The kit lenses you get with digital SLRs are good value, but they’re not always terribly good lenses. The problem is though, that the next step up from the camera maker’s own lens range is a big one. For example, Canon’s EF-S 17-85mm has a list price of £600 and Nikon’ 16-85mm is £550.

The Sigma 17-70mm offers a similarly useful step up, but at a much lower cost. The list price is £330, but careful shoppers could almost certainly knock around £80 off this, and end up with a lens which is optically superior, has a wider zoom range, better handling and a much shorter minimum focus distance.

This lens doesn’t offer a huge step forward in any particular respect, but it offers a modest advantage in many areas, and these add up to make it worth taking seriously as a kit lens replacement.

Most kit lenses have a focal range of 18-55mm, but the Sigma goes 1mm wider and 15mm longer. It’s not much, but it makes a difference.

It’s also around half a stop faster across its whole focal range (f2.8 at 17mm and f4.5 at 70mm). Again, it’s not much, but it’s definitely worth having.

And while most of us might not pay too much attention to a lens’s minimum focus distance, it’s an important factor here. Sigma calls this a ‘macro’ lens, which isn’t strictly accurate since true macro lenses offer a reproduction ratio of 1:1. Nevertheless, at its maximum focal length, the Sigma’s 0.2m minimum focus distance gives it a reproduction ratio of 2.3:1 and that is rather good. At this distance, the field of view is not much larger than the width of two keys on your computer keyboard, and there won’t be many ‘macro’ shots where you need to get a lot closer than this.

The Sigma 17-70mm’s appeal isn’t limited to its focal range, maximum aperture and close-up capability. It has subtler qualities too, which could be grouped loosely under ‘handling’.

First of all, it’s quite compact. It has a neat, cylindrical shape, and it looks right and balances up well even on the smallest D-SLR body. Second, the controls have a firm, precise feel with none of the play and looseness, which makes cheaper lenses feel, well, cheap. There’s a proper-sized manual focus ring at the front, with a clearly marked distance scale and a good, smooth action. And the front element of the lens doesn’t rotate during focussing, so you can use a petal-shaped hood without problems (you get one with the lens) as well as filters which rely on rotation for their effect (polarisers, graduated filters).

Most importantly of all, this lens offers a useful optical improvement over a typical kit lens. The resolution isn’t necessarily that much higher, since kit lenses will usually get near to the sensor’s maximum resolving power at some point in their aperture/focal length range anyway, so what you’ve got to look for instead is consistency. And here you get it. The edge performance drops away at full aperture at 17mm and 70mm, which drives the combined resolution figure at these settings down slightly, but elsewhere the resolution is consistently very good. This lens will give you sharp pictures in the centre of the frame at any aperture or focal length, and you only have to stop down to f5.6 for the edge definition to catch up. If anything, the Sigma is slightly weaker at its maximum focal length, but it’s not enough to make an obvious difference to your pictures and it’s still some way sharper than many kit lenses at full stretch.

There doesn’t seem to be much distortion, either. It’s visible in the test shots used for our resolution chart, but not so much in real-life photography. One possible explanation is that the distortion characteristics of some lenses may change according to the focus distance – everyday subjects will be much further away than photographic test charts.

What’s especially noticeable, though, is how little chromatic aberration there is. It’s there all right, at the edge of the frame, particularly at shorter focal lengths, but there’s much less than you’d expect from a typical kit lens. Chromatic aberration can be fixed using software, but it’s a tiresome process and it’s far better not to have any in the first place!

This is a very likeable lens. There’s nothing spectacular about its specifications, but it’s nicely designed, it handles well and it’s versatile. Most of all, it produces very good picture quality. It’s debatable whether it’s worth swapping an existing kit lens for this one, but if you bought your camera body-only, or if you just can’t get on with the kit lens you’ve got, then the Sigma 17-70mm is worth serious consideration.

Final Verdict The Sigma 17-70mm offers a useful step up from the average kit lens without costing a fortune. OVERALL

Our lens reviewer, and technical expert, Rod is a veritable photographic encyclopaedia. His illustrious CV has seen him write for many mags, websites and journals.