Sharpness at 135mm

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 135mm

At the centre, the lens is very sharp wide open (f/5.6 at this focal length). It is excellent between f/8 and f/16, becoming ever so slightly softer at f/22.  At the narrowest apertures of f/32 and f/36, centre sharpness is softer again, but the overall impression of sharpness at normal printing and web sizes remains very good. Sharpness is also great at the edges, but is sharpest between f/8 and f/16, being ever so slightly softer from f/22 onwards.

Aperture	Centre Crop	Edge Crop
f/5
f/5.6
f/8
f/11
f/16
f/22
f/32
f/36