Sigma AF 24-70mm f/2.8 EX DG macro (Canon) - Review / Lab Test Report - Analysis
Lens Reviews - Canon EOS (APS-C)
Article Index
Introduction
Analysis

Distortion

The Sigma produces only moderate barrel distortion at 24mm (~1.3%) and slight pincushion distortion at 70mm (~0.7%). This is usually nothing to worry about in field conditions.

Move the mouse cursor over the focal length text marks below to observe the respective distortion
24mm 40mm 70mm

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

Vignetting

As mentioned above the Sigma is a classic full format lens and when used on APS-C DSLRs it can take advantage the usual sweet spot effect here resulting in a very low degree of vignetting throughout the zoom range. Interestingly the effect is most pronounced at 70mm although ~0.46EV @ f/2.8 is usually not field-relevant.

MTF (resolution)

The resolution figures of the Sigma are generally excellent in the center of the image field and very good at the borders. There's a bit of a performance drop at 70mm where the peak performance isn't as good anymore as at 24mm/40mm. At 70mm @ f/2.8 the contrast level seems to be slightly reduced. The peak performance is reached around f/5.6.

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)

The lens exhibits only a moderate degree of lateral chromatic aberrations (color shadows at harsh contrast transitions) with an average width around 1px at 24mm and 40mm. CAs are pretty much a non-issue at 70mm.

Verdict

The Sigma AF 24-70mm f/2.8 EX DG macro showed an impressive performance throughout all characteristics. It is a very sharp lens at all mainstream aperture settings. Distortions, CAs as well as vignetting are moderate and usually nothing to worry about. The build quality is very fine and the AF is pretty fast despite the enormous glass elements and a conventional AF micro-motor. The biggest problem of the Sigma is not performance but its scope. When used on APS-C DSLRs the zoom range (38-112mm) doesn't really qualify it as a standard zoom in the true sense although it surely has some appeal for press and basic portrait photography. It will be interesting to see how this lens will perform within the full format test scope.

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