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Sigma AF 30mm f/1.4 EX HSM DC - Review / Test Report - Analysis |
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Lens Reviews -
Canon EOS (APS-C)
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Page 2 of 3
Distortions
The lens showed a medium degree (1.5%) of barrel distortions. 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 HSM EX DC 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 MTF findings. The chart shows in line widths
per picture height (LW/PH) which can be taken as a quantity for sharpness. If you want to
know more about it 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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