Sigma 24-70mm f/2.8 EX DG HSM

Gary Wolstenholme takes a look at Sigma's flagship standard zoom lens for full-frame cameras.

Sigma's 24-70mm f/2.8 EX DG HSM sports a fast maximum aperture of f/2.8 throughout the zoom range and silent HSM focusing. Being an EX lens it sits at the top of their professional zoom range and costs around £600.

Alternatives from other third party manufacturers include Tamron's SP 28-75mm f/2.8 XR Di, reviewed here which only costs £360, but doesn't have the silent focusing motor of the Sigma.

Competition from camera manufacturers include Canon's well regarded EF 24-70mm f/2.8L USM, which costs around £930. Nikon also make a 24-70mm f/2.8 which costs around £1190. Both have weather sealed build quality.

Sony users have the 24-70mm f/2.8 ZA SSM T* lens, which costs around £1500 due to the Carl Zeiss branding and technologies employed such as the T* coatings to reduce flare and improve contrast.

Sigma 24-70mm f/2.8 EX DG HSM: Handling and features
The design of Sigma's 24-70mm is more short and stubby than alternatives offered by other manufacturers. Although it's not any heavier than alternatives this wide 88.6mm  diameter barrel makes the lens feel quite chunky. High quality plastics have been used in the construction and much of the exterior has a smart powder coating effect applied to it. Although this finish looks really good when new, I find it marks easily, even with light use.

Focus is powered by a HSM motor, which provides fast, silent and accurate autofocus performance throughout the range. As focus is performed internally the front filter thread does not rotate, which should please users of polarising filters and neutral density graduated filters. The HSM motor used also allows for manual focus adjustments at any time and the focus ring does not rotate during AF, which I find helps with the handling of the lens.

The zoom mechanism is damped well and is very smooth to operate, only tightening slightly at the telephoto end of the range. I had no issues with zoom creep during use either as the mechanism provides ample resistance to prevent the lens zooming under its own weight.

Sigma 24-70mm f/2.8 EX DG HSM: Performance
At f/2.8 and 24mm the lens performs excellently in the centre, although the sharpness towards the edges lags behind a fair bit. Stopping down to just f/4 produces excellent sharpness across the frame and peak quality is achieved at f/5.6.

At 35mm the centre sharpness at maximum aperture drops off a little but is still good and the resolution towards the edges still lags behind. Just as with 24mm, stopping down to f/4 results in excellent sharpness across the frame and peak quality is achieved at f/8.

Finally, at 70mm, the sharpness at maximum aperture drops off considerably and is below my expectations for a lens of this level. Still if you are happy to stop down to f/4, the quality across the frame improves dramatically and is very good across the frame. Peak quality is again achieved at f/8, where the resolution is excellent across the frame.

Resolution at 24mm	Resolution at 35mm
Resolution at 70mm	How to read our graphs The blue column represents readings from the centre of the picture frame at the various apertures and the green is from the edges. Averaging them out gives the red weighted column. The scale on the left side is an indication of actual image resolution. The taller the column, the better the lens performance. Simple. For this review, the lens was tested on a Nikon D700 using Imatest.

Levels of chromatic aberration are kept below unacceptable levels throughout the zoom range. At their worst they cover 0.72 pixel widths at 24mm and f/2.8, which may show along high contrast edges towards the edges of the frame.

Chromatic Aberrations at 24mm	Chromatic Aberrations at 35mm
Chromatic Aberrations at 70mm	How to read out charts Chromatic aberration is the lens' inability to focus on the sensor or film all colours of visible light at the same point. Severe chromatic aberration gives a noticeable fringing or a halo effect around sharp edges within the picture. It can be cured in software. Apochromatic lenses have special lens elements (aspheric, extra-low dispersion etc) to minimize the problem, hence they usually cost more. For this review, the lens was tested on a Nikon D700 using Imatest.

As I would expect for a wide aperture lens, falloff of illumination towards the corners can be quite pronounced. At 24mm and f/2.8 the corners are 2.51 stops darker than the image centre and the lens needs to be stopped down to f/5.6 to achieve visually uniform illumination. At 70mm and f/2.8 the corners are 2.2stops darker than the image centre and the lens also needs to be stopped down to f/5.6 for visual uniformity.

Distortion may pose issues for some at 24mm. Here Imatest recorded 6.41% barrel distortion, which is fairly typical if a lens of this type. At 70mm the barrel distortion is replaced with mild pincushion distortion. Here Imatest recorded 0.782% pincushion distortion, which shouldn't pose too many issues in normal photography. Luckily the distortion pattern is uniform throughout the zoom range, making it easy enough to correct in image editing software afterwards.

Click on the thumbnails for a high resolution image.
The resolution in the centre is excellent at every aperture at 24mm.		At other focal lengths, and especially at 70mm, the lens needs to be stopped down to f/4 for best results.

Flare and ghosting is reasonably well controlled under normal conditions. In extreme cases with strong point sources of light within the frame flare can be a problem, with patterns of flare littering the image. This is only really an issue in very extreme cases, such as shooting into stage lighting, or when the sun is very prominent in the frame. A petal shaped lens hood is supplied, which does an excellent job of shielding the front element from extraneous light.

Sigma 24-70mm f/2.8 EX DG HSM: Verdict
Summing this lens up in a paragraph or two is actually quite difficult, as it's almost like I've tested two completely different lenses at once. The first one being an f/2.8 zoom lens, which should be great for low light photography, but unfortunately falls slightly below par in terms of performance, especially at focal lengths beyond 35mm. Here the resolution at maximum aperture just isn't what you'd expect for a flagship lens from any lens manufacturer.

Now if I were to consider this lens as having a maximum aperture of f/4, it would be amongst the best performing lenses covering these focal lengths. Sharpness across the frame is excellent.

It's a shame this lens has this split personality as the build quality is generally very good, and the lens is very pleasant to use.

So in summary, if you were after a high performance f/2.8 lens, you may find better performance elsewhere. On the other hand, if your photography allows you to stop down to f/4 or smaller much of the time, then this lens is a superb performer.

Sigma 24-70mm f/2.8 EX DG HSM: Pros
Excellent optical performance stopped down to f/4 and below
Good build quality
Fast autofocus

Sigma 24-70mm f/2.8 EX DG HSM: Cons
Resolution at maximum aperture at focal lengths beyond 35mm
Barrel Distortion at 24mm

FEATURES
HANDLING
PERFORMANCE
VALUE FOR MONEY
OVERALL

Sigma 24-70mm f/2.8 EX DG HSM: Lens specification

Price	£600.00
Contact	www.sigma-imaging-uk.com
Filter size	82mm
Format	Full Frame
Construction	14 elements in 12 groups
Angle-of-view	84.1 - 34.3 degrees
35mm equivalent focal length (on APS-C body)	36-105mm
Internal focusing	Yes
Image stabilisation	No
Minimum focus	38cm
Maximum aperture	f/2.8
Minimum aperture	f/22
Weight	790g
Size	88.6 x 94.7mm
In the box	Lens Case, Lens Hood

The Sigma 24-70mm f/2.8 EX DG HSM costs around £600 and is available from Warehouse Express here:

Sigma 24-70mm f/2.8 EX DG HSM for Canon
Sigma 24-70mm f/2.8 EX DG HSM for Nikon
Sigma 24-70mm f/2.8 EX DG HSM for Sigma
Sigma 24-70mm f/2.8 EX DG HSM for Sony
Sigma 24-70mm f/2.8 EX DG HSM for Pentax

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