Sigma 20mm f/1.4 DG HSM | A

Offering an angle-of-view of 94.5° and an impressive aperture of f/1.4, Sigma’s latest prime, the 20mm f/1.4 DG HSM | A, is the widest ultra-fast full-frame DSLR lens ever. This unique combination makes it ideal for a range of subjects including events, astrophotography, landscapes and architecture. Available in Nikon, Canon and Sigma fits, it provides a 30mm equivalent focal length when mounted on an APS-C body. But can such a unique lens provide the optical excellence that has become associated with the brand’s Art series?

Sigma 20mm f/1.4 DG HSM | A

Sigma 20mm f/1.4 DG HSM | A

Image and build quality

As we’ve come to expect from Sigma’s Art line, the 20mm f/1.4 is built like a tank. Weighing 950g and measuring roughly 9cm in diameter by 13cm in length, it’s one of the largest wide-angle primes we’ve ever tested. Fitted with a brass mount and constructed of equal parts metal and Thermally Stable Composite, it’s reassuringly hefty for a professional lens. One slight downside is the bulbous front element and fixed petal hood, which has no thread, making it incompatible with most filters and mounts. This makes life difficult for landscape photographers.

The lens’ wide manual focusing ring feels pleasingly smooth in operation, while the barrel of the lens features a distance window and autofocus switch. Fitted with a Hyper Sonic Motor, the lens found focus silently and quickly on the Canon 5D MkIII we tested it on. Manual override of focusing is possible at any time by adjusting the focusing ring, while the lens can be fine-tuned using Sigma’s optional USB dock. Minimum focusing distance is an impressive 28cm. With nine rounded blades we found the bokeh produced by this prime at wider apertures to be attractive, while f/16 is its narrowest aperture. 

Featuring 15 elements in 11 groups, the complex 20mm f/1.4 features two Low Dispersion (F) and five Special Low Dispersion (SLD) elements to minimise chromatic aberration. It also employs two aspherical elements to reduce the distortion commonly found on wide-angle lenses, including one unique 59mm double aspherical element. This design yields some magnificent results. While unsurprisingly strong vignetting is present wide open, it improves quickly as the lens is stopped down. Users shooting with a crop sensor will be affected by this even less. Centre sharpness is very impressive at f/1.4, while even the edges of the frame are highly respectable for such a wide lens. Peak performance is around f/5.6-8 with commendable sharpness across the frame. Barrel distortion is noticeable, but considering the focal length is very well controlled, and could be corrected easily. Chromatic aberration is also minimised well.


Sigma has once again maintained its excellent form with the 20mm f/1.4 Art. Performing brilliantly even at its maximum aperture, it’s deserving of its professional asking price. The fixed lens hood is a bit of a peeve that will disappoint some landscape photographers, but this is an otherwise fantastic lens well suited to its target markets. Its closest rivals are Nikon’s 20mm f/1.8G and Canon’s 20mm f/2.8 USM. They may be cheaper, but they both have narrower apertures. If you’re looking for the perfect blend of wide-angle and fast aperture, look no further than this brilliant prime. 


  • Street price: £629 (As of July 2016)
  • Maximum aperture: f/1.4
  • Lens construction: 15 elements in 11 groups
  • Minimum focus distance: 27.6cm
  • Dimensions (DxL): 90.7x129.8mm
  • Weight: 950g
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This review was first published in the February 2016 issue of Practical Photography - download back issues here.