Sharpness at 300mm

For these tests, the Olympus M.ZUIKO Digital ED 300mm f/4 IS Pro 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 300mm

Center sharpness is commendably high from f/4 onwards, with peak performance achieved at f/8. Diffraction kicks in at f/16 and gets worse at f/22. The corners are also very sharp at f/4, with the best performance again at f/8.

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