Sigma AF 180mm f/3.5 EX HSM APO macro - Review / Test Report - Analysis
Lens Reviews - Canon EOS (APS-C)

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).

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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