Scoring 17 P-Mpix for sharpness, resolution on the Sigma 12-24mm f/4 A equals the best performance of Nikon’s ultra-wide 14-24mm, and is only a little behind the class-leading Sigma 24-35mm f/2 A. At f/4, the Sigma 12-24mm f/4 A offers uniform resolution of around 70% acutance in the field between 12 and 20mm, with good center sharpness and slightly softer corners at 24mm f/4. It hits peak sharpness of over 70% acutance at f/8, and using the mid apertures (f/8 and f/11), it’s very close to uniform at all focal lengths. Using the minimum f/22 aperture for long depth-of-field shots, the Sigma ultra-wide zoom offers good uniform sharpness at around 60% acutance.
Conclusion from DxOMark:
Sigma’s Art range of high-performance, super-sharp optics, designed to maximize the high-resolution sensor potential of DSLRs such as the D800, have gained a formidable reputation for quality and value. The Sigma 12-24mm f/4 A isn’t quite on par with the sharpness potential we’ve seen with some of Sigma’s wide-angle Art prime lenses, such as the 24mm f/1.4 A or 35mm f/1.4 A, but for a wide-angle zoom lens, it still performs exceptionally well on the D800. It delivers great performance across the board, with excellent sharpness that rivals the own-brand Nikon 14-24mm f/2.8G alternative; best in-class distortion control with minimal curvature at either end of the zoom; and well-controled vignetting and chromatic aberration. Priced between the Nikon 14-24mm f/2.8G and the Tamron 15-30mm f/2.8, it’s a good value, too. The Tamron offers a couple of extra features, such as the faster f/2.8 maximum aperture and image stabilization to boost its low-light credentials, but the Sigma’s wider 12mm focal length will have a different appeal for many full-frame landscape and architectural photographers.
Read the full review at DxOMark.