Review by Klaus Schroiff, published May 2010

Introduction

In our previous tests it performed pretty well. But the initially released version relied on a fairly dated screw drive, which made it an unattractive choice for most Nikon DX users. Sigma upgraded the F-mount version of the lens to an HSM drive (the Canon variant uses a DC motor instead), but still the lens lacked one important feature: optical image stabilization. Well, it seems as if Sigma agreed here because they eventually released the Sigma AF 17-70mm f/2.8-4 DC HSM OS.

The build quality of the Sigma lens is pretty good - it's made of tightly assembled combination of metal and high quality parts. Like its predecessor it uses a duo-cam system to extend the lens when zooming towards the tele setting. You may notice that it's actually quite long at 70mm especially when mounting the supplied lens hood. There's only a very marginal wobbling in the zoom mechanism even in the most extreme setting. The two control rings have a smooth, pleasant action. The front element does not rotate. The focus ring is coupled to the AF mechanism so it rotates during focus operations. This is a point where the cost-cutting measurements get a little more obvious.

The 17-70mm OS features the slightly simplified version of Sigma's HSM ("hypersonic AF motor"). It is still fast and nearly silent but full-time manual (FTM) override is not possible in one-shot AF mode. The AF speed via in contrast AF (Live-View) is on the slow side. It is worth to mention that the lens carries a "macro" in its name. You shouldn't expect the performance levels of a true macro lens here but the Sigma can focus down to 0.22m which translates to a max. object magnification of 1:2.7 at 70mm. This is good enough for some basic close focus applications.

A major new feature is, of course, the OS ("Optical Stabilizer"). As already reported in previous reviews it is impressively efficient and as good as the corresponding genuine manufacturer implementations. Sigma claims a gain of 4-stops which doesn't seem to be unrealistic.

Here's a comparison between the non-OS and the new OS variant of the lens: