Photo answers review
Photo answers rating 
Optical image stabilisation is a big selling point for cameras at the moment. If it’s not built into the camera already, in the form of a moving sensor, then it’s readily available in the lens instead. Sigma’s popular 70-300mm telephoto is the latest lens to join the stabilised ranks but at a substantial premium over its £180 APO sister lens. Suitable for APS-C and full-frame cameras, this version boasts Sigma’s own OS (Optical Stabiliser) system. This detects vibrations caused by handholding the camera and reacts to it by shifting a group of elements within the lens. This allows you to get away with using slower shutter speeds than previously possible. In fact, Sigma boldly states that you can shoot with shutter speeds up to 4 stops below the usual. This equates to 1/20sec shutter at 300mm (on a full-frame camera) instead of 1/300sec. It’s an impressive claim.
Build qualityConsidering the price point, this lens is pretty solid. It rattles a bit but has a reassuring weight and doesn’t feel plasticky in the hand. There’s a metal mount, and a wide zoom grip, which is easy to handle. The zoom is stiff enough to stay put when hung around your neck, and the autofocus is swift enough for most purposes. The AF ring turns in when the camera focuses though, so make sure your fingers are clear of it. There’s a built-in optical stabilisation system and a lens hood included in the box. It’s only f/5.6 at the long end though.
Image qualityIt’s clearly not a professional lens, but the performance is admirable. Images are crisp in the 70-200mm zoom range, and performance at f/5.6 is impressive. In fact, we found little benefit by stopping down to f/8 or f/11. Above 200mm the image becomes a little fuzzy, but this is typical of a lens in this class. As expected, image clarity was best with our full-frame test camera. Edge-to-edge sharpness and vignetting were well controlled too. Our APS-C camera showed some extra softness, but the results were still very good. Remember, as with many telephoto lenses, camera shake is the biggest culprit for softness in images and not the optics.
Optical stabilisationTap the shutter, and you’ll instantly see the OS system snap into action. Camera movements appear dampened through the viewfinder, making manual focusing much easier. Comparing the result with and without OS proved its effectiveness. With extra care taken to hold the camera still it can live up to the 4-stop anti-shake claim. At the extremes, only a few shots were critically sharp, but about half were useable. Faster shutter speeds, just a stop or 2 below the recommended speed, achieved a better hit rate, but also showed that the system is not foolproof. The same care needs to be taken with OS on as it does when off. A slight wobble or gust of wind can still blur the image. In the field we had most success using the ‘correct’ shutter speeds and not relying on the OS.
Overall verdictSigma’s latest 70-300mm has entered a very crowded spot of the market, so competition is fierce. However, it is the cheapest full-frame stabilised lens by around £100. Image quality is on a par with the rest, so it’s a tempting option. The question is, do you really need OS? Sure, it helps make up for the poor light gathering capabilities, but it won’t help you with fast moving subjects. Autofocus will struggle when light is scarce too, compared to a wide aperture telephoto lens. If you’re into landscapes then consider getting the normal Sigma 70-300mm APO lens instead, and spend the remaining £140 on a decent tripod – it’s a more versatile combination. Budding sports and reportage photographers should save up for the incredible £660 Sigma 70-200mm f/2.8 too. However, if you need a lightweight performer with the reassurance of stabilisation system, then this lens offers unbeatable value.
SpecificationStreet price: £320
Max. aperture: f/4-f/5.6
Min. aperture: f/22-f/32
Aperture blades: 9 (rounded)
Construction: 16 elements in 11 groups
Closes focus: 150cm
Filter size: 62mm
Weight: 610g
Size (DxL): 76.5x126mm