If you don't know Sigma's Art series lenses yet, you're missing out. Their well established 24mm, 35mm, 50mm, and zoom options in the Art lineup shine, but it's hard to believe it took this long for a wide-angle 20mm f/1.4 Art to make it out into the real world. But the moment I began shooting with this beauty is the moment of the past didn't matter anymore. We're in a new world: there's a 20mm to die for; and this is it.
We've been very, very patient. Sigma had zero competition, so it's no real surprise that it took this long. Nikon's still-somewhat-new 20mm f/1.8G is a great alternative for Nikon shooters that does feature Nikon's excellent Nano Coating, but it's not as good as the 24mm f/1.8G (which is obviously not as wide) that just got a rave review from DxOMark. Both lenses do fall over half a stop short of Sigma's sharp as hell, massively awesome 20mm f/1.4 Art. Thinking of Canon's EF 20mm f/2.8 USM? It may be cheap, but it's a full two stops tighter than the Sigma. And besides, it's so ugly. Just look at it...need I say more? Either way, it's the Nikon 24mm f/1.8G that we'll be considering as the only realistic alternative for Sigma's newest prime lens if image quality is a top concern.
If you're looking for the short version of this review, here it is: Just buy it -- especially if you're a Canon shooter. Then sell whatever you had before that was somewhat like it. On the other hand, if you're a Nikon shooter and don't absolutely need the f/1.4 aperture (most will find it hard to justify why you need that small difference), then you still have a decision to make. The Nikon is amazingly slightly cheaper, and beats the Sigma on sharpness and a number of other factors, even if just by a bit in both cases, and even if it's just DxOMark that currently says so. Nikon surprised us very pleasantly with their 24mm f/1.8G after their 24-70mm f/2.8E blunder. They may have a long-term chance against Sigma after all, as these are the kinds of results we've been waiting for. But back to this review of the Sigma...
This lens is packaged the same way as all of the other Sigma Art lenses: simply, but with everything you need (the lens and a case). Taking the lens out is when the real magic sets in. It's not small. Compared to the rest of the Sigma Art lineup, the 20mm is closer in size to the 50mm than it is to the 35mm and 24mm. This is in part due to its built-in hood that helps protect its bulbous front element, which brings us to our first and only real point of contention.
Because of its bulbous front element, the Sigma 20mm f/1.4 Art can't accept traditional screw-on filters. Much like Nikon's 14-24mm f/2.8 and Tamron's new-ish 15-30mm f/2.8 VC, you'll need a special, square filter kit like those made by Lee Filters in order to effect any change with polarizing filters, etc. At the same time, it's this feature that allows Sigma to deliver such a superb image. If I were a landscape photographer, I would have invested in an appropriate filter kit long ago anyway...
If there's one reason to pay twice as much for more or less the same lens in the 24mm Canon L or Nikon f/1.4G version, it's autofocus (aside from the world of difference between 20mm and 24mm, of course). The Sigma Art lenses do extremely well, but the home-cooked variants tend to perform just slightly faster in my experience. Yes, it's almost imperceptible. But yes, "almost."
Thanks to the wide angle of the 20mm focal length, however, this difference is minimized and perhaps even negated altogether. Because wide-angle lenses have such relatively large depths of field, they don't have to "adjust" as much to get to a particular point of focus. This short throw means that focus is usually lightning-fast on wide-angles. Add to that the fact that this is a prime lens, and you've got focus speeds that won't leave your wanting more.
Either way, if you want proof of how good the Sigma is overall, it's time for our first sample image:
That right there is a JPEG saved straight from the raw .NEF file without any changes.
In any case, if you never thought you'd say, "Bokehlicious," about a 20mm lens, think again. This has enough bokeh to smooth out the Eiffel Tower into an inflatable Air Dancer in the background of your street mime portrait series. In fact, I'm going to go order a second cappuccino right now... For anyone paying close attention: by "bokeh," I of course more accurately mean, "shallow depth of field."
With Nikon's f/1.8G (the 20mm and the 24mm), you still get a decent shallowness to the depth of field, or so I would imagine. I admittedly haven't had the chance to shoot with either yet, but physics is physics. And the cheaper price of either might still win your brain over, especially since we're probably talking about a relatively small perceivable difference in image quality between both of these lenses anyway. Then again, I'm sure you could still tell the difference in light transmission if you really need that extra (almost) stop. But those are all decisions you need to make.
I'm not a scientist. I'm not testing this in any special way. But when I take a look at these files taken with my relatively modest Nikon D750, I'm amazed. I've included plenty of samples (plain and not so plain) for you to mull over and form your own opinions. But contrast is punchy, color rendition is fantastic, and there's an air of sharpness surrounding every image in a way that makes me ooh and ahh over the results, regardless of whether or not I like the actual photograph in question.
You can't have a lens this wide without some noticeable distortion. And in the corners, it certainly is there. But if you're smart about shooting your wide-angle shots the way you should be by keeping recognizable objects or corners of clearly rectangular objects out of the corners, you'd be hard pressed to find any distortion that is too distracting.
That said, sharpness in the corners -- even on the edges as a whole -- degrades quite a bit due to just how wide this lens is. Honestly, it's a little more degraded around the edges than I would have expected. On the other hand, it's been a long time since I've shot anything decently wide at all. Although I may be out of touch with the "norm" for a wide-angle lens, everyone else seems to think it performs quite well. So for now, I'll chalk it up to an issue with this copy or perhaps simply an issue with my own perception of what is and is not normal.
You can take all of the "scientific" tests with a grain of salt, but it doesn't hurt that DxOMark and LensRentals like this lens, too. The new Sigma 20mm f/1.4 Art is sharper than the Nikon and Canon 24mm f/1.4 lenses in the center, and at least equal in corner resolution. That should set any last doubts at ease. Those interested in edge sharpness can enjoy the simple street shots below as examples.
I already mentioned the short version of this review above: buy this lens. But at the end of the day, we're lucky that one of our only options in the category is a fantastic one at that. The bulbous element should only disappoint the select few who constantly add and remove screw-on filters. And while there is no mention of an oil-, dirt-, and water-shedding fluorine coating like that on the front element of the Tamron 15-30mm VC (and Nikon's and Canon's super-telephotos), that's not a deal-breaker...it simply would have been a nice touch given how large the front element is. And it's not like these lenses are anything alike (though I still wouldn't blame your for having a tough time choosing between the two).
If you're a Nikon shooter, the 24mm f/1.8G offers just what this lens does and then some at a slightly more narrow field of view, except for the picky shooter's desire to get all the way to f/1.4. While I haven't shot with it yet, I would recommend trying it if it's an option for you -- you can even screw filters onto the front of that one.
As far as my needs go, consider them met. I'll be keeping this lens one way or another. Anyone want my 24mm f/1.4 Art?
(Correction: This article originally made references to Nikon's 20mm and 24mm f/1.8G lenses in incorrect orders. These errors have now been fixed.)