Conclusion

The Sigma 12-24mm F4 DG HSM Art is a fantastic ultra-wide-angle zoom lens that significantly undercuts the price of its main rivals whilst offering almost comparable image and build quality. 

Image quality is excellent. Chromatic aberrations are well controlled, bokeh is pretty impressive despite the slow f/4 aperture and the wide-angle nature of the lens, and the Super Multi-Layer coating successfully prevents contrast loss attributable to flare. The only real optical issues are some vignetting, particularly at 12mm, obvious barrel distortion at the 12mm wide-angle focal length, and a slight lack of edge sharpness when shooting wide-open at f/4 throughout the zoom range.

As with all the other recent Art lenses that we've tested, the Sigma 12-24mm F4 DG HSM Art's build quality is reassuringly excellent, although it's also one of the heaviest wide-angle zooms that we've ever tested. Auto-focusing is quiet and quick, with the ability to manually override it and focus manually if required proving a nice touch. We would have liked a wider focusing ring though.

All in all, the Sigma 12-24mm F4 DG HSM Art is an excellent alternative to the likes of the Canon EF 11-24mm f/4L USM, Nikon AF-S NIKKOR 14-24mm F2.8G ED and the Tamron 15-30mm f/2.8 Di VC USD lenses.

Ratings (out of 5)
Design	4.5
Features	4.5
Ease-of-use	4.5
Image quality	4.5
Value for money	5