Sharpness at 400mm

For this test, the Tamron 50-400mm F/4.5-6.3 Di III VC VXD lens was attached to a Sony Alpha 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 400mm

Center sharpness is excellent between f/6.3 and f/16. At f/22 sharpness drops off due to diffraction.

Edge sharpness is almost as good as in the centre, with the sharpest results between f/8 and f/16.

Aperture	Centre Crop	Edge Crop
f/6.3
f/8
f/11
f/16
f/22
f/32