Sharpness at 400mm

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 400mm

At the furthest reach of the lens, centre sharpness is at its best between f/8 and f/16, but it is still excellent at f/5.6 and f/22. There’s more obvious softness at f/32 and f/40, but you might be able to get away with it at normal printing and web sizes. For edge sharpness, the best results can be seen between f/8 and f/22.

Aperture	Centre Crop	Edge Crop
f/5.6
f/8
f/11
f/16
f/22
f/32
f/40