Sharpness at 40mm

For these tests, the Olympus 12-40mm f3.5-6.3 lens was attached to an Olympus OM-D E-M1 compact system camera, which in turn was mounted on a sturdy tripod. The self-timer was used to avoid any vibrations from pressing the shutter release. Slight tonal changes are due to slight changes in natural light during the session.

The full frame at 40mm

Centre sharpness is OK wide open at f/2.8, but peak performance is achieved until f/8. Diffraction kicks in at f/16 and gets worse at f/22. The corners are soft at f/2.8-f/5.6, with the best performance achieved at f/8.

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