TechRadar Verdict

While Sigma’s lighter, much cheaper and slightly wider 35mm f/1.4 DG HSM | Art lens is perhaps a more sensible option for many, the 40mm f/1.4 DG HSM | Art lens's sterling optical performance deserves high praise.

Pros

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Excellent sharpness, even wide open
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Great corner sharpness at f/1.4
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Lovely out-of-focus areas
+
Solid build quality
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Virtually non-existent chromatic aberration

Cons

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Noticeable vignetting at widest apertures
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AF sounds picked up on video
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Very large for a 40mm lens
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Far pricier than other logical alternatives
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Heavy

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Sigma has spent the last few years redefining what DSLR and mirrorless users should expect from third-party lenses, with many of its Art-series optics in particular released to laudatory reviews. Now, with many popular options ticked off, the company has stretched out to deliver a handful of more unusual options.

The optic on test fits in this category as much as it doesn’t. Canon, Nikon and Pentax all offer 40mm lenses, for example, and this focal length is slightly closer to the “standard” 43mm for 35mm-based system than the more common 50mm. Yet, its particularly wide aperture makes it unique, and it’s not often we see such a lens breach four figures in both price and weight. Furthermore, unlike the options from the above manufacturers, it’s neither a macro lens nor a pancake lens, but has a more conventional (if large) design.

Features

Hyper Sonic Motor with manual override
9 blades promise a rounded diaphragm
3 FLD and 3 SLD elements

The lens is one of the latest of Sigma’s prime lens to have a f/1.4 maximum aperture, having been announced at the same time as the Sigma 56mm f/1.4 DC DN Contemporary and 28mm f/1.4 DG HSM | Art Optics. As a ‘DG’ lens it’s most at home on a full-frame body, although it will also work with cropped-sensor cameras, whereupon its effective focal length is around 55mm, depending on the specific camera used.

If you’re thinking 40mm is an odd choice for stills photography, it probably won’t surprise you to learn that inspiration behind the lens appears to be the company’s CINE line of optics. The company has stated that this is the “first lens developed originally to live up to the sought-after angle of view and performance standard for a benchmark cine lens.” To that end, it reassures users that it delivers the kind of resolution that befits 8K recording.

Inside its barrel, 16 elements are arranged over 12 groups, with three of these being “F” Low Dispersion (FLD) and a further three being Special Low Dispersion (SLD). This means we should expect chromatic aberration to be minimal, while the further aspherical element positioned at the back of the optical array should help to combat further distortions. Specifically, Sigma promises 1% distortion and non-existent coma, the latter being a bugbear of many wide-aperture optics.

Sigma also promises beautiful bokeh from the optic, which is no doubt partly down to the use of nine aperture blades that promises a rounded diaphragm. Multi coatings have also been applied to the elements to keep flare and ghosting low, and a petal-shaped lens hood with an integrated lock is also supplied as standard to shield the lens from extraneous light.

Specifications

Focal length: 40mm

Mount: Canon EF, Nikon FX, Sigma, Sony E

Filter size: 82mm

Max aperture: f/1.4

Maximum magnification: 0.15x

Dimensions: 87.8 x 131mm

Weight: 1,020g

If you’re lucky enough to use one of Canon’s most recent DSLRs, you’ll also be able to take advantage of the Lens Aberration Correction feature on these bodies to iron out any minor aberrations that may remain. Nikon users, meanwhile, who can apply their own corrections applied manually on their camera, have the advantage of electromagnetic diaphragm control, which allows for smooth autoexposure changes when shooting continuously.

The HSM suffix indicates the use of a Hyper Sonic Motor, and autofocus can be overridden by manual control through the focusing ring. A 0.15x magnification rating means you won’t be calling upon it for macro work, but its minimum focusing distance of 40cm means you can still get reasonably close to your subjects.

As with Sigma’s other recent lenses, the optic is also compatible with the USB dock for the purpose of firmware updates and performance optimisation.

Build quality and handling

Dust- and splash-proof design
Solid barrel
Focus ring has a wide angle of rotation

The lens is about as long as the 85mm f/1.4 DG HSM Art, which itself is considered to be fairly large for an 85mm f/1.4 lens, but slightly less bulbous and with a filter thread that’s 4mm smaller. It should be fairly obvious from its size and heft, if not from its generous f/1.4 maximum aperture, that this is a lens designed for more considered use – and Sigma appears to have crafted it with build to match.

