This is without doubt one of the finest-quality optics we've yet tested, capturing incredibly sharp images with no evidence of distortion or vignetting. The 16 elements used in its construction include three SLD (Special Low Dispersion) and FLD ('F' Low Dispersion) glass elements, as well as an aspherical lens, to minimise aberrations, with the fast maximum aperture and nine rounded iris blades producing very attractive bokeh. Contrast is excellent too, with Sigma’s Super Multi-Layer Coating working well to prevent flare and ghosting. Canon fittings are compatible with Canon's Lens Aberration Correction function, while an electromagnetic diaphragm mechanism for precise iris control is found in the Nikon-fit version.
Build quality is of the highest standard too, with the barrel feeling very solid and the mount made of hard-wearing brass. A focus window provides distance information, while the wide focus ring handles manual-focusing adjustments smoothly. An AF/Manual focus switch is found to the side, but the lens can be manually focused while it's still engaged should you so wish to fine-tune AF. You'll probably find this is rare though, as the HSM system provides extremely responsive and quiet AF.
Sigma offers some outstanding standard primes in its Art series and this 40mm f/1.4 is the best we've yet tested in terms of image quality. However, it's a beast to carry and expensive, so we'd say many will find the (£579) 50mm f/1.4 a more practical option.
Guide Price: £1,099
Lens construction: 16 elements in 12 groups
Number of diaphragm blades: Nine (rounded)
Angle of view: 56.8°
Minimum aperture: f/16
Minimum focusing distance: 40cm
Maximum magnification: 0.15x
Filter Size: 82mm
AF Fittings: Canon, Nikon, Sigma, Sony E, L-mount
Supplied accessories: Case, hood, front & rear lens caps