Conclusion - Pros

  • Super fast constant F1.8 maximum aperture
  • Excellent optics, even wide open
  • Fast, silent autofocus
  • Solid build quality without being over-heavy
  • Compatible with Sigma's USB dock and Optimization Pro software

Conclusion - Cons

  • Restricted zoom range
  • Needs detailed AF microadjustment for best results
  • Inconsistent autofocus in difficult conditions even after microadjustment
  • Physically rather large for a standard zoom

Overall conclusion

The Sigma 18-35mm F1.8 DC HSM was announced to widespread excitement, if only for the company's sheer ambition in making such a fast zoom. But this inevitably came with a degree of scepticism - it's hard enough to make an F2.8 zoom that's really sharp wide open, so could an F1.8 zoom possibly work? Then again, Sigma's recent track record with lenses like the wonderful 35mm F1.4 DG HSM gave hope that the company might possibly be able to deliver.

What nobody quite anticipated, ourselves included, was that Sigma could conceivably deliver a lens with optics this good. The 18-35mm isn't just sharp for a fast zoom; in terms of outright image quality, it's a match for many fast primes, even when shot wide open. Obviously, the restricted zoom range will have helped, but even so this is a considerable achievement on Sigma's part. The lens can more-or-less replace a set of primes across its range with minimal compromise in image quality.

This does all come with one serious caveat though, and that's to do with focusing. We've used two copies of the Canon mount version of the lens, and found autofocus to be rather hit-and-miss with both under less-than-ideal conditions (for example with low contrast subjects). Part of the problem here is that the kind of relatively small focus errors sufficient to take the edge off the image sharpness at F1.8 are essentially invisible in the optical viewfinders of SLRs, so it's difficult to spot focus errors while you're shooting. Setting up full AF microadjustment using Sigma's USB dock and Optimization Pro software certainly helps with overall focus accuracy, but doesn't eliminate shot-to-shot inconsistency.

What this means is that while the 18-35mm has truly superb glass, autofocus problems mean that it can be difficult to get the full benefit when shooting at large apertures, which somewhat negates the lens's key selling point. Not every wide-open shot will be misfocused by any means, and you'll still get prime-like image quality when shooting stopped-down. But unfortunately, the fact that you can't rely on always getting correct focus makes the lens a bit less easy to recommend over an F2.8 zoom in the 17-50mm class.

This is unfortunate, because in almost every other respect the Sigma is an excellent lens. It handles well, with smooth zoom and focus rings and all of Sigma's latest thoughtful design touches. In terms of the less easily quantifiable aspects of image quality, it offers attractively-blurred backgrounds, and isn't overly susceptible to flare given its speed. And, of course, it's not just the fastest zoom on the market, but faster than almost any prime wider than 24mm that you can mount on an SLR (with the sole exception of Sigma's own venerable 20mm F1.8).

The Final Word

Sigma has been on something of a roll recently, with lenses like the 35mm F1.4 offering excellent optics at a very competitive price, and it's clear from both technical tests and real world shooting that the 18-35mm F1.8 is following on in much the same vein. Its relatively narrow zoom range is undeniably a little restrictive, but on the other hand, the image quality it can offer over that range is absolutely stellar. It's let down a little by inconsistent autofocus, which makes it difficult to get consistently sharp results every time when shooting wide open. But if you're prepared to live with this, the 18-35mm is capable of delivering truly exceptional results.

Sigma 18-35mm F1.8 DC HSM Art
Category: Normal Lens
Optical Quality
Build Quality
Autofocus
Ergonomics and Handling
Value
PoorExcellent
Conclusion
The Sigma 18-35mm F1.8 DC HSM is an extraordinary lens, offering prime-level image quality in the fastest zoom ever made for SLRs. Its 28-50mm equivalent range is a little limiting though, and inconsistent autofocus means that it can be difficult to make the most of the excellent optics when shooting at large apertures.
Good for
Enthusiast APS-C users looking for the very best image quality available from a normal zoom, and willing to spend a bit of time setting up autofocus micro-adjustments or using live view focusing for the sharpest results.
Not so good for
Photographers who like to travel light, or need a wide-ranging zoom.
86%
Overall score

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