The Sigma 12-24mm f/4 DG HSM Art is an ultra-wide zoom lens that caters to photographers who love to shoot landscapes, architecture or interiors.
It has a constant maximum aperture of f/4 through its entire focal range of 12mm to 24mm, for low-light situations.
The lens features elements, made from Sigma's "F" low-dispersion glass, that are combined with aspherical lenses, to help minimise distortion and chromatic aberration.
To lower the effects of flare and ghosting, Sigma applied its Super Multi-Layer coatings to the lens and armed it with a built-in petal-shaped lens hood at the front.
The lens also has a nine-blade rounded diaphragm that creates nice, circular out-of-focus highlights. The build of the lens is pretty solid, but it is quite a heavy lens at over 1kg.
If you use a Nikon DX DSLR camera that has a crop factor of 1.5x, the resulting focal range will be 18-36mm. For Canon APS-C DSLR cameras, the lens will have a resulting focal length of 19-38mm.
For this review, I used the lens with my old but trusty workhorse, the Canon EOS 7D.
PRICE: $2,288 (Canon mount, version tested; Nikon mount, Sigma mount)
FOCAL LENGTH: 12mm to 24mm
FOCUSING RANGE: 0.24m to infinity
MAXIMUM APERTURE: f/4
MINIMUM APERTURE: f/22
VALUE FOR MONEY: 5/5
The lens uses Sigma's Hyper Sonic Motor (HSM) to power the autofocusing (AF) system. But there is a manual focusing ring that lets you focus manually any time without switching to manual focus (MF) using the AF/MF switch on the lens.
The AF is accurate, taking around 1sec to secure a focus, even in dim lighting conditions.
Image quality is simply superb. At f/4, the images shot are pretty sharp at the centre of the frame over the entire focal range.
However, corner sharpness is slightly lacking, especially from 20mm to 24mm.
When the aperture is stepped down to f/5.6, the corner sharpness improves. But it still looks a tad soft from 20mm to 24mm.
I discovered that, for optimal edge-to-edge sharpness across the entire focal range, keeping to f/8 will yield favourable results.
That said, I am still really happy with all the images shot with any aperture setting or focal length.
And the best part about this lens is its affordable price.
Compared with Canon's EF 11-24mm f/4L USM ($4,719), which has similar focal range and aperture size, the Sigma lens costs less than half as much and yet delivers really crisp images.
•Verdict: The Sigma 12-24mm f/4 DG HSM Art is a superb value-for-money ultra-wide angle lens that landscape and architectural photographers will find very useful.