Sigma don’t have much competition in the wide zoom market, with decades of experience and specialist knowledge gleaned since their early lenses and the 1979 Zoom Gamma. Following up classics like the 15-30mm EX with the DC 8-16mm, 10-20mm and full-frame 12-24mm, their expertise in the field is well established.

The 12-24’s most recent refesh, launched at the beginning of 2011, is a significant update of the pioneering lens, featuring 17 elements in 13 groups (vs 16 in 12 on the original), four aspherical elements and four FLD elements.
SigmaUser has previously featured a comparison of the 12-24 and 12-24Mk II from contributor Pete Bridgwood, and now freelance journalist Richard Kilpatrick has taken the latest revision out with Nikon’s new D600 body.
You’d be forgiven for thinking the Mk II was little more than a marketing tweak – in fact, it’s a new optical forumula, new glass, new physical design – in short, it’s a wholly new lens. It weighs rougly 70g more than its predecessor, and loses the ability to use a rear-mounted gelatin filter; for APS-C users it’s possible to use an 82mm filter in the slip-on lens cap, thanks to a detachable conventional cap on that collar, but for full-frame users the integrated petal hood is needed to avoid vignetting and digital post-processing will be the best solution.
The new formula means that a slightly different maximum magnification applies, 1:6.4 vs 1:7.1, though in other regards the 28cm minimum focus, 6-blade diaphragm and F22 minimum aperture remain. Both variants are F4.5-5.6 variable aperture.
 

Sigma 12-24mm and 12-24mm HSM Mk II differences.
Above – the Sigma 12-24mm 16 elements in 12 groups.	MTF chart for the original 12-24.
Above – the 12-24mm HSM Mk II with 17 elements in 13 groups.	MTF chart for the 12-24 Mk II, indicating a higher resolution for a greater area of the image circle and a closer relationship between Sagittal and Meridional performance.

 
The 28cm minimum focus makes it a delightful lens to just walk around and look at the world through.
 

 
For commercial and illustrative work, the 12-24 has a strong application in architecture and interiors. Thanks to the high ISO capability of most modern DSLRs, a working aperture around F8 will still allow hand-held shots for the estate agency and insurance fields, where camera operators may not be skilled photographers. There is slight disortion visible, but with lens correction in camera or in applications like Lightroom, it is easily and quickly corrected. Vignetting manifests itself below F7.1, but again, is easily controlled and for many wider landscapes or exterior shots, lends a natural framing to the image – it’s not obtrusive.
 

 
Flare, as with any superwide zoom with a front lement like this (the 122° angle of view making it somewhat hard to avoid the sun if it’s anywhere near your subject), is perhaps the most intrusive flaw you will encounter. As in cinematography, it has become commonplace to retain flare as a sign of authenticity; the viewer is familiar with the behaviour of lenses and recording media, and expects it. Nevertheless, sometimes it can be obtrusive if not spotted when composing the image.
 

 
The great benefit of the 12-24 is working with it at 12mm and being able to capture expanses of design, architecture, free of converging or distorted lines. In this case, the courtyard of Calke Abbey is captured, working with the in-camera levels, and only slight processing to enhance the contrast of the frame and bring more texture to the sky is needed. The flare is knowingly captured here, and of course, could be avoided. The lack of distortion in the captured image makes simple convergence corrections easy and natural, if required, allowing some flexibility in composition whilst still aiming for a straight output file. Vignetting has not been an issue here, though the contrast of the sunlit walls would mask it somewhat regardless.
 

 
These exterior shots show the flexibility between 12mm and 24mm.
 

 

 
Where the original 12-24 has a reputation based on compromise – it delivered something new to the market, and remains unique – the Mk II is a much stronger performer optically. With a growing market of small, manageable full-frame DSLRs it will come into its own as a creative, inspiring lens for enthusiasts whilst delivering the resolution and quality that suits the latest generation of sensors – even on the D800E, the only optical correction needed was minor defringing, the bokeh remains appealing and the sharpness in the centre is impressive even wide open. Just as with the SD1, I consider the 8-16mm an essential – for full-frame users, the 12-24mm HSM Mk II will provide that extra width over the kit lens and in most cases, a significant improvement in quality, and will take you to the very limits of rectilinear wide-angle performance – beyond, there by fisheyes.
 
¹ Dig hard enough, and you will find some which match or approach it, but with a lot of expense or tweaking. Nikon’s 13mm – not a Zoom – and a rangefinder 12mm Voigtlander. For all intents and purposes, Sigma’s 12-24 is the widest rectilinear lens and one of the widest zooms you’ll get on a full-frame, and it requires no messing about to use it to full potential on the latest FX Nikon bodies, for example. Go to 14mm and you’ll get speed from other marques, but at a price.