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Sigma AF 19mm f/2.8 EX DN (Sony E mount) - Review / Test Report - Analysis |
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Lens Reviews -
Sony NEX
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Page 2 of 3
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.
Please note that the MTF results are not directly comparable across the different systems!
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.
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