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Sigma AF 70mm f/2.8 EX DG macro (Canon) - Review / Test Report - Analysis |
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Lens Reviews -
Canon EOS (APS-C)
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Page 2 of 3
Distortion
Typical for macro lenses the Sigma shows an extremely low level of distortion (~0.1%) which is
absolutely negligible in field conditions.
The chart above has a real-world size of about 120x80cm.
Vignetting
Thanks to the sweet spot behavior on APS-C DSLRs the vignetting is very well controlled here.
The lens remains perfectly usable in this respect even at max. aperture (f/2.8).
MTF (resolution)
Macro lenses tend to be stellar performer thanks to a usually very conservative
max. aperture and the Sigma follows this tradition. The resolution characteristic
is generally excellent straight from f/2.8 all the way down to f/11 with a slight
peak in the f/4-5.6 vicinity. Due to the usual diffraction effects the resolution
is reduced to very good levels at f/16 and good quality at f/22.
Please note that the resolution tests are performed at conventional focus distances.
True macro tests are not possible at this stage.
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)
Lateral CAs (color shadows at the image borders) are relatively well controlled although
an average pixel width of around ~0.75px at the borders isn't really low for a fix-focal
lens. However, the problem is still not overly field-relevant.
There're only very minor traces of purple fringing at f/2.8.
Please note that lateral CAs can be corrected without any significant impacts via tools.
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