Sigma 20mm F/1.4 DG DN Art Lens Review

Identical in style and control layout to the previously tested Sigma 24mm f/1.4 DG DN Art, the Sigma 20mm f/1.4 DG DN Art lens stretches that ultra-wide field of view just a little bit further. That 4mm difference though does make a very big difference to how the images look, how the lens handles and potentially makes more challenges for the lens designer as well as the photographer. Everything that has been said about getting in close with a 24mm lens can be repeated, but even more so with the 20mm. Once mastered, though, there is huge potential for dramatic, intense and very involved image making. This can apply, for example, to street photography, where the necessity to get in close means the photographer becomes personally immersed in the surrounding events. So, armed with the 42MP Full Frame Sony A7R III, let's take the new lens and duly immerse ourselves in the reviewing process, assessing the performance in the technical tests as well as the photographic potential in the wider world.

Sigma 20mm F/1.4 DG DN Art Handling and Features

Weighing in at 635g (L mount) or 630g (FE mount) the lens is not overly heavy, but is quite bulky, measuring 87.8mm in diameter and 111.2mm long (L Mount) or 113.2mm long (FE mount). However, it balances well on the camera body. There is a provided petal lens hood that bayonets cleanly and smoothly into place, a locking catch ensuring that it does not become detached in use. Within the bayonet fit for the hood is a conventional 82mm filter thread.

Just behind the hood, the lens is shaped with a lip that is intended to retain a lens heating collar, preventing it from slipping into the field of view. It may well impinge upon the wide electronic focusing ring, but if required there is an MFL (manual focus lock) switch that disables the ring. The lens is clearly designed to be astophotography-friendly. The focusing ring is as smooth as expected and has a slightly heavier feel than many, but this does mean that dislodging the point of focus becomes less likely. All the usual Sony focusing modes are supported. Focusing is down to 23cm (0.75 feet) for a maximum magnification of 1:6.1 – this is usefully close. AF is driven by a stepping motor and is virtually silent, fast and accurate. This will be helpful for videographers as well as stills photographers.

There are various switches around the lens barrel. The click off/on switch controls the click stops on the aperture ring. The MFL switch, as mentioned, disables the manual focus ring. The AFL button locks the AF point. The AF/MF switch is self-explanatory. On the opposite side of the lens barrel is a lock switch that controls the aperture ring. The ring can either be locked into the A setting or locked out of it. This means that when using the A setting and letting the camera control the aperture the ring cannot be accidentally moved to a value. Equally, if the aperture ring is being used then it cannot be inadvertently switched to A. The aperture ring itself is very well engineered and the one-third of a stop click stops engage cleanly and precisely.

The lens mount is beautifully made using brass and also incorporates a gelatin filter slot. There is a template provided that enables filters to be cut to shape. Overall construction quality is excellent, with both Aluminium and Thermally Stable Composite being used. The latter has the same coefficient of expansion as the Aluminium, so can be used alongside it to help reduce weight.

Optical construction is 17 elements in 15 groups, including 2 SLD (Super Low Dispersion) and 3 Aspherical, including the largest double-sided aspherical element that Sigma has so far manufactured. The diaphragm comprises 11 blades, which promises smooth bokeh. The front element is water and oil repellent and the whole lens is dust and splashproof. The instruction manual does quantify the water resistance as being able to resist light rain, but not a thorough soaking. Anti-reflection measures are aided by super multi-layer coating and nanoporous coating.

The L mount version of the lens is compatible with the Sigma USB dock UD-11.

The beauty of the ultra-wide lens is the way we can become immersed in our subject, with a close point of view that gives us the dramatic perspective that we expect. Without this thoughtful and confident use of the lens results could be very bland, from a compositional point of view, so spending some time exploring the characteristics of the lens is time well spent. Small changes in viewpoint and distance can make big changes to the look of images. This new Sigma lens is a great example of the 20mm lens and of the lens makers' art.