Sharpness at 400mm

For this test, the Sigma 100-400mm F5-6.3 DG OS HSM lens was attached to a Canon EOS 5D Mark III body, which in turn was mounted on a sturdy tripod. Exposure delay mode was activated. Tonal and colour variances across the crops are due to changes in natural light during the session.

The full frame at 400mm

Centre sharpness is a little soft wide-open at f/6.3. Both the centre and the edge remain high through from f/8 to f/16, with f/22 to f/29 being adversely affected by diffraction.

Aperture	Centre Crop	Edge Crop
f/6.3
f/8
f/11
f/16
f/22
f/22