Sharpness at 16mm

The sharpness tests for this review were carried out using a real-world subject rather than a test chart. The Sigma 16-28mm F2.8 DG DN lens was attached to a Sony A7 IV camera 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 16mm

The centre is very sharp even when shooting wide open, so you can happily use f/2.8-f/11. Diffraction starts to set in at f/16 and especially f/22.

The edges aren't quite as sharp as the centre, being just a little soft at f/2.8, with f/4-f/11 the optimum settings.

Aperture	Centre Crop	Edge Crop
f/2.8
f/4
f/5.6
f/8
f/11
f/16
f/22