Sharpness at 400mm

For this test, the Canon RF 100-400mm F5.6-8 IS USM lens was attached to a Canon EOS R6 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 400mm

Center and edge sharpness are both very good wide open at f/8 and excellent between f/11 and f/22. At f/32 sharpness across the frame is beginning to drop-off a little due to diffraction, but is still commendably high.

Aperture	Centre Crop	Edge Crop
f/8
f/11
f/16
f/22
f/32
f/45