Sharpness at 24mm

For this test, the Samyang AF 24mm F1.8 FE lens was attached to a Sony A7R IV 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 24mm

Centre sharpness is soft wide-open at f/1.8, slightly soft at f/2, and excellent from f/2.8 all the way through to f/11, with f/16 and particularly f/22 being adversely affected by diffraction.

The edges aren't quite as sharp as the centre, with f/2.8 to f/11 producing the sharpest results.

Aperture	Centre Crop	Edge Crop
f/1.8
f/2
f/2.8
f/4
f/5.6
f/8
f/11
f/16
f/22