View full size The Sigma 17-70mm F2.8-4 DC Macro OS HSM is a premium fast 'normal' zoom for APS-C SLRs, which is designed as an upgrade for photographers who have outgrown the 'kit' zooms typically supplied with camera bodies. It was announced at Photokina 2012, as the first lens in Sigma's new 'Contemporary' category of compact general-purpose zooms for everyday photography.
It's a successor to a near identically-named lens from December 2009, the Sigma 17-70mm F2.8-4 DC Macro OS HSM, but is smaller and lighter, uses revised optics, and has a new cosmetic design. Prior to this Sigma made the unstabilised 17-70mm f/2.8-4.5 DC, a lens which was very highly regarded in its time.
The latest 17-70mm offers some pretty clear advantages over the average 18-55mm F3.5-5.6 kit lens. It provides extra zoom range, being both slightly wider and usefully longer in the telephoto range. Its F2.8-4 maximum aperture range means it gathers more light - twice as much at the long end, and 2/3 stop at wideangle. This offers advantages for both low light shooting, and getting blurred backgrounds when shooting subjects like portraits. It also offers unusually close focusing to just 22cm (hence the word 'Macro' in the lens name).
The lens use Sigma's 'Hypersonic Motor' for quiet autofocus, and is available to fit Canon, Nikon, Pentax, Sigma and Sony cameras. The Canon, Nikon and Sigma versions all feature built-in optical image stabilisation, to allow shooting at slower shutter speeds than usual without image degradation from camera shake. The Pentax and Sony versions don't have OS, and rely on the camera's built-in stabilisation systems instead. (Note that the lens won't autofocus on old Pentax DSLRs that don't have the requisite electrical contacts to power the focus motor.)
The 17-70mm doesn't have many direct equivalents from the camera manufacturers - the closest is the Pentax smc DA 17-70mm F4.0 AL (IF) SDM - and offers an interesting middle ground between upgrading to an extended range zoom such in the 16-85mm class, or a fast zoom like a 17-50mm F2.8. It's also pretty reasonably priced. So is it the ideal compromise choice, or just too good to be true? Read on to find out.
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