Sigma AF 19mm f/2.8 EX DN (Sony E mount) - Review / Test Report - Analysis
Lens Reviews - Sony NEX

Distortion

The Sigma lens produces a moderate amount of barrel distortion (~1.8%) which can be visible e.g. during architecture photography. However, it is certainly no show-stopper for most use-cases.

Vignetting

The light fall-off is comparatively heavy at f/2.8 (~0.9 f-stops) - this will be noticeable in some field images. Stopping down eases the issue a little bit it doesn't go away completely.

MTF (resolution)

The resolution characteristic of the Sigma AF 19mm f/2.8 EX DN is a bit on the odd side. On the one hand we have an exceptionally high center performance straight from f/2.8 onward. The lens is capable of keeping this level all the way to f/8. On the other hand the borders and more so the corners are weak especially at f/2.8. Stopping down helps, of course, but the quality does not exceed good levels here.

The centering quality of the tested sample was good and there's only a slight degree of field curvature.

Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations

Chromatic Aberrations (CAs)

The Sigma lens produces a quite high amount of lateral CAs (color shadows at harsh contrast transitions) with an average pixel width of around ~1.7px at the image borders. This will be visible in certain scenes but remember that this can be corrected during image post-processing.