Sharpness at 28mm

For this test, the Sigma 28mm F1.4 DG HSM lens was attached to a Canon EOS 5DS R 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 28mm

Centre sharpness is a little soft wide open at f/1.4, but remains high through from f/2 to f/8, with f/11 and f/16 being adversely affected by diffraction. The edges are just as sharp as the centre, with f/2 to f/8 again producing the sharpest results.

Aperture	Centre Crop	Edge Crop
f/1.4
f/2
f/2.8
f/4
f/5.6
f/8
f/11
f/16