Editors' note, July 16, 2015: Updated with price and availability information.
Sigma's 18-35mm f1.8 excellent lens was a gift for folks with APS-C dSLRs; now the company is trying to replicate that feat with a the 24-35mm F2 DG HSM Art lens for full-frame photographers. The company's A series of lenses historically deliver great value for a reasonable price, and while it will cost a not-insubstantial $1,000 when it ships at the end of July, that's not bad for a zoom lens with that wide an aperture.
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The 24-35mm covers three staple focal lengths: 24mm, 28mm and 35mm. Sigma says its goal with the lens was to deliver prime-lens performance at those focal lengths in a single zoom.
But one of the great things about fast full-frame lenses is that they confer benefits on APS-C cameras as well. This lens will deliver the equivalent of approximately a 38-56mm lens on a Canon or 36-53mm on a Nikon, two of the mounts that will be available initially (Sigma's own mount is the third). I tend to find 24mm too wide for my needs. On the other hand, 35mm and 50mm hit my sweet spot.
The lens uses internal focus (it doesn't extend while focusing), which should make it quiet during video, and like most premium lenses uses an ultrasonic motor (Sigma's version is branded HSM, or Hyper Sonic Motor), which tend to be quieter and faster than the alternatives.
Like all of its A lenses, it has a nine-blade aperture (for round highlights) and a metal build. It's kind of heavy at a little over two pounds, but pretty compact: 4.8 inches (12.2cm) long with a diameter of 3.4 inches (8.6 cm). It can focus as close as 11 inches (27.9 cm), which isn't quite as close as its Sigma's 24mm f1.4, but about the same as the rest of its lenses in this focal range.
I'm sad it doesn't have optical image stabilization, though. I know OIS would make it bigger and heavier, but I've become addicted to the extra latitude in shutter speed that image stabilization provides. Nevertheless, I suspect I'm going to want to reserve a spot in my bag for this baby.