Sharpness at 14mm

For this test, the Canon RF 14-35mm F4L IS USM lens was attached to an Canon EOS R5 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 14mm

The centre is pleasingly sharp even wide open at f/4, with peak performance achieved in the f/5.6-f/11 range. Diffraction sets in at f/16.

The edges are almost as sharp as the centre, with f/5.6 to f/11 the optimum settings.

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