Sharpness at 50mm

For this test, the Sigma 18-50mm F2.8 DC DN Contemporary lens was attached to a Sony Alpha A6000 body, which was in turn mounted to a sturdy tripod. Exposure delay mode was activated. Tonal and colour variance across the crops are due to change in natural light during the session.

The full frame at 50mm

Center sharpness is a little soft at f/2.8, but outstanding between f/4 and f/11. At f/16 and especially f/22 sharpness drops off due to diffraction.

Edge sharpness isn't quite as good as in the centre, with the sharpest results between f/5.6 and f/11.

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