Best zoom lens upgrade for canon dslrs: 10 tested

Sigma 24-70mm f/2.8 EX DG IF HSM - £640

Here's another money-saving opportunity in the rather squat shape of Sigma's fast, constant-aperture, full-frame zoom. It's less than two-thirds the price of the competing Canon 24-70mm lens and, like the Canon, lacks stabilisation but boasts super-fast, near-silent ring-type ultrasonic autofocus.

The Sigma is shorter than the Canon but has a wider circumference to accommodate its large front element, reflected by its huge, 82mm filter thread.

Despite the oversized front element, vignetting is quite pronounced on a full-frame camera, especially at the 24mm wide-angle zoom setting, even when the aperture is reduced by two stops to f/5.6. It's less of an issue on APS-C cameras, where the image circle is cropped and vignetting is barely noticeable.

Sharpness proved a tad disappointing at the largest aperture, especially at the wide-angle end of the zoom range. At midrange and telephoto lengths, we still needed to reduce the aperture to f/5.6 for good sharpness across the whole frame.

But from a handling perspective, the lens feels solid and well built, and more conventional than its Canon equivalent in that its physical length increases towards the telephoto end of the zoom range.