Sigma has created a world first with its latest wideangle prime lens, but how valuable is it in the company’s line-up? Michael Topham investigates
Sigma 20mm f/1.4 DG HSM | A Review – Features
If you’re wondering why a 20mm f/1.4 lens has never been manufactured before, it’s because of the technical difficulties that are imposed by engineering such a large double aspherical element. Sigma has managed to overcome this hurdle by turning to its experienced team of engineers who have used the latest advances in technology to successfully create a large double-aspherical lens that measures an impressive 59mm in diameter. By uniting this large aspherical lens with a second aspherical lens towards the rear, we’re told that it controls distortion remarkably well – a claim that we intend to investigate in this test.
The construction of the lens features 15 glass elements arranged in 11 groups, with two of these elements being the ‘F’ low-dispersion (FLD) type and five being the special low dispersion (SLD) variety. This low-dispersion glass is used to curtail chromatic aberrations, which are well known for being an issue in large-aperture ultra-wideangle lenses. To prevent flare and ghosting presenting problems when shooting towards the light, Sigma has employed its Super Multi-Layer Coatings and a permanently fixed petal-shaped lens hood at the front.
The lens’s nine-bladed aperture diaphragm offers settings from f/1.4 to f/16, and set to its maximum aperture it provides an attractive rendition of out-of-focus backgrounds with pleasing circular bokeh in the highlights. To ensure the lens operates as smoothly and as quietly as possible, the lens features Sigma’s Hyper Sonic Motor (HSM) that, in addition to driving the autofocus system, offers full-time manual focusing. This allows users to adjust the focus manually at any time without having to flick the AF/MF switch to manual first.
Like all lenses released by Sigma in recent times, it will be initially manufactured in three different lens mounts to cater for Canon, Nikon and Sigma users. The size and weight imply that it’s going to be a lens that feels at its best paired with full-frame DSLRs, but there’s nothing to suggest it can’t be used with APS-C DSLRs. Coupled to an APS-C DSLR with a 1.5x crop factor, it behaves like a 30mm f/1.4, whereas on Canon APS-C DSLRs it’s equivalent to 32mm.
Other noteworthy features include a minimum focusing distance of 27.6cm, a maximum magnification ratio of 1:7.1 and full compatibility with Sigma’s USB docking device, allowing users to update firmware and refine the focus settings manually using the manufacturer’s Optimization Pro software.
As part of the boxed contents there’s a rear cap and a sizeable front plastic cap, which has a slim felt-like lining on the inside to create a tight fit. For photographers who’d prefer a more robust lens cap, Sigma also produces a metal lens cap (LC907-02) for £30.