Bright aperture and stunning wide optics in a weather-protected package
Images, and the devices that capture them, are my focus. I've covered cameras at PCMag for the past 10 years, which has given me a front row seat for the DSLR to mirrorless transition, the smartphone camera revolution, and the mainstream adoption of drones for aerial imaging. You can find me on Instagram @jamespfisher.
The Sigma 20mm F1.4 DG DN Art's wide angle of view, well-corrected optical formula, and down-to-earth price makes it an ideal lens for creators, particularly astrophotograhpers.
After several I Series Contemporary releases in a row, Sigma is once again turning its attention to its premium Art lens series with the 20mm F1.4 DG DN Art ($899) for L-Mount Alliance and Sony E-Mount mirrorless camera systems. The lens is bulkier than compact alternatives like the Sigma 20mm F2 DG DN Contemporary ($699), but the F1.4 optical formula is highly desirable for creators, such as astrophotographers, who often work in low-light environments. It's also fully protected against the elements and features plenty of physical on-barrel controls. If you need an ultra-bright, broad-angle prime, the Sigma 20mm Art is simply a fantastic option that outperforms even the Sony FE 20mm F1.8 G at wide apertures, earning our Editors' Choice award.
Sigma splits its lenses into three lines: Art, Contemporary, and Sports. Art lenses, including the 20mm F1.4 DG DN, feature bright apertures and all-weather construction, while Contemporary lenses emphasize portability and affordability. Both lineups include wide primes. You won't find any wide-angle lenses in Sigma's Sports lineup, which is reserved for long telephotos with speedy focus motors.
The 20mm DG DN F1.4 Art is a hefty lens at about 4.5 by 3.5 inches (HD) and 1.4 pounds. It sports a big front element that takes 82mm threaded filters, though you can also use rear filters. It's not huge by SLR standards—the Sigma 20mm DG HSM F1.4 Art for SLR cameras measures 5.1 by 3.6 inches, weighs 2.1 pounds, and requires an adapter to use with mirrorless cameras, for comparison.
We're not surprised that the older lens for SLRs is bigger, as it's much more complicated to make a bright, wide-angle lens when a mirror box eats up real estate between the sensor and the lens mount. Mirrorless cameras, on the other hand, generally allow optical engineers to design smaller lenses because the rear lens elements can sit mere millimeters away from the sensor plane. In practice, that leads to more compact options with the same angle of view and still-bright apertures, such as the Sony FE 20mm F1.8 G (3.3 by 2.9 inches, 13.2 ounces) and Sigma 20mm F2 DG DN Contemporary (2.9 by 2.8 inches, 13.1 ounces).
Despite those design improvements, the Sigma lens is still quite large because it covers a full-frame sensor, opens to F1.4, and is sharp from edge to edge. All of that requires some heavy glass inside the barrel. Sigma uses lightweight materials like polycarbonate and aluminum in its construction, but you can't overcome the laws of physics. We don't expect that most photographers really need an F1.4 lens at this angle of view. But if you like to find beauty in the darkest corners; make images of the night sky; or chase soft, defocused backgrounds, this is an ideal option.
Sony's competing FE 20mm F1.8 G also features weather protection, and matches well with the company's weather-protected full-frame camera bodies. The Sigma 20mm F2 DG DN Contemporary isn't made for rainy skies, as it only includes sealing at the lens mount. The 20mm F1.4's weather protection is a differentiating factor for L-Mount system owners, as it is the only fully sealed bright prime available—neither Leica nor Panasonic currently offer a 20mm or 21mm L-Mount prime.
The 20mm F1.4 Art offers lots of on-barrel controls, which we appreciate. Most prominent is the manual focus ring, which wraps around the lens body and sports standard rubberized ridges that help with grip.
I tested the Sony E version of the lens along with an a7R IV. With that combination, manual focus is nonlinear. That means you get more aggressive focus shifts when you turn the ring quickly, and more deliberate, precise adjustments when you turn it more slowly.
