This digital-only lens boasts excellent performance, Optical Stabilisation and a rock bottom price tag - so is there anything not to like?
The most obvious difference between this lens and Sigma’s previous 17-70mm f/2.8-4 zoom is the addition of optical stabilisation and the move from Super Low Dispersion (SLD) to Extraordinary Low Dispersion (ELD) glass, now used for the rear element rather than the element immediately behind the aperture. A third aspherical profile has also been added to the design and the lens is now additionally available for Pentax and Sony cameras as well as Canon, Nikon and Sigma.
As is so often the case these days, the macro label does not refer to a true macro capability (1:1) but it does at least provide a healthy reproduction ratio that is approaching half life-size. Given the smaller dimensions of an APS-C sensor, the reduced magnification looks similar to true macro on a full-frame camera.
Handling is generally good but there is one serious niggle, which is that the focusing ring rotates in AF mode despite the use of internal focusing. This would not be quite so serious were it not for the fact that the zoom’s compact size and the forward location of its focusing ring means that, for me at least, it is almost impossible to avoid gripping the ring when holding the lens securely.
In MF mode the focusing ring is a shade loose, especially in comparison with the noticeably heavy action of the zoom ring. There is no opportunity to apply manual focusing adjustments when the lens is set to AF mode.
Power for the OS system comes from the camera and is therefore an additional drain on the battery: this is worth remembering if you find that the camera’s battery is running down and you need to conserve as much energy as possible. It also means that the lens is active in OS mode for as long as the viewfinder and LCD panel are active. Sigma sensibly warns against removing the lens when OS is energised, as this may cause damage to the mechanism.
MTF testing reveals this to be a very impressive lens that exceeds 0.3 cycles-per-pixel from wide-open to f/11 across the full 4.1x zoom range, with very little chromatic aberration seen. Stopping the lens right down (not shown on the MTF graph) wrecks the resolution and should be avoided if possible.
Overall it is hard to believe that this lens is for real: it has stunning resolution, optical stabilisation, a more-than-four-times zoom range and can be purchased for not much over £300. Fantastic!