This 70-300mm is one of Sigma’s DG lenses, which means it’s been optimised for digital SLRs with smaller sensors but can also be used on 35mm film cameras and full-frame digital SLRs. It offers a good telephoto range even on a full-frame camera, but on an APS-C digital SLR it equates to approximately 110-470mm.

And at that kind of magnification, you’re going to be glad of Sigma’s Optical Stabiliser (OS) technology. Like other lens-based systems, it moves an internal lens element to counter any camera movement, and the advantage of this over sensor-shift systems is that the image is stabilised in the viewfinder while you’re composing it. This is half the battle with super long-range shots, where simply keeping the subject in the frame is hard enough.

Our test charts suggest, though, that the 70-300mm delivers its best sharpness with the OS switched off and the camera mounted on a tripod. With the OS switched on, the centre lens element had a disconcerting wobble (visible by looking through the front element), but this went away when the camera was powered up and the autofocus activated. For handheld shooting, though, the optical stabilisation is a must.

The figures show typical performance characteristics for a telephoto zoom, with the best sharpness found at short and medium focal lengths and a reduction in sharpness at full zoom. The Sigma did prove rather better than average in all three respects, though, and the main drop in performance at 300mm was wide open at f5.6. At f8 and f11 it rallied to produce quite good results for a lens of this focal length.

The test charts and our real-world tests showed that it wasn’t just the definiton which was above average. Most long-range telephotos show a marked loss of contrast at their maximum focal length coupled with a big increase in chromatic aberration, but neither proved a problem with this Sigma.

That’s not to say it doesn’t need to be used with care. Like any long range zoom, it takes a certain amount of skill and practice to get the best from this lens. Even in good light, it’s advisable to use a higher ISO than you would normally. The optical stabilisation does indeed help cut camera shake, but it’s even better if you can reduce the likelihood of it happening. In ideal conditions, you can get sharp results at pretty slow shutter speeds, but if the wind’s blowing, if you’re on uneven ground or you’ve got to shoot in a hurry, the higher the shutter speed the better. A higher ISO will also let you use smaller lens apertures. You don’t really want to be using this lens wide open at 300mm if you can avoid it, and there’s very little depth of field at these focal lengths anyway, so smaller apertures will improve your success rate.

And good though it is, the Sigma 70-300mm needs to be weighed up carefully against the alternatives. For a start, budget 55-200mm ‘digital’ lenses don’t have the same reach, but they’re a lot cheaper and, because they’re designed for the smaller sensors of digital SLRs, they’re lighter and easier to handle. Or, if you just want the extra focal length on the off-chance, an 18-250mm superzoom lens is a lot more convenient. You won’t get the same optical quality at long range as the Sigma 70-300mm provides, but you will be able to fit just one lens on the camera rather than having to carry around two lenses and keep changing them.

Where the Sigma 70-300mm scores, though, is for wildlife or sports photography where you know you’re going to be some distance from your subject and outright flexibility is less important than optical performance and long-range zooming. Here, the Sigma delivers good performance at a very reasonable price.

Final Verdict Like all telephoto zooms, the Sigma loses a little definition at its maximum focal length, but the overall sharpness is above average, the contrast is good and there’s very little chromatic aberration or distortion, even at full zoom. 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.