Sigma AF 30mm f/1.4 EX DC HSM - Review / Test Report - Analysis
Lens Reviews - Canon EOS (APS-C)

Distortion

The lens showed a medium degree (1.5%) of barrel distortion. Nothing to rave about but quite acceptable.

The chart above has a real-world size of about 120x80cm.

Vignetting

As mentioned the AF 30mm f/1.4 EX DC HSM has a reduced image field on the sensor plane so it looses the sweet spot advantage of conventional lenses when used on APS-C DSLRs. As a consequence vignetting is quite pronounced at large aperture setting (f/1.4 to f/2) with a shading of EV 1.0 and EV 0.75 in the image corners. The effect can be visible in critical scenes. From about f/2.8 onwards vignetting is no issue anymore.

MTF (resolution)

The lens exhibited a quite mixed behavior in the lab. The image center showed a superb performance reaching and probably exceeding the image sensor resolution of the EOS 350D (8MP) - even at f/1.4 the center is already excellent. Unfortunately the borders and more so the extreme borders are never really able to catch up. At f/1.4 is borders extremely soft. As usual the situations improves towards medium aperture settings but not overly so. The borders are good by f/5.6 and very good at f/8. For a fix-focal lens this is slightly disappointing all-in-all.

Note: the chart has been revised due to an error in the analysis.

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)

CAs (visible as color shadows at harsh contrast transitions) can reach an average CA pixel width of more than 1 pixel at the image borders. This is about average but a fix-focal should be better here.




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