Introduction

Ease of Use

Weighing in at 370g / 13.1oz. and measuring 70mm x 74.4mm / 2.8in. x 2.9in., the all-metal bodied Sigma 20mm F2 DG DN is pretty light for such a premium full-frame lens.

Its overall size is well-suited to a camera like the Sony A1 that we tested it with, as shown in the product photos.

Even with the supplied hood attached, it is still fairly discrete for a 20mm lens.

The other 20mm lens that Sigma offer is the significantly faster but much, much bigger and heavier Sigma 20mm F1.4 DG HSM, which weighs in at more than 1kg.

The main lens that Sigma are targeting is the very similar Sony FE 20mm f/1.8 G, which is roughly the same size and weight but is crucially quite a lot more expensive.

The Sigma 20mm F2 DG DN is heavier than the comparable Tamron 20mm F/2.8 Di III OSD M1:2 lens, which only weighs 215g and is smaller too, measuring 64mm x 73mm.

Build quality is simply superb, far exceeding what you might expect from a mid-range prime lens.

Sigma have really gone to town on the new I series, so much so that they've explained in great detail just how much thought has gone into it.

It incorporates a brass bayonet mount that's supposedly more durable than a normal metal mount.

A rubber seal is incorporated into the lens mount's design to make it dust- and splash-resistant.

The Sigma 20mm F2 DG DN lens has a metal lens mount and it accepts 62mm filters via metal threads on the front of the lens.

The lens doesn't feature built-in optical image stabilisation, relying instead on the camera body's stabilisation system (if it has one).

The Sigma 20mm F2 DG DN lens has an adequately sized, ridged motor-assisted focus ring that is very nicely damped. Manual focusing is possible by using the focus mode switch to toggle between AF and MF.

There are no hard stops at either end of the range, making it a little more difficult to set focus at infinity. Polariser users should be pleased that the 62mm filter thread doesn't rotate on focus.

The manual focusing ring is positioned a little too closely to the lens hood when it's fitted, though, so much so that my right thumb rubbed along the edge of the hood as I rotated the focusing ring. A minor detail, maybe, but still of some importance on a lens where attention to detail is the defining characteristic.

The Sigma 20mm F2 DG DN lens utilises a stepping motor which produces quiet, almost silent, smooth focusing, making it well-suited to shooting both stills and video, with the overall lens length remaining constant during focusing.

When it comes to auto-focusing, it proved to be a quick performer on the Sony A1 camera that we tested it with.

We didn't experience very much "hunting", either in good or bad light, with the lens accurately focusing almost all of the time.

Sony's near flawless Eye AF works perfectly with this lens, quickly locking onto and tracking the subject's eye despite the wide-angle view, and it fully supports Sony's DMF and AF+MF shooting modes.

The Sigma 20mm F2 DG DN lens features an aperture ring that has 1/3EV stops ranging from f/2 to f/22 and an Auto setting if you prefer to set the aperture via the camera body.

Sadly there's no Click switch on the lens barrel that lets you de-click it for silent operation during movie recording.

The Sigma 20mm F2 DG DN lens isn't supplied with a lens case, but it does come with a very good quality, hybrid plastic and metal, petal-shaped lens hood (LH656-02) that continues the ribbed texture of the lens barrel, and also an innovative magnetic metal lens cap (LCF62-01M), in addition to a normal plastic cap.

This dedicated metal cap clips to the front surface of the lens magnetically, and there's even an optional magnetic metal lens cap holder (CH-11) that can be clipped to a bag or a belt.

Note that the magnetic lens cap can't be used with filters, though, and is also quite awkward to use when the lens hood is fitted.

Focal Range

The 20mm focal length provides an angle of view of 94.5 degrees on a full-frame camera.

Chromatic Aberrations

Chromatic aberrations, typically seen as blue or purple fringes along contrasty edges, were somewhat apparent in our test shots, appearing in very high contrast areas. The examples below show the worst-case scenario.

Light Fall-off

With the lens set to its maximum aperture of f/2, there is very obvious light fall-off in the corners, requiring you to stop down by at least 3 f-stops to completely prevent it.

Distortion

There's a lot of distortion evident in both the JPEG and RAW files which you'll need to correct in post-processing. Alternatively, most Sony Alpha cameras can automatically and successfully apply Lens Distortion corrections to the JPEG files, but not to the RAWs.

JPEG

Raw

Sunstars

The Sigma 20mm F2 DG DN is capable of producing quite nice sunstars when stopped-down to f/16 and f/22, as shown below.

The lens is susceptible to flare when shooting directly into the sun, though, even with the supplied lens hood fitted.

Macro

The Sigma 20mm F2 DG DN isn't really a macro lens, offering a minimum focusing distance of 22cm / 8.7in. and a maximum magnification ratio of 1:6.7. The following examples demonstrate how close you can get to your subject.

Bokeh

Bokeh is a word used for the out-of-focus areas of a photograph, and is usually described in qualitative terms, such as smooth / creamy / harsh etc.

In the 20mm F2 DG DN lens, Sigma have employed an iris diaphragm with 9 circular blades, which has resulted in appealing bokeh for what is after all a wide-angle lens.

We do realise, however, that bokeh evaluation is subjective, so we've included several examples below for your perusal, all shot wide-open at f/2.

Sharpness

In order to show you how sharp this lens is, we are providing 100% crops on the following page.