Sharpness at 10mm

For these sharpness tests the Nikon 10-20mm lens was attached to a Nikon D500 camera body, which in turn was mounted on a sturdy tripod. Slight tonal changes are due to slight changes in natural light during the session. The 100% crops represent about 1/500th of the total frame area.

The full frame at 10mm

At 10mm the image centre is actually pretty sharp, and the effects of diffraction start to be visible already at f/8. The f11 setting is still quite usable, but sharpness goes downhill from there.

The edges are somewhat soft wide open at f/4.5 but sharpen up quite nicely upon stopping down to f/8. Diffraction takes its toll at f11 and smaller apertures.

Aperture	Centre Crop	Edge Crop
f/4.5
f/8
f/11
f/16
f/22