Various seals protect the lens against dust or any splashes of water, with a rubber ring around the back to form a more secure connection when mounted, and this is complemented by a coating on both the front and rear element to help repel oil and water. The mount feels sturdy and the rubber ring the encircles it only comes out a little, but it doesn't appear to need to be any further out than it is. The rear element is very close to the back of the lens, however, so care should be taken when removing and replacing the lens.

The lens adheres to the same minimal design as other Art-series primes, with a smooth finish on the barrel and a deep focusing ring towards the front. A small window displays focusing distance in both feet and metres, which is useful, although, particularly on such a large lens, some may have preferred this window to be a little larger and it’s markings a little more prominent. But these are small points.

The only switch on the barrel flicks between manual and autofocus, and this gives easily and clicks positively between the two positions. The focusing ring has a pleasingly large angle of rotation too, which makes critical adjustment of focus convenient.

Performance

Good autofocusing performance
Excellent sharpness, even wide open
Noticeable vignetting at wide apertures

Focusing speeds are generally good, particularly when there’s plenty of light. ‘Fast’ is perhaps stretching it – the weight of the elements is no doubt partly why this is the case but it will be fast enough for most subjects. You can hear the focusing system work in the absence of any ambient noise too, which is something to bear in mind if you want to use this during video, but this is masked by ambient noise outdoors.

Sharpness is already excellent in the centre of the frame at f/1.4, and corners hold up remarkably well at this point, but as soon as you stop down consistency across the frame is excellent. Chromatic aberration is also remarkably absent from images. There’s the faintest touch of lateral chromatic aberration in some scenes, but traverse aberrations are superbly controlled, which is very reassuring when you consider just how frequently this lens will be relied upon at its widest apertures.

Image 1 of 10

Canon EOS 6D Mark II with Sigma 40mm f/1.4 DG HSM Art, 1/320 sec at f/1.4, ISO100

Click here to see the full-size image

Moderate vignetting can be seen at f/1.4, to the point where it appears that the image is underexposed as a whole, but this improves significantly at f/1.8. It continues to lessen until you get to around f/2.8, after which point it’s not an issue in real-real-world images. Perhaps better correction should be expected from such a design, although no doubt rectifying this optically would necessitate an even larger and heavier construction. It’s also likely that your camera will be able to lift away the worst of this though its own corrections. On the Canon EOS 6D Mark II we used the correction was significant, although a touch of vignetting remained.

Depth of field at f/1.4 is very shallow and out of focus areas have a very pleasingly smooth character. While the level of vignetting is no doubt why some cat’s eyes-shaped bokeh can be seen in the peripheries of the frame, in the centre of the frame it’s perfectly round at f/1.4.

Verdict

With a lofty price tag and the performance of other Art-series optics setting a high standard, we should expect a lot here – and we certainly get it.

The lens is capable of resolving superb detail and beautifully round bokeh, with excellent control over chromatic aberrations and virtually absent curvilinear distortion. It’s also solidly built and, given that its closest rivals are either manual focus only or slower in terms of maximum aperture, right now it appears to without any direct competitions from other brands.

Indeed, if anything rubs off the lens’s shine, it’s Sigma’s own alternatives. With the company’s also-excellent, much lighter 35mm f/1.4 DG HSM | Art retailing at almost half the price, that lens appears as a far more practical solution for anyone wishing to use it handheld. The 50mm f/1.4 DG HSM | Art is also very well regarded, and likewise significantly cheaper, although its angle of view is noticeably narrower. Of course, these are not the same optics, although the fact that you can pick up both for only a little more than the 40mm f/1.4 DG HSM Art alone is something to think about.

To sum up, the Sigma 40mm f/1.4 DG HSM Art may be large and heavy, and potentially as impractical as it will be affordable for most, but its optical performance is hard to fault. The only significant downside that you're likely to come up against in everyday shooting is pronounced vignetting at wider apertures, although this is often used creatively, of course, and can be easily rectified where necessary.