Sharpness at 400mm

The sharpness tests for this review were carried out using a real-world subject rather than a test chart. The Canon EF 400mm f/4 DO IS II USM lens was attached to a Canon EOS 5DS 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 400mm

Our sharpness test shots turned out disappointingly soft at f/4 and f/5.6, despite shooting multiple frames and using every possible measure to prevent camera shake. As our real world sample images at these apertures were very sharp, we suspect the softness during sharpness testing is likely due to an autofocussing anomaly, compounded by the extremely limited depth of field at this focal length when using large apertures.

At f/8, detail really pops, and the lens maintains excellent sharpness until f/22 where diffraction softens things very slightly. At all apertures, corner sharpness is near-identical to the centre of frame.

Aperture	Centre Crop	Edge Crop
f/4
f/5.6
f/8
f/11
f/16
f/22
f/32