The Sigma 17mm F4 DG DN Contemporary ($599) is an exceptionally slim, carry-friendly lens, which is no small feat given its extra-wide angle of view and full-frame coverage. The I Series is defined by its metal-barrel design cues and on-lens aperture control, both on full display here. And we have little bad to say about its picture quality. There are alternatives to consider depending on what camera system you use, but the 17mm F4 is a fine lens and excellent value in either E-mount or L-mount, especially for creators who prefer small, discrete primes over zooms.

The Widest I Series to Date

The 17mm F4 DG DN Contemporary is part of the Sigma I Series, a subset of lenses that share the same design concept and language. Like its brethren, this prime is housed in a black anodized aluminum barrel and includes a matching metal hood and magnetic metal lens cap. Size-wise, it's one of the slimmer entries, not far off in concept from the not-as-wide 24mm F3.5 DG DN Contemporary, and easier to carry than any of the upsized F2 entries.

It's quite an accomplishment considering the extra-wide angle of view; a lens like this is simply not possible to make for SLRs. But mirrorless systems benefit from a short distance between the lens and sensor, along with EVFs that work better with in-camera digital correction. The result is a full-frame 17mm F4 that's just 7.9 ounces, 1.9 by 2.5 inches (HD), and supports 55mm front filters.

Sigma markets the lens for L-Mount Alliance and Sony E-mount cameras; we received the E-mount version to test. Sony's system is more popular and has been around longer, but there aren't that many direct alternatives to consider. The Zeiss Batis 18/2.8 costs twice as much, while the budget-minded Rokinon 18mm F2.8 isn't a standout performer.

If you're using an L-mount system, the Panasonic Lumix S 18mm F1.8 is the nearest alternative. Sigma also has the 20mm F2 DG DN Contemporary for L and E cameras, one of the aforementioned larger entries in the I Series (2.9 by 2.8 inches, 13.1 ounces). It captures a slightly narrower view, but gathers four times as much light as an F4.

As for the angle of view, a 17mm prime isn't one most will think of as an everyday lens, though the extra-close focus available here helps you find interesting frames in scenes that don't lend themselves to a wide prime. Personally, I find this type of lens to be a good match for cityscapes and street photography that emphasizes architecture, along with interior studies and landscapes. For video, the angle is plenty wide for self-recorded vlog footage, though vloggers with full-frame cameras may prefer a bigger f-stop for the blurred-background effect.

Handling and Controls

The 17mm F4 keeps it pretty simple for controls—it includes an aperture control ring, an AF/MF toggle switch, and a manual focus ring. The aperture ring goes from f/4-22, clicks in at third-stop detents, and has an A position for automatic and on-body control. Silent, click-free operation isn't supported, however, something to consider if you're mulling the lens for cinema projects where iris pulls are commonplace. Vloggers and single-camera operators are less likely to miss it.

A stepping (STM) motor drives autofocus; it responds quickly enough, as the wide-angle optical formula doesn't require a high-speed linear actuator. Autofocus is acceptably quiet to use for video. For manual focus, the lens responds nonlinearly on Sony cameras, but can be swapped to linear response if you get it in L-mount. Photographers tend to prefer nonlinear manual focus, which allows for precise or roughshod focus racks based on how quickly you turn the focus ring, while cinema users will want a linear response for focus pulls that can be repeated across multiple takes.

The focus breathing effect is visible, but is rather modest. You'll notice a bloom in the angle of view for video shots that rack from the macro range to a more distant plane of focus, but it's not a problem for vloggers recording present-to-camera footage or similar applications where the plane of focus may shift slightly during a shot, but not dramatically.

Close focus is a strong point, and while the 17mm F4 doesn't quite make the macro grade, it does support 1:3.6 magnification at its nearest 4.8-inch focal distance. It adds some versatility, though we'll say that nature photographers may want to think twice about an I Series lens. Sigma includes a gasket around the lens mount to help keep dust and moisture outside, but it is not fully weather-sealed.

Sigma 17mm F4 Contemporary: In the Lab

I matched the Sigma 17mm F4 DG DN Contemporary with the 60MP Sony a7R IV and Imatest software to check its optical performance. The lens scores in the very good range at f/4-5.6 (4,150-4,250 lines), but delivers excellent marks from edge to edge at f/8-11 (4,600 lines).

The high-pixel sensor limits picture quality at smaller apertures, so we see softer results when using the lens at f/16-22. You may want to use f/22 to get starburst effects in landscapes, but the sunstars here aren't crisply defined despite the wide view. The tines split apart, and are only clear at f/22.

The 17mm F4 does a good job with flare control, a plus for a lens that might be used for sunrise and sunset landscapes. You can point it right toward the sun and still end up with a photo with strong contrast and details. We noticed some ghosting in the form of false green reflections in some instances, but it's avoidable with subtle changes to your angle.

False color in backgrounds, however, is not something you can sidestep so easily. The 17mm F4 shows some LoCa, or false green and purple halos, visible in defocused areas of the frame. On the other hand, lateral chromatic aberration, a purple color effect around points of high contrast that are in focus, isn't visible in typical problem areas.

The 17mm F4's optics show visible barrel distortion, but in-camera corrections compensate for it (and some dimness toward the corners) when using the lens to snap JPGs. A correction profile is embedded in Raw files for easy processing in compatible software like Capture One. Adobe Lightroom requires a custom profile; Sigma gave us an early look at the forthcoming Lightroom profile and we found that it worked properly. Straight lines are important for a lens like this that's sure to have some architectural applications.

The I Series Goes Wide

Sigma's I Series is an appealing line for photographers after classic metal barrel style at a midrange price. The tiny 17mm F4 DG DN Contemporary is the widest-angle entry to date, with a view that's comfortable for applications ranging from architecture and cityscapes to self-recorded vlog footage.

As a value option, the Sigma 17mm F4 is unmatched; you won't find others of its quality and angle for around $600. The Rokinon 18mm F2.8 for Sony may cost less, but it isn't nearly as good a performer. Meanwhile, the nearest option in L-mount is the more video-minded Lumix S 18mm F1.8, which puts more of a strain on budgets at $900.

In all, we're quite impressed with what this little lens can do. Pictures are sharp and focus is snappy, and there is something to be said about the I Series aesthetics. There are some downsides, notably some false color in backgrounds and a lack of full weather protection, but those are reasonable compromises for a mid-priced prime.