The Sigma 35mm F1.2 DG DN Art ($1,499) is another big, heavy lens, a continuing design trend in the industry. It backs up its heft with impeccable optics, excellent build quality, and a relatively attractive asking price. If you're willing to deal with its size, it will deliver impeccable shots with an extremely shallow depth of field. But you shouldn't discount good f/1.8 or f/2.8 alternatives, like Sigma's own 45mm F2.8 DG DN Contemporary, which delivers strong optical performance in its own right, in a much smaller, more affordable package.

Heavy Optics Required for F1.2 Aperture

The Sigma 35mm F1.2 comes in at 5.4 by 3.5 inches (HD) and 2.4 pounds. It's massive for a prime, especially when you consider that you'll be pairing it with a mirrorless camera rather than an SLR. Its front element is big too, requiring 82mm filters. A hood, caps, and carrying case are included.

The large size is necessitated by the aperture. At f/1.2 it captures about 50 percent more light than an f/1.4 lens. In order to do so, and deliver images that are sharp from edge to edge, larger, heavier glass elements are a necessity. For comparison, Sony's FE 35mm F1.4 ZA is about a pound lighter and an inch shorter.

It's an example of a recent trend. Sigma also makes a big 40mm F1.4 for SLRs, and we've seen first-party mirrorless options swell in size too. Canon's RF 50mm F1.2 L is another example. Sigma doesn't sell the lens for Canon cameras, however. You can get it for Sony E-mount bodies, as well as L-mount cameras made by Leica, Panasonic, and Sigma.

There are alternatives available. Sony offers the small FE 35mm F1.8 for E-mount, and L-mount owners can look to the svelte Sigma 45mm F2.8. Of course, you'll sacrifice light gathering to get there—the f/1.8 lens is nearly a full stop slower than the f/1.2, and the f/2.8 option is two stops behind.

Built Tough

The 35mm F1.2 is housed in a sturdy housing, a mix of metal and polycarbonate materials. It's protected against dust and splashes, like many of the cameras with which it will be paired, and also incorporates fluorine protection on the front element. It prevents smudges or water droplets from adhering to the surface, especially helpful given its large size.

Controls include a manual focus ring, finished in textured rubber, and an aperture control ring with a knurled metal finish. The aperture ring can be set from f/1.2 through f/16 in third-stop increments and also has an A position to move aperture control to the camera body. The ring can also be set to turn smoothly, without detent clicks, a plus for video work where smooth iris adjustment is desired.

It's easy enough to switch between the two options—a switch on the barrel toggles aperture clicks. Other on-lens controls include an AF-L button and the standard MF/AF focus toggle. Some cameras will allow you to adjust the AF-L button's function—on our a7R IV test body, I was able to set it to perform dozens of sundry functions.

Autofocus is quick, but not entirely silent. I noticed a slight clicking noise when using the lens in AF-C. It's not overly loud—you won't hear it over background noise—but it can appear on video soundtracks if you're using your camera's internal microphone. There have been some reports of focus inaccuracy when pairing the L-mount version of the lens with Panasonic cameras, but I wasn't able to try the combination myself. In my short time with the L version of the lens and a pre-production Leica SL2 I enjoyed accurate autofocus.

Focus is available to 11.8 inches, measured from the sensor. This gives the lens a good close-up working distance, so you'll rarely have to back away from a subject to get a shot. It's good enough to net 1:5.1 life-size reproduction at the closest focus distance.

There's no optical stabilization, which isn't surprising. The feature isn't commonly found in bright prime lenses. But, with more and more cameras offering in-body image stabilization (IBIS), and the bright aperture making shorter shutter speeds possible in many situations, it's not a big concern.

Incredible Resolution

I paired the 35mm F1.2 with the 60MP Sony a7R IV and the 47MP Leica SL2 in the field, and tested it in the lab with the a7R IV and Imatest software. Its imaging capabilities are, in a word, fantastic. At f/1.2, it manages 4,414 lines on a center-weighted evaluation, but there's no drop in quality as you move from center all the way to the edges of the frame. You'll get resolution that is excellent, wide open, from edge to edge.

There's a slight improvement at f/1.4 (4,542 lines) and f/2 (4,696 lines). At f/2.8 resolution crosses into outstanding territory (5,385 lines), which is maintained all the way through f/8. We see a modest drop at f/11 (4,558 lines) and a bigger one at f/16 (3,918 lines), but really, you should feel comfortable using any f-stop. You'll be able to capture shots with multi-point sunstars at f/16.

See How We Test Digital Cameras

Optics aren't absolutely perfect. The lens shows modest barrel distortion, about 2.2 percent, which may detract from scenes with perfectly straight lines. You can correct for this pretty easily—if you use Adobe Lightroom you'll enjoy one-click correction, but most Raw processors offer manual distortion correction.

There's also a vignette visible at f/1.2 and f/1.4. The Lightroom profile removes it, brightening corners so they're as well illuminated as the center of your image. It's not something you'll notice in every shot, and you may prefer to leave it unadjusted, as it gives portraits a natural frame.

Cost of Performance

If all we cared about was resolution, the Sigma 35mm F1.2 DG DN Art would be a five-star performer. You will be hard-pressed to find another lens to match it. It opens to f/1.2, something that few full-frame lenses offer, and delivers outstanding resolution from center to edge. Add in build quality that's decidedly pro, and you've got a lens that can capture stunning scenes, and do so in environments where you daren't take others.

You pay for this, though not in the way you might expect. At $1,500, the Sigma 35mm is certainly pricey, but it's not out of line. The Sony FE 35mm F1.4 costs $100 more, and while Panasonic doesn't sell a 35mm in L-mount at this point, its Lumix S Pro 50mm F1.4 costs $2,300.

But, if you're walking around a city with your camera around your neck, or on your feet from day to night covering a wedding ceremony and reception, the Sigma 35mm F1.2 DG DN weighs on you. Whether or not you're willing to live with that is your decision entirely.

I'm happy that lenses like the Sigma 35mm F1.2 DG DN Art exist. They've got a lot of appeal for photographers who value performance over everything. But, aside from the f-stop, you won't lose much by opting for the $750 Sony FE 35mm F1.8, a 9.9-ounce featherweight, or Sigma's own compact 45mm F2.8 DG DN Contemporary.

Best Lens Picks

• The Best Fujifilm Lenses for 2020
• The Best Leica M Lenses for 2020
• The Best Micro Four Thirds Lenses for 2020
• The Best Pentax SLR Lenses for 2020
• More Lens Reviews
• More from Sigma

Further Reading

• Tamron Details Affordable 70-180mm F2.8 Zoom Lens
• The Best Sony Mirrorless Lenses for 2020
• The Best Nikon Lenses for 2020
• The Best Canon Lenses for 2020
• Oops! $13K Camera Lens Sells for $95 Due to Prime Day Error