Sharpness at 300mm

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 300mm

At 300mm, centre sharpness is best between f/8 and f/16, being slightly softer at f/5.6 (wide open) and from f/22 to f/32. At the narrowest aperture of f/40 it’s softer again, but at normal printing and web sizes, you could get away with it. At the edges, sharpness is best between f/8 and f/16, with some slight softness at f/22.

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