Studio Tests

The Sigma 18-35mm F1.8 DC HSM turns in an exceptional performance in our studio tests, in essence matching a selection of high quality primes. It's remarkably sharp, even wide open, and both chromatic aberration and vignetting are relatively low. Distortion is kept pretty well under control too. Overall this is very, very impressive indeed.

Sharpness The 18-35mm is remarkably sharp even wide open at F1.8, and in the wider half of its range (18-24mm), there's no measurable increase on stopping down (i.e. the lens is effectively diffraction limited). At the longer end (28-35mm) there's a slight improvement in sharpness on stopping down to F4, but in practice it's unlikely to be especially noticeable. For an F1.8 zoom, this is little short of astonishing.
Chromatic Aberration Lateral chromatic aberration is pretty low. The graphs indicate a little green/magenta fringing at wideangle, and moderately strong blue/yellow fringing in the middle of the range (note though that this tends to be visually less intrusive). At the long end, chromatic aberration is essentially nonexistent.
Vignetting Vignetting is remarkably low for such a fast lens, reaching just 1.3 stops wide open at all focal lengths. It also essentially disappears by F2.8. Overall it's unlikely ever to be problematic in real-world use.
Distortion Distortion is kept reasonably well under control - it certainly doesn't exceed what we'd expect for this kind of lens. There's visible barrel distortion at wideangle, turning to pincushion distortion at the long end, but no more than you'd get from any other premium standard zoom.

Lens test data compared

To get a bit more perspective on just how good the 18-35mm is, let's compare it to a couple of benchmark lenses, using the comparison tool in our lens data widget. Click on the images below to open side-by-side comparisons in a new window or tab.

Compared to Sigma 35mm F1.4 DG HSM

The Sigma 35mm F1.4 DG HSM impressed us hugely when we reviewed it at the end of last year, and is probably the sharpest 35mm F1.4 prime on the market. When tested on the same camera, the zoom may be just fractionally less sharp at large apertures, but you probably wouldn't see any difference in real world shooting. The zoom also has slightly higher vignetting and distortion, but lower chromatic aberration. From this data, you'd be hard pushed to see any meaningful differences between the two in side-by-side shooting. Remember this is the 18-35mm's weakest focal length.

Compared to Tamron 24-70mm F2.8 Di VC USD

The Tamron 24-70mm F2.8 Di VC USD is probably the best value fast 'normal' zoom for full frame cameras, and like the Sigma 35mm F1.4, we had no hesitation in awarding it a Gold Award in our recent review. Not only does it offer built-in image stabilization, optically it comes as near as makes no difference to its Canon and Nikon counterparts, which are both much more expensive.

These lenses can be compared in several different ways, but its clear that regardless of whether we look at them them both tested on the same camera body, or at how the Sigma on APS-C compares to the Tamron on full frame, the 18-35mm easily holds its own in these studio tests.

Compared to Canon EF-S 17-55mm f/2.8 IS USM

Canon's EF-S 17-55mm f/2.8 IS USM is a highly regarded fast normal zoom for APS-C SLRs, and in comparison to the Sigma, offers an extended zoom range and built-in image stabilization, which makes it a very flexible lens indeed. But when we compare the two purely in terms of image quality, it's clear that not only is the Sigma noticeably sharper than the Canon when both are set to F2.8, it's actually sharper at F1.8 than the Canon is at F2.8. In all other respects, it matches up well too.