The 18-35mm follows in the same design idiom as Sigma's most recent lenses such as the 35mm F1.4 DG HSM. The section of the barrel between the mount and the zoom ring is metal, and the central section is composed of Sigma's 'Thermally Stable Composite' in an attempt to balance strength and weight. Rubber grips on the focus and zoom rings, combined with a high level of fit and finish, bring a sense of quality to proceedings. As always, on Sigma lenses, the mount itself is plated brass.
In terms of design and control layout the lens is decidedly conventional, with a large manual focus ring at the front, a zoom ring placed closer to the camera body, and a distance scale and focus mode switch placed between the two. As usual for this class focusing is internal; less conventionally for a normal zoom, so is zooming, which means that the lens stays the same length at all times.
On the camera
There's no denying that the 18-35mm is a pretty large lens - it's 10mm longer than the Tamron 24-70mm F2.8. It's also a fairly heavy lens - essentially the same weight as the more rangey Tamron. However it balances pretty well on high-end SLRs such the Canon EOS 7D shown left, helped by the camera's substantial hand grip. We suspect it's likely to be found on this class of camera most of the time.
On smaller, lighter entry-level SLRs such as the Canon EOS 650D, the overall balance becomes more front-heavy, meaning you'll often find yourself supporting the camera by cradling the lens itself. Frankly, these models tend not to have hand-grips that are comfortable to hold for long periods anyway, so this encouragement to support the lens is no bad thing.
For a better idea of its size, here's the 18-35mm lined up alongside Sigma's 17-50mm F2.8 EX DC OS HSM and the recent Tamron SP 24-70mm F/2.8 Di VC USD. It's the narrowest in diameter but longest of the three, and weights almost as much as the full-frame Tamron.
Against the slower Sigma, the 18-35mm is considerably longer, and weighs 40% more. However, its more substantial build makes it more akin to the aged Nikon AF-S DX Nikkor 17-55mm f/2.8G, compared to which it's only 1cm / 0.4" longer, and 7% heavier.
Comparing the 18-35mm on a mid-range APS-C body to the Tamron 24-70mm F2.8 on one of the latest, similarly enthusiast-focused full frame DSLRs, there's essentially no difference in overall bulk. The small differences in weight and and length between the lenses make no appreciable difference to the handling, either. The main difference lies in the 18-35mm's internal zoom design, whereas most 24-70mm F2.8s extend substantially on zooming.
The 18-35mm uses Sigma's 'Hypersonic Motor' for autofocus, which is fast, essentially silent, and generally very decisive. The focus can be adjusted manually when the lens is set to AF without fear of damaging its innards. Our sample showed no obvious problem with systematic front- or back-focusing, but we did have some problems with focus consistency when shooting at large apertures (described later in the review).
The 18-35mm also works pretty well for live view autofocus, although this is highly dependent upon the camera being used. In video mode, it's not too bad either, indeed probably one of the better SLR lenses we've used. But if you use autofocus during movie recording in a quiet situation, the camera's built-in microphone will be liable to pick up the ticking of the lens's AF motor on your soundtrack.
Lens body elements
USB Dock compatibility
The 18-35mm is compatible with Sigma's unique USB dock, a relatively inexpensive accessory (£40 / $59 / €60) which allows you to hook Sigma's latest lenses up to a computer - click here to read our quick review. Using the Sigma Optimization Pro software you can then apply detailed autofocus microadjustments if you find your lens consistently mis-focuses on your camera (which can be something of an occupational hazard for SLR users). There's also an option to update the lens's firmware, if it should become necessary in the future.
|Sigma's USB Dock and Optimization Pro software lets you set AF microadjustments for four focal lengths each at four different focus distances.|
In principle this allows you to calibrate the lens's focusing specifically for your camera, and help you get the best possible results. Unfortunately, though, the software comes with limited documentation, and specifically no instructions on how you might set about determining the microadjustment values you need to set. So we wonder how many users will really be able to make the most of it.