Sharpness at 70mm

For this test, the Sigma 28-105mm F2.8 DG DN Art lens was attached to a Panasonic Lumix S5II 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 70mm

The centre is acceptably sharp wide open at f/2.8, with peak performance achieved in the f/4-f/11 range. Diffraction starts to set in at f/16.

The edges are almost as sharp as the centre, with f/4 to f/11 again being the optimum settings.

Aperture	Centre Crop	Edge Crop
f/2.8
f/4
f/5.6
f/8
f/11
f/16
f/22