a test chart. The Canon EF 100-400mm f/4.5-5.6L IS II 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 100mm

Center and edge sharpness are both excellent wide open at f/4.5, and outstanding between f/5.6 and f/11. At f/16 sharpness across the frame is beginning to drop-off a little due to diffraction, but is still commendably high. F/22 and f/32 are best avoided.

Aperture	Centre Crop	Edge Crop
f/4.5
f/5.6
f/8
f/11
f/16
f/22
f/32