A superwide zoom lens joins a very small club with its constant f/3.5 aperture. Can it deliver the kind of sharp images that justify the cost and extra weight?
The Sigma 10-20mm f/3.5 EX DC offers a near-fisheye 10mm, and its f/3.5 largest aperture remains constant throughout the zoom range. That’s no small task from an optical engineer’s point of view; in fact, its predecessor, the Sigma 10-20mm f/4-5.6 EX DC HSM, has a variable aperture, as do most ultrawide digital zooms. To accommodate the wider aperture and keep it constant, Sigma had to include additional glass elements that add to the lens’s weight and size, so it weighs over 18 ounces and measures a bag-busting 3.4x3.5 inches.
The Sigma 10-20mm f/3.5 is available in Canon, Nikon, Pentax, Sony, and of course, Sigma DSLRs with APS-sized sensors.
Among similar independent-manufacturer ultrawide zoom lenses, the Sigma f/3.5 is one of the biggest and heaviest—but it also is among the fastest, and the only one that zooms out to 10mm and has a consistent largest aperture (the Tokina 11-16mm ATX Pro DX has a consistent f/2.8 maximum aperture and is an ounce heavier). The Sigma 10-20mm f/3.5 costs $650, which is about $150 more than a slower, variable–aperture lens in the same zoom range.
I took the Sigma 10-20mm f/3.5 EX DC to New York City, then put it on a tripod and shot some high-resolution subjects. How did it do? Let’s find out.
Look and feel
I was impressed with the lens’s matte flecked black finish and solid feel. Zoom was smooth and consistent, but the focusing ring provided a bit too much resistance. Focal length markings are clear white on black and feet and meters are indicated in a focus window. Since this lens is designed for small-sensor DSLRs, aperture is controlled via camera controls and there is no aperture ring. There is no image stabilization, but focus can be switched from AF to manual via a switch on the side of the lens. The lens accepts 82mm filters, and the front does not rotate during focus.
On the street
One of the first things I looked for was distortion, which is typically pronounced for lenses in the near-fisheye range. At 10mm, there was indeed some pillow distortion although it is moderate. At 14mm, all distortion was gone. At 20mm, very slight pincussion distortion was visible. Edges showed very slight color fringing, but nothing objectionable, even when viewing a 12MP image at 100%. There was a small amount of light fall-off from center to corners.
When shooting in line with direct sunlight, some flare was observed, but well controlled at 10mm, thanks to its Extraordinary Low Dispersion glass elements and a Special Low Dispersion element, as well as its Super Multi-Layer coating, although at 20mm flare is pervasive when shooting even at a slight angle to the sun. Fortunately, the included petal-type lens hood took care of that, and I highly recommend using it at all times.
In general, images were sharp and contrasty, with very little optical distortion except when shooting within a few feet at 10-15mm. The f/3.5 lens allows for shallower depth of field than typical with a zoom lens of this kind, although at the minimum aperture of f/22 depth of field is practically from about 2-3 inches to infinity. The close focus gets extremely close, in the range of around three inches!
Focus was fast, quiet, and decisive in daylight although it was a bit more hesitant (by fractions of a second) in low light and low contrast.
Weighing a decision
The lens’s bulk may eliminate it from contention for some folks, who may prefer to trim the weight and size by choosing a variable-aperture lens instead. Some variable