Sharpness at 14mm

For these tests, the Olympus M.ZUIKO Digital ED 14-150mm f/4-5.6 II lens was attached to an Olympus E-M5 II body, which in turn was mounted on a sturdy tripod. The self-timer was activated. The 100% crops represent about 1/400th of the total frame area.

The full frame at 14mm

At the wide end of the zoom range, the image centre is very sharp already at f/4, and stopping down brings only a minimal improvement in lens contrast. Diffraction creeps in at f11 and becomes noticeable at f16. The f22 setting is best avoided.

The corners are a different story. They are pretty soft wide open and never really sharpen up, although stopping down to f/5.6-f/8 does bring appreciable improvements. The effects of diffraction once again become evident at f16, and f22 is clearly worse than the f/4 setting.  Given that depth of field is already vast at f/5.6, we see little reason to use f/22 at this zoom setting anyway (if you need to use a slow shutter speed in broad daylight, it is probably a better idea to shoot at f/8 and use a good quality neutral density filter).

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