Sigma 18-35mm f/1.8 DC HSM Art Lens

With the D7500 breaking the 20 megapixel barrier, I was slightly concerned whether my lenses would deliver sufficient acuity for the new camera.

And this is how the The Artist benefited from the The Accountant's decision to buy a refurb: The money that I saved buying a refurbished camera was applied to a used Sigma 18-35mm f1.8 DC HSM | A lens. I bought my used lens in like-new condition from a very reputable retailer (with a no-questions-asked return policy). The lens is flawless as far as I can tell. I really poured over it and couldn't a single blemish. And over the couple hundred photos I've shot with it so far, it has performed exactly as expected.

Nice Piece of Glass

I've lusted after the Sigma 18-35mm since it first came out in 2013. Sigma was the first and, as I write this, still the only maker to produce a f/1.8 constant-aperture zoom lens. But surprisingly, the 18-35 is also one of the very sharpest APS-C DSLR lenses available. It's received extremely positive reviews. I've had a very good experience with my other Sigma "Global Vision" lens, the 17-70mm f2.8-4 DC Macro (OS)* HSM | C. So I was very jazzed about this lens. More so than about the new camera, actually!

The 18-35mm focal length range is narrow, but as I discuss below, very useful.

How does it actually shoot? Well, I'm damned impressed. It's not perfect. But it is very, very good.

The Sigma focuses very fast and in very low light. In fact, the auto-focus speed is good as the Nikon lenses I own. When sticking to the central, cross-type auto-focus sensors, auto-focus is quite accurate. Unfortunately, I can't say the same for the 18-35's auto-focus performance with the off-center sensors. It simply misses focus more. It's mostly an issue at large apertures where the focus really has to be nailed. If I were doing event or sports photography where you have to work quickly and key moments are gone in an instant, I'd either be doing a lot of focus-and-recompose or I'd be stopping down the lens to give myself some depth-of-field buffer. I could probably work with it though because, frankly, I tend to figure out ways to mitigate weaknesses with my gear and I don't spend much time hand-wringing over it.

Image-wise, the sharpness, color rendition, bokeh are all outstanding in my opinion. Actually the sharpness is superb, except when the auto-focus occasionally misses as I wrote about above. Even wide-open, the sharpness is excellent. Softer towards the edges of the frame when zoomed out, but still very good. Bottom line, the image quality is fantastic.

And the build quality is first-rate with the one notable exception that it isn't weather sealed. That's a shame given that it's not an inexpensive lens. But the fit and finish is excellent. The zoom and focus rings, AF/MF switch, lens cap, and hood all have a nice, positive action to them with no extra play. (One helpful hint about the lens hood: Hold it by the ribbed section near the base and it will go on and come off much more easily!)  It has a heft that lends an aura of quality that is, candidly, just a placebo effect (weight doesn’t necessarily correlate to quality). In reality, the weight of the 18-35mm is more of a disadvantage because it is decidedly heavy for an APS-C lens. But it sure looks and feels the part!

Game Changer

Having an f/1.8 aperture available over the entire zoom range is a game changer and that's not an overstatement. Within that 18 to 35mm range, the Sigma levels the playing field with full-frame cameras.

Consider: The low light performance of full-frame is worth roughly a 1 stop advantage over APS-C for the same image quality. In other words, all other things being equal, a full-frame camera at ISO 3200 has about the same level of noise as an APS-C camera at ISO 1600. Now consider that f/2.8 is the defacto standard speed for quality full-frame zoom lenses. The Sigma is 1.3 stops faster, basically eliminating all or most of that low light advantage. To put a very fine point on it, with the Sigma 18-35mm you can use half the ISO setting because you have twice the light coming through the lens. And with the larger aperture, the Sigma will achieve comparable shallow depth-of-field to a full-frame camera with an f/2.8 zoom at the equivalent effective focal length. Moreover, the Sigma has excellent sharpness wide open. You're not forced to stop it down.

The 18-35mm lets you have your APS-C cake and eat it too. So yeah, a bona fide game changer.

Assuming It's a Half-Court Game

Don’t get me wrong. Despite what some reviewers have whined about, 18-35mm on APS-C is an extremely useful range. Think about it this way: In the full-frame world, the 28mm, 35mm, and 50mm primes are undeniable classics and there’s a very good reason for that. They cover a healthy swath of the range needed for meat and potatoes photography. The Sigma replaces all three of those lenses with a single zoom that has comparable or better performance to any APS-C primes in that range. Would more range be useful? Yes, of course. But the range provided is very valuable, nonetheless.

The bigger issue is how it fits in a set of lenses, especially Nikon DX. The Achilles heel of DX remains focal length coverage with high-end image quality. It's currently not possible to assemble a set of DX lenses – F or Z mount –  that delivers truly comparable image quality across the entire 14-200mm range that FX shooters take for granted (I’m talking about the FX lens trinity of 14-24, 24-70, and 70-200). What the DX world needs desperately is a set of f/1.8 zooms, with class-leading image quality, going all the way from about 10mm to 135mm (which is roughly the coverage of the classic f/2.8 FX lens trinity). Of corse you can just buy FX lenses, but that’s paying a premium for sensor coverage you don’t need. Sigma delivered with the 18-35mm and their excellent 50-100 f/1.8, but gaps remain unsolved. It would be great if Sigma or somebody else completed the set, but that's not going to happen for DSLR. Maybe mirrorless, but not DSLR.

Perhaps understandably, Nikon have focused their high-end innovation efforts on their full-frame products and relegated DX to "value-oriented" designs. They clearly want their customers to think of DX as merely a stepping stone to FX. And my impression from online chatter is that Nikon has largely succeeded in fostering that perception. But Fujifilm have proven that APS-C is a viable professional format. It would be wonderful if Sigma's success with truly innovative and performant APS-C lenses motivated other manufacturers to take the format as seriously. Prior to the Global Vision initiative, Sigma was perceived as a low-end, budget-focused brand. It seems to me to be a great strategy to move up-market into a niche that Nikon and Canon are reluctant to serve, for fear of cannibalizing full-frame camera sales.

Meanwhile, Back in Smallville

Anyway, in my present reality, I still have concerns about whether my ultra-wide and telephoto zooms can resolve well enough for the D7500, but at least my most-used focal lengths are well-covered. Even with the considerable overlap in focal length range, right now I think I'll be keeping the Sigma 17-70. Its extra reach and convenient size/weight is very useful for travel and walk-around scenarios.

My Nikon 35mm f/1.8G on the other hand, I'm less sure about. There's really nothing the 35 can do that the 18-35 can't do better. On the other hand, it's not like I have a lot of money bottled up in the 35mm so selling it is not going to fund much of anything. And I suppose there is one way in which the 35 is better than the 18-35. Like the 17-70, the 35 is smaller, lighter, and more discrete. I'm just not sure yet how much utility that buys me. Time will tell. [Update: I did in fact end up selling the 35mm. It was a nice, inexpensive lens made redundant by the Sigma.]