Photographers tend to prefer nonlinear focus for its versatility, but videographers might find it frustrating to not be able to set focus marks for repeatable focus racks. The story is different for L-mount system owners because those cameras allow you to select a linear or nonlinear focus response in the menu. For video, we prefer the Sony FE 20mm F1.8 G for its linear focus response and lighter weight, the latter of which makes it a better option for gimbals and Airpeak drones, in particular.
The focus breathing effect is quite visible, which is another concern for videographers. The angle of view shifts along with focus and, in this case, the lens shows a broader view when you focus close. You can use the lens for most types of video without worry, but it's not the best fit for rack focus shots that shift attention between subjects.
An STM stepping motor drives autofocus. Focus is quiet, a plus for video, and speedy enough. In testing, the lens takes 0.3-second to move from its closest focus distance to infinity on the a7R IV. If you're way out of focus to start, you may notice the lag, but the lens keeps up for most situations. Bringing a slightly defocused frame into sharp view and exposing an image takes about 0.15-second. An on-barrel AF/MF toggle lets you swap focus modes on the fly.
In addition to the focus ring, the lens includes an aperture ring to set the f-stop. It is adjustable from f/1.4 down through f/16 in third-stop increments and you can enable a silent, click-free operation via a toggle switch. A second toggle lets you lock the aperture controls to the lens or select the A position. When you switch the toggle to the A position, you must use the camera body controls to set the f-stop.
Sigma includes an on-barrel function button that acts as an AF-ON control by default. On most cameras, you can customize the button's function, however. Meanwhile, a Lock toggle turns that button off and disables the manual focus ring. It's handy for night sky work when you want to lock focus in and keep it set on the stars.
Nobody should mistake this 20mm for a macro lens, but it does focus very close (about 9.1 inches from the sensor or just a few inches from the front element). It produces decent 1:6.1 life-size results and can create some dramatic photos with sweeping backgrounds. If you like the idea of a wide prime for macro work, don't forget the very affordable Tamron 20mm F2.8 1:2 Macro—it's very sharp and affordable, though it doesn't focus very quickly. Remember that the Sony FE 20mm F1.8 G manages 1:4.5 magnification, too.
I paired the 20mm F1.4 DG DN Art with the 60MP Sony a7R IV to test its resolution in the lab. Imatest(Opens in a new window) software evaluates our SFRplus test chart and shows the lens to be a nearly flawless performer. We see results close to the 5,000-line mark we consider outstanding for the a7R IV's sensor, even at the f/1.4 aperture.
Wide-open, the 20mm F1.4 shows 4,900 lines through most of the frame, with edges that still show very good contrast (4,200 lines). This is a difference-maker for photographers shooting night sky images—you can expect clear results without stopping down the lens. Astrophotography is one discipline where edge-to-edge results at the widest aperture are a practical desire.
I'm not much of an astrophotographer and my home in the Philly burbs has too much light pollution to get Milky Way shots that pop. Even so, my starry night photos show pinpoints and corroborate Sigma's promise of an optical formula that suppresses sagittal coma(Opens in a new window) . Other astro-specific features include the on-barrel Lock that keeps focus set in place even if you bump the focus ring, as well as a flared barrel design that prevents lens heating wraps(Opens in a new window) (something astro pros use to prevent condensation and fogging) from getting into the frame.
I was happy with my astro shots from a technical perspective, but if you're a dedicated astrophotographer, I recommend reading reviews from specialists to ensure the 20mm F1.4 is up to your standards. The 20mm is not Sigma's only astro lens; if you prefer a slightly tighter angle, the 24mm F1.4 DG DN Art is also marketed for astro work, but didn't do as good a job suppressing sagittal coma in our tests. Sony also sells the FE 14mm F1.4 GM, which nets an even wider view and effectively suppresses coma, but costs much more at $1,599.
