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Sigma AF 180mm f/3.5 EX HSM APO macro - Review / Test Report - Analysis |
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Lens Reviews -
Canon EOS (APS-C)
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Page 2 of 3
Distortion
As to be expected from a fix-focal lens and especially for a macro lens the level of
distortion is absolutely negligible.
The chart above has a real-world size of about 120x80cm.
Vignetting
On the EOS 350D with its reduced format (APS-C) the (full format) lens exhibits very
little vignetting at f/3.5. From f/5.6 & up the issue is pretty much negligible. There's
marginally less vignetting at 1:1 macro setting compared to infinity focus.
MTF (resolution)
Macro lenses tend to be sweet performers regarding resolution and that's also true
for the AF 180mm f/3.5 EX APO macro. At f/3.5 the resolution figures are already
very-good increasing further to medium aperture settings where the quality
scratches the resolution limits of the 350D's 8MP sensor. Beyond f/8 diffraction is
the limiting factor but the resolution is still very decent at f/16 and usable at
f/22. The lens provides a f/32 setting but it should be generally avoided due to
the rather soft image quality here (a normal behaviour).
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)
It came by surprise but CAs (color shadows at harsh contrast transitions) are a very
weak spot of the lens. At large aperture settings the issue is quite well controlled
but from f/8 & up the level of CAs is quite extreme peaking beyond 1.5 pixels at the
image borders. This behaviour is quite unusual for a fix-focal lens. The CAs had
a very even distribution in the tested sample so correcting the issue via an imaging
tool shouldn't be a big deal but the lens performed a little disappointing here nonetheless.
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