Sharpness at 18mm

For this test, the Olympus M.Zuiko Digital ED 8-25mm F4.0 Pro lens was attached to an OM System OM-1 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 18mm

The centre is pleasingly sharp even wide open at f/4, with peak performance achieved in the f/5.6-f/11 range. Diffraction sets in at f/16.

The edges are almost as sharp as the centre, with f/5.6 to f/11 the optimum settings.

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