With more typical f/1.4 use cases, the edges will blur. Landscape photographers tend to work at narrower settings, for instance, and, at f/5.6 through f/8, results are outstanding from center to edge. With the high-pixel a7R IV, diffraction cuts into detail at f/11 through f/16, though you may still want to use those settings to get the sunstar effect. An 11-blade aperture makes for 22-point starbursts, an uncommon look. The sunstars I got from the lens show slightly mushy lines though—we recommend the Sony FE 20mm F1.8 G's sunstars for landscape photographers who chase the effect.
Wide lenses aren't typically strong for bokeh, but it's not too difficult to achieve the blurred background look with this lens, as long as there's a reasonable amount of distance between the subject and backdrop. We're quite happy with the look of the blur too; defocused highlights are round, have soft edges, and don't look busy.
In-camera corrections compensate for some optical compromises, notably some visible barrel distortion. If you use your camera in JPG mode, you don't have to worry about this issue but we expect many people who use this lens (and especially astrophotographers) will end up working with a Raw processing tool. Sigma provided us with a Raw correction profile to use with the lens in Adobe Lightroom—it effectively removes distortion and compensates for a vignette cast at f/1.4.
Chromatic aberrations are not a big problem here. I couldn't spot any lateral CA in test shots—this effect shows up as purple fringing around dark objects against bright skies and is easy to spot around telephone wires and tree branches when present in a photo.
Longitudinal chromatic aberration (LoCa), a different effect, tends to show in the form of false purple and green color in the slightly blurred focus transition areas. The 20mm F1.4 suppresses this effect well, though it is not completely absent. I had to punch in to 200% magnification when reviewing images to spot the effect, which shows up in the detail of the Master Lock logo on the padlock in the image above. It's unlikely to be a major concern in most real-world scenarios, however.
We typically think of a full-frame 20mm lens as a specialty item. The angle is a bit too vast to use as an everyday prime, with most people opting for either a 24mm or 28mm lens instead. But wide lenses are better for landscapes and architecture work, as well as (and especially in the case of the 20mm F1.4 DG DN Art) astrophotography. The latter discipline screams for vast vistas and bright optics.
We weren't able to stress test the lens for astro work, but found it capable for the night sky shots we were able to get. As a more general performer, though, the Sigma 20mm F1.4 DG DN Art stands a step above competitors like the Sony FE 20mm F1.8 G with sharper, brighter optics; strong on-barrel controls; and an all-weather build. The Sony FE 20mm wins out on carry weight (it's about half a pound lighter), which makes it a better fit for hikers and vlog-style video on a gimbal.
Tamron's 20mm F2.8 1:2M is an affordable alternative for E-mount photographers for $250. But it's not nearly as competent in dim light and videographers won't like its loud autofocus operations. Don't sleep on it if you're on a tight budget and don't need an F1.4 aperture, though.
If you use an L-mount camera, your decision is much simpler. The only other autofocusing 20mm option is Sigma's 20mm F2 DG DN Contemporary ($699) lens. The 20mm Contemporary is part of the metal-barrel I Series line and has a few marks in its favor, including price and portability, but its F2 optics gather half the light as an F1.4 and it isn't as protected against the elements.
For either system, the Sigma 20mm F1.4 DG DN Art is an easy pick for our Editors' Choice award. You can't argue with its price, optical quality, or focus performance, and the weather protection makes it a strong fit for outdoor work. You might prefer a lighter lens like the aforementioned Sony 20mm F1.8 or Sigma F2 Contemporary, but neither opens to F1.4, which could be a deciding factor depending on your needs.
The Sigma 20mm F1.4 DG DN Art's wide angle of view, well-corrected optical formula, and down-to-earth price makes it an ideal lens for creators, particularly astrophotograhpers.
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Images, and the devices that capture them, are my focus. I've covered cameras at PCMag for the past 10 years, which has given me a front row seat for the DSLR to mirrorless transition, the smartphone camera revolution, and the mainstream adoption of drones for aerial imaging. You can find me on Instagram @jamespfisher.
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