Who’d have thought it? Not so long ago we were in the grip of zoom fever, but now prime lenses are back in fashion… the faster the better and even, with quite a number of models, good old manual focusing. Of course, a lot of the current activity is being generated by the rise and rise of the mirrorless systems, but even with the D-SLR brands essentially whittled down to just three, there’s still a lot happening here too.

Never one to sit still for very long, not surprisingly, Sigma is doing its bit in both categories, but it’s the Art Series lenses for D-SLRs which are really on target right now. The line-up started with a classic 35mm prime, following by a standard 50mm and, more recently, a 24mm wide-angle. All have a maximum aperture of f1.4. Additionally, you can have the 24mm and 35mm focal lengths (and all points in between) in the first ‘DG’ Art Series zoom, but the main penalty is the loss of a stop of lens speed. Sigma’s ‘DG’ designation indicates a lens primarily designed for use with full-35mm sensors while ‘DC’ indicates an ‘APS-C’ format model.

The rationale behind Sigma’s Art lenses is not just a purity of purpose derived from the combination of focal length and maximum aperture, but also a purity of design which translates into superior optical performance. Consequently, the main competition – in terms of the independent lens makers – is coming from Zeiss which is charging rather a lot more for manual focus lenses versus the autofocus Art models, but Sigma is also holding its own against rival designs from both Canon and Nikon.

Look And Feel
The Sigma Art lens experience starts with the physical aspects of the design and construction. The styling is neither overtly classical nor contemporary, but rather elegantly understated with a matte black finish, a large and flush-fitting manual focusing collar and the small, discreet ‘A’ badge inset into one side of the barrel. At 665 grams, the 24mm model tested here has a nicely weighty ‘heft’ which suggests a solid construction, but the exterior also screams precision, particularly evident in the fineness of the tolerances where any two components meet. The focusing distance scale is inset, marked in both meters and feet, and accompanied by a depth-of-field scale for f8.0 and f16. The focusing collar has a ribbed rubber grip, and the control itself is mechanical so it’s properly weighted and allows for precise fine-tuning. The rear section of the main barrel is also ribbed. Interestingly, on the base of the barrel are engraved the numbers ‘015’ which indicate the year this particular model was introduced.

The barrel construction is a mixture of alloys and a non-metal material employed as an alternative to GRP and which Sigma calls a ‘Thermally Stable Composite’ (TSC). It’s designed to maintain those fine tolerances through a greater range of operating temperatures. That said, this lens isn’t weather-proofed so it will need to be protected in other ways when being used in extreme conditions… although, as it happens, we used it in a blizzard when the wind-chill factor was pushing temps towards -10 degrees Celsius and it continued to operate flawlessly throughout.

Sigma builds the 24mm f1.4 Art with mounts for Canon, Nikon and its own bayonet fitting, with Sony’s A mount to become available shortly (although this lens is a prime candidate for the FE mount). The mounts themselves are milled from solid lumps of brass for enhanced durability.

The all-glass optical construction comprises 15 elements in 11 groups and it’s here that Sigma weaves its magic as nine of these elements are special types in one way or another. Three are made from Sigma’s ‘“F” Low Dispersion’ glass which has been formulated to give a refractive index and dispersion characteristics similar to those of fluorite-type elements.

To this day, fluorite crystal elements are hugely expensive to make but extremely effective at minimising chromatic aberrations so a number of lens makers have worked on finding suitable alternatives. Sigma says its FLD elements have anomalous dispersion characteristics “very similar to those of fluorite” and so are able to correct for residual chromatic aberrations, working in conjunction with the 24mm’s four ‘Special Low Dispersion’ (SLD) types.

Also in the mix are two aspherical elements which correct for distortion, but by placing one of these elements at the very rear of the lens, it also provides some correction for sagittal coma flare (a smearing or streaking of point light sources that’s particularly problematic with wider angle lenses because of the more acute angle-of-incidence at which the light rays are refracted towards the edges of the frame).

The 24mm also has Sigma’s ‘Super Multi-Layer Coating’ to minimise ghosting and flare, and it has a nine-bladed diaphragm to give more rounded out-of-focus effects. Autofocusing is via Sigma’s ‘Hyper Sonic Motor’ (HSM) ultrasonic drive, but a full-time manual override is provided for any subsequent fine-tuning. The focusing group is internal so the barrel length remains unchanged and the front element – which accepts 77 mm diameter screwthread filters – doesn’t rotate. The minimum focusing distance is 25 centimetres, allowing considerable scope for shooting close-ups combined with the 24mm’s interesting perspective and the highly selective focus inherent with the very shallow depth-of-field at f1.4. In practice, this combination of focal length and maximum aperture creates a surprisingly versatile lens with the obvious applications being landscapes, city scapes, street photography, environmental subjects and even some sports where you can get close to the action.

Thanks to the degree of correction provided by its optical design, to this list can be added architecture, interiors and astrophotography.

We tested Sigma’s 24mm f1.4 Art lens on a Canon EOS 6D body and then, because it was conveniently also being tested at the time, the EOS 5Ds. In theory at least, there’s no reason why this lens shouldn’t be up to the challenge of 50 MP resolution (especially as Sigma’s ‘A1 MTF’ measuring system uses a 46 MP Foveon direct RGB image sensor).

Sharpness is obviously the key here and there’s no question this lens is exceptionally sharp, even at f1.4 although here there’s some fall-off towards the corners. This steadily improves at f2.0 and f2.8, leading to remarkable centre-to-corner uniformity from f4.0 to f11 (at f16 diffraction starts to become an issue). Likewise vignetting – a.k.a. brightness fall-off – which is quite pronounced at f1.4, but completely gone by f4.0.

Particularly commendable is the correction for distortion which succeeds in almost completely eliminating any barrel-type bending. Only when a straight edge is located immediately adjacent to a frame edge is the slightest curvature evident. Lateral chromatic aberration is also well handled to the extent that it’s unlikely to be an issue in 99 percent of situations. Flare and ghosting are both effectively suppressed even when the sun is included in the top of the frame, and while some flare can become evident when shooting at the smallest apertures it’s tightly controlled and doesn’t unduly compromise contrast or saturation.

As noted earlier, the reasonably short minimum focusing distance opens up more creative options with this lens, especially in terms of exploiting the narrow depth-of-field wide open and the beautifully clean out-of-focus effects. These allow for selective focus to be fully exploited as a creative tool, but the 24mm’s angle-of-view complimented by the high level of correction for distortion also offers plenty of artistic possibilities using framing, composition and focus.

Obviously Canon’s rival L Series EF 24mm f1.4 II USM is included on the EOS 5Ds’s dance card of recommended lenses, but what about Sigma’s 24mm Art model? Following Canon’s recommendation of testing its 50 MP D-SLR mounted on a tripod – and using its mirror lock-up-with-delayed-auto-release feature to ensure a completely even playing field in terms of eliminating any movement-related sources of possible softness – the Sigma lens performed impressively well, resolving the very fine detailing with commendable definition and crispness. Optimum sharpness is delivered between f2.0 and f8.0. The smoothness of the tonal gradations and the contrast characteristics are on a par with those of the various L Series primes we used on the EOS 5Ds. The bottom line here is, indeed, the bottom line as the Sigma 24mm Art has the advantage of being significantly more affordable, especially compared to its direct rivals from either Canon or Nikon.

The Verdict
This is a lens to fall in love with. Aside from the brilliant performance, it handles beautifully on any mid-sized or pro-level D-SLR, the proportions and weight making for a very well-balanced combination (especially on the former). It’s also very comfortable to handle and, while it would be nice if the focusing collar offered a little more rotational travel, it certainly allows for fast manual operations. The real highlights in terms of the optical performance are the high degree of correction for both distortion and chromatic aberrations, but the overall sharpness (even at full aperture), contrast and attractive out-of-focus characteristics all add up to a fast wide-angle prime that’s technically one of the best on the market. Throw in the considerable creative potential, a surprising degree of versatility and the wallet-friendly price tag, and Sigma’s 24mm f1.4 Art becomes a strong alternative to the camera makers’ own best offerings.

Sigma 24mm f1.4 DG HSM Art: $1049

Price: $1049.

Format: For full-35mm format or ‘APS-C’ size sensor D-SLRs. Focal length on the latter is equivalent to 36mm (with a magnification factor of 1.5x).

Angle-of-View: 84.1 degrees (diagonal).

Construction: 15 elements/11 groups.

Minimum Focus: 25 cm.

Maximum Reproduction Ratio: 1:5.3.

Aperture Range: f1.4 – f16.

Overall Length: 90.2 mm.

Maximum Diameter: 85.0 mm.

Filter Diameter: 77 mm.

Weight: 665 grams.

Lens Mount(s): Canon EF, Nikon F (D-type AF), Sony A and Sigma S-AF.

Features: Two aspherical elements, three ‘FLD’ (“F” Low Dispersion) glass elements, four ‘SLD’ (Super Low Dispersion) glass elements, internal focusing, nine-blade diaphragm, ultrasonic AF drive, full-time manual focus override. Lens hood and carry pouch supplied. Compatible with Sigma’s USB Dock for firmware upgrades.