Sharpness at 12mm

For these sharpness tests the Carl Zeiss Touit Distagon 2.8/12mm T* lens was attached to a Sony NEX-5R 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 full frame at 12mm

The centre is remarkably sharp wide open, with peak performance achieved in the f/4-11 range. Diffraction sets in at around f/16, with its effects becoming more visible at f/22.

The edges are somewhat soft at f/2.8 but sharpen up very nicely at f/4, with f/11 the optimum setting.

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