I have owned one Sigma lens in my life, the ultra-wide, full-frame 12-24mm f/4.5-5.6. That was several years ago, and I didn’t much care for it. It wasn’t horrible, by any means, but I was shooting an APS-C camera at the time and the lens I really wanted was the Tokina 11-16 f/2.8 (which is still one of the best wide-angle lenses available, in my opinion). Jump forward a few years and things have changed over at Sigma. Their Art-series primes have consistently blown photographers away on full frame cameras, and it seems every new lens they churn out just gets better. So when Sigma announced the APS-C specific 18-35mm f/1.8 about a year ago, crop frame shooters had a very good reason to get excited.
I know I am late to the game with this review, but for whatever reason, I did not get a chance to shoot this lens until recently and believe it is well worth talking about again for anyone who may have missed the initial buzz. While most camera and lens companies will try to sell you, say, an f/2.8 lens for an APS-C camera and pretend it offers the same light-gathering ability as it would on a full frame, Sigma wasn’t afraid to admit the truth: it’s not the same at all. In fact, an APS-C sensor has slightly less than half the surface area of a full frame sensor, leading to the well-known term, “crop factor.” Crop factor is used to determine equivalent fields of view, but what’s less commonly known is that field of view isn’t the only thing different on smaller sensors. Light sensitivity and depth of field are also affected by the crop factor, so f/2.8 on APS-C is equivalent to f/4.2 on full frame. Therefore, Sigma’s 18-35mm f/1.8 is roughly equivalent to a full frame 28-50mm f/2.8.
Of course, the lens we all want it to be equivalent to is the 24-70mm f/2.8, a common multi-purpose lens popular among both Canon and Nikon professional shooters. I’m sure Sigma could have made a 16-46mm f/1.8 to achieve both equivalent aperture and focal length, but this would have resulted in an even bulkier lens, unwieldy on most APS-C bodies—and that’s to say nothing of what would have happened with the price. Instead, Sigma chose to focus its attention on a more limited zoom range, thus ensuring the lens would be sharp, fast, and affordable. And I have to say, they delivered.
The first thing I noticed was the heft of the lens; it is quite large given the limited range, and it’s very dense. The weight is welcome, though, as everything feels very well-made, from the metal bayonet mount to the smooth focus and zoom rings. I shot this lens on a Nikon D7100, which features a 24MP sensor that foregoes the traditional low-pass filter for added sharpness. If ever there were a camera to put this lens to the test, it would be this one. The lens actually has a good balance on the D7100 and is by no means difficult to hand hold, but I imagine on smaller bodies it would feel (and look) a little awkward.
Anyone familiar with Sigma lenses will be well-aware of autofocus issues. To my luck, I found the test copy of this lens to focus correctly, but it is compatible with Sigma’s USB lens dock for making advanced focus micro-adjustments should you need to. Compared to many Nikkor lenses, the AF performance is a little slow, but not slow enough to warrant complaining. It uses a silent ultrasonic motor similar to Nikon SWM or Canon USM systems, so while it may not beat first-party AF speed, it’s no slouch, either.
Of course, what we all really want to know is how the lens performed optically. I found the semi-wide to normal focal length range to be perfect in a party atmosphere for candid photos of guests. One of my main worries was if an f/1.8 zoom lens could actually be sharp wide open, but those worries have been completely put aside. This lens is brilliant wide open. It was clearly designed to be shot at f/1.8, and is optimized to such an extent for wide apertures that it actually suffers somewhat at smaller apertures (more on that later). I would have no problem recommending this lens to event shooters with APS-C cameras, but lacking telephoto range means you may also want to carry around a separate portrait lens like a 50 or 85mm. For the most part, I also found it to render pleasing background and foreground blur for portraits, but I did notice some instances where the bokeh became a little muddy, specifically with busy backgrounds.
As a landscape lens, the Sigma was a bit of mixed bag. It renders scenes with great overall contrast and color across the entire aperture range, but I was a little miffed by a smudging of detail in micro-contrast areas: small blades of grass, branches, woodgrain, etc. There was also noticeable chromatic aberration at small apertures (f/8, f/11) that was actually worse than it was wide open. Chromatic aberration was all but gone at the telephoto end of the zoom, but at 18mm it was very apparent. Now, in Sigma’s defense, some of these issues could have been operator error on my part from failing to control the depth of field correctly. The lack of micro details could also be the “fault” of the camera: with 24 million pixels, the D7100 has a very small pixel pitch, making it extra-sensitive to chromatic aberration and causing diffraction to kick-in around f/4 or f/5.6. So, shooting at f/8 to f/16 means less detail at 100% magnification. It’s a tricky game to balance desired depth of field with desired sharpness at the point of focus. All of this said, I was very happy with my landscape photos when viewed at “normal” sizes (not 100%), but if you’re thinking about making large landscape prints, this isn’t the lens for you. But, then again, Sigma didn’t intend it to be.
As much as I expected the D7100 to challenge the 18-35mm f/1.8, I also found that the two are a great match—at least for wide-aperture work. The past few years have seen incredible advancements in imaging technology, and with crop frame sensors and lenses as good as these, going full frame is hardly necessary for all but the most demanding photographers. For the camera’s part, I was consistently impressed by the dynamic range and color depth of the D7100, which are right up there with Nikon’s full frame D800. For crop frame cameras, the Sigma 18-35mm f/1.8 may just be the best zoom lens on the market for photographers who need maximum low-light capabilities without sacrificing sharpness. Sure, I found things that weren’t perfect, but for $800 at the time of writing, I really can’t complain. This is a well-made, high-performance lens that offers APS-C shooters the same exposure and depth of field control as an f/2.8 zoom on a full frame camera, and it does it for a fraction of the price. I won’t go as far as to call it a must-buy—the short zoom range and optimization for wide apertures make it somewhat of a specialty lens not suited to every situation—but I do think that especially for enthusiasts and pros shooting a Nikon D7100 or Canon 70D, you owe it to yourself to consider this lens.
(Note: the images in this article were originally shot in raw and have been enhanced.)