Sigma 50mm f/1.4 DG HSM Art Lens Review
Bigger and more expensive than the competition, Sigma's nifty fifty is simply phenomenal.
When evaluating any lens, we focus on four key areas: sharpness, distortion, chromatic aberration, and bokeh. A perfect lens would render the finest details accurately, wouldn’t distort straight lines or produce ugly fringing around high-contrast subjects, and would create smooth out-of-focus areas.
In our lab tests, the Sigma 50mm f/1.4 DG HSM Art essentially pitched a perfect game. It's sharp at nearly every aperture across the entire frame and, when mounted on the 36.3-megapixel Nikon D810 or the 50.6-megapixel Canon EOS 5DS, it out-resolved every other lens we've tested to date. It also virtually free of visible chromatic aberration and produces very little distortion. While it's a touch soft in the corners at f/1.4, that's just about the only negative we can come up with.
A lens's sharpness is its ability to render the finest details in photographs. In testing a lens, we consider sharpness across the entire frame, from the center of your images out to the extreme corners, using an average that gives extra weight to center performance. We quantify sharpness using line widths per picture height (LW/PH) at a contrast of MTF50.
The Sigma 50mm f/1.4 DG HSM Art performed extraordinarily well in our lab tests. We actually tested it three times: once on the Canon 5D Mark III, once on the Nikon D810, and once on a beta version of the Canon EOS 5DS. The 5D Mark III results are sensor-limited, but interestingly enough the 50-megapixel 5DS and the 36-megapixel D810 are both very similar.
On the 5DS, the lens achieved higher center resolution, but produced softer corners—a difference that's likely down to sample variation. We'll discuss the D810 results specifically below (since they're a bit higher on the whole) but you can expect nearly identical results on either camera.
On the D810, the Sigma produces excellent sharpness straight from f/1.4, resolving roughly 2,200 lines in the center and a little over 1,400 lines in the corners. It improves dramatically from there, and by f/2.8 the lens is hitting 3,200 lines in the center and 2,300 lines in the corners. It peaks at f/5.6, with a center performance of 3,250 lines and the corners averaging nearly 2,900 lines. It's similarly strong at f/8, but it falls back down to around 2,600 lines by f/16.
While the 5DS results are generally similar, it's worth noting that on lower-resolution sensors—like the one found in the Canon 5D Mark III—you're not getting the most out of the lens. On that camera, the peak resolution was just about 2,500 lines in the center and 2,100 in the corners. That's still excellent, but not quite as impressive as what you'd get from the highest-res sensors on the market.
We penalize lenses for distortion when they bend or warp images, causing normally straight lines to curve.
There are two primary types of distortion: When the center of the frame seems to bulge outward toward you, that’s barrel distortion. It's typically a result of the challenges inherent in designing wide-angle lenses. When the center of the image looks like it's being sucked in, that’s pincushion distortion. Pincushion is more common in telephoto lenses. A third, less common variety (mustache distortion) produces wavy lines.
The Sigma 50mm f/1.4 keeps distortion to a bare minimum, though that's to be expected from a 50mm prime lens. In our test shots, we detected just 0.25% pincushion distortion on the Nikon D810. It's worth noting that we saw slightly higher distortion with our Canon-mount copy, but it was still under 1%—nothing to be concerned about.
Chromatic aberration refers to the various types of “fringing” that can appear around high contrast subjects in photos—like leaves set against a bright sky. The fringing is usually either green, blue, or magenta and while it’s relatively easy to remove the offensive color with software, it can also degrade image sharpness.
On all three of our test bodies, the Sigma 50mm f/1.4 produced minimal chromatic aberration. Even at f/1.4 it's not an issue, only cropping up in high-contrast scenes and only toward the extreme edges of the frame. You can find it if you go hunting, but in everyday use it'll be essentially nonexistent. What little fringing there is can be easily corrected in post.
Bokeh refers to the quality of the out of focus areas in a photo. It's important for a lens to render your subject with sharp details, but it's just as important that the background not distract from the focus of your shot.
While some lenses have bokeh that's prized for its unique characteristics, most simply aim to produce extremely smooth backgrounds. In particular, photographers prize lenses that can produce bokeh with circular highlights that are free of aspherical distortion (or “coma”).
The bokeh from the Sigma 50mm f/1.4 is, for the most part, absolutely lovely. There are a few minor issues, including some "onion ring" effect and busy-looking backgrounds under specific circumstances, but for the most part you're going to get extremely creamy-smooth backgrounds with beautifully rounded specular highlights. It's hard to ask for more from a fast fifty.
In the first sample above you can see how well the lens isolates subjects at f/1.4. Though the background isn't quite as smooth as it could be, it does a good job controlling a very high-contrast scene. In the second sample you can see how well the 9-bladed diaphragm maintains its circular shape even when stopping down to f/2. The only hitch there is the top-middle section, which looks a bit busier than we would like to see.
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