Sharpness at 24mm

For this test, the Tokina Opera 16-28mm F2.8 FF 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 24mm

Centre sharpness remains high through from f/4 to f/11, with f/16 and f/22 being adversely affected by diffraction. The edges aren't quite as sharp as the centre, with f/5.6-f/11 producing the sharpest results.

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