Overview

The Sigma 12-24mm Art is a full-frame compatible, constant f/4 aperture, autofocus lens. The build and finish quality matches that of all the Art lenses in the Sigma line up.
At 1150g and 112mm in length the lens really is a big lens. It certainly makes up for this bulk in looks. With its Fixed lens hood and curved bulb-like front element. The one downside to this curved front element is that conventional/traditional screw in filters doesn’t fit. This also means the lens cap slides over the front of the lens unlike the usual clip-on type.
Like all the Art lenses the zoom and focus rings operate very smoothly in the barrel, and the lens is Dust and splash proof. The lens overall feels very sturdy and the weight is largely due to the build quality.
 The autofocus motor has been updated for faster response, and as a result the auto focus system on the lens works well, and accurate. The lens doesn’t have Image Stabilisation, so you have to be careful hand holding the lens in low light situations.

Experience

The lens has a very wide focal length and you get the full 12mm of coverage. Shooting ultra-wide does mean you really have to watch out for your perspective distortion. The nature of 12mm Ultra-wide zoom lenses is they tend to have noticeable distortion and that’s also partly true for the Sigma 12-24mm f/4 HSM DG ART. The issue eases when zooming out. At 14mm, the barrel distortion is comparatively moderate and beyond 18mm it’s not noticeable at all.
The lens is sharp across the frame, with next to know softening on the edges of the frame. At 14mm + the performance is very good across the image field at all mainstream aperture settings. At 12mm f/4 there is some softness in the image corners of the frame but this is recovered at f/5.6. Overall the lens reaches its best clarity when stopped down to f5/6.
The lens creates a very strong and clear colour rendition, with great chromatic aberration control across frame. There is some vignetting on the edges of the frame. It’s largely undetectable, but there is a little light falloff at 12mm f/4 which is very moderate indeed for such a focal length. This being said, vignetting is very easily fixed in post processing so isn’t really an issue anyway.

Conclusion

Excellent sharpness and image quality of the lens is great throughout the range. And as a result the lens slots nicely into the Art range. As a wildlife photographer I very seldom reach for a wide angle lens but when I do, having a larger range proves very beneficial. This lens delivers fantastic clarity and detail under most light conditions handheld, but I would advise pairing it with a tripod in lower light.
Willam Steel, Sigma Ambassador