Sharpness at 14mm

For this test, the Samyang AF 14mm f/2.8 EF 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 14mm

Centre sharpness is acceptable when shooting wide-open at f/2.8, and very good from f/4 onwards, with f/16 and f/22 being adversely affected by diffraction. The edges aren't nearly as sharp as the centre, with f/8-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