Sharpness at 100mm

For this review, the sharpness test is carried out by photographing a real-world subject, rather than a test chart. The Sony FE 100-400mm F4.5–5.6 GM OSS lens was mounted on a Sony A9, which was in-turn mounted on a sturdy tripod. Exposure delay was activated to prevent camera-shake. Any changes in tone you might see across the crops are due to natural light changes during the shooting session.

The full frame at 100mm

Sharpness is excellent for this lens. At wide open at 100mm (f/4.5), centre sharpness is very good, becoming slightly sharper again at f/8. Sharpness remains excellent up to f/16, dropping off slightly at f/22 and becoming slightly soft at f/32. It's likely that you'll only notice this softness if examining at 100%.  At the edges, the sharpest results can be seen between f/16 and f/22.

Aperture	Centre Crop	Edge Crop
f/4.5
f/5.6
f/8
f/11
f/16
f/22
f/32