Sigma AF 105mm f/2.8 EX HSM DG OS macro (Canon EOS) - Full Format Review - Analysis
Lens Reviews - Canon EOS (Full Format)

Distortion

Typical for most macro lenses the level of distortion is negligible and nothing to worry about.

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

Vignetting

The amount of vignetting comparatively moderate on a full format body but in absolute terms it's still very pronounced at f/2.8 (1.7EV). The problem is significantly improved at f/4 and negligible from f/5.6 onward.

MTF (resolution)

The resolution characteristic of the Sigma EX lens is very good and pretty much comparable to the Canon EF 100mm f/2.8 USM L IS. The center quality is excellent all the way up to f/8. The outer region is "only" good to very good at f/2.8 but reaches a very good maximum at f/8. Starting from f/11 onwards there's the general decrease in quality due to diffraction effects. However, the lens remains easily usable at f/16. f/22 is usable but should be avoided if possible.

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 are very well controlled with an average width of around 0.2px at the image borders. This is nothing to worry about at all.

Bokeh

The bokeh (the quality of the out-of-focus blur) is a primary aspect for a macro lens and the Sigma lens does not disappoint us here.

Out-of-focus highlights have a smooth inner zone with only a marginal outlining effect at the highlight borders. The highlight shape is circular in the image center but it deteriorates towards "cat's eyes" towards the borders of the image field - a vignetting effect which is actually more pronounced than usual on the Sigma. It helps to stop down to improve the issue.

The general blur in the focus transition zone is very smooth and buttery - this is especially true for the background blur.

Bokeh Fringing / Longitudinal Chromatic Aberrations (LoCA)

Bokeh fringing is a common problem present in most large aperture lenses - it is typically visible as green and purple halos in the out-of-focus zones. However, the Sigma does a better job than usual here although you can still spot a bit of fringing at f/2.8.

Move the mouse cursor over the f-stop marks below to observe the respective LoCAs
f/2.8 f/4 f/5.6




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