Sigma AF 70mm f/2.8 EX DG macro - Full Format Lab Test / Review - Analysis
Lens Reviews - Canon EOS (Full Format)
Article Index
Introduction
Analysis

Distortion

Typical for macro lenses the Sigma shows an extremely low level of distortion which is absolutely negligible in field conditions.

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

Vignetting

The Sigma lens produces some vignetting at max. aperture (1EV) but this is still comparatively moderate within the full format test scope. The problem is basically gone from f/4 onwards.

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/8 with a slight peak in the f/4-5.6 vicinity. Due to the usual diffraction effects the resolution is reduced to 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.

The tested sample showed a slight centering problem on the left side of the image field.

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 very well controlled within the full format testing scope. 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.

Bokeh

The bokeh (the quality of the out-of-focus blur) is a primary aspect for a macro lens and the Sigma lens does shine here. Out-of-focus highlights are very uniform and perfectly circular at f/2.8. The shape deteriorates a little at f/4 but edges are only really noticeable from f/5.6 onwards. The critical focus transition zones are very smooth even at max. aperture.

Bokeh Fringing / Longitudinal Chromatic Aberrations (LoCA)

Bokeh fringing is a common problem among large aperture lenses. However, the Sigma shows only traces of LoCAs at f/2.8 and the problem isn't really relevant anymore from f/4 onwards.

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

Verdict

The Sigma AF 70mm f/2.8 EX DG macro is capable to deliver exceptionally sharp results throughout most of the aperture range. The bokeh (out-of-focus blur) is very smooth and buttery and bokeh fringing isn't a really significant issue. Typical for macro lenses it also produces a negligible degree of distortions. Lateral CAs (color shadows at the image borders) are very low in absolute terms albeit a little higher than average for a macro lens. The Sigma lens has one distinctive weak sport - the AF. Its accuracy is fine but it is both very slow and noisy. The build quality is on a very high level thanks to a metal construction and tight tolerances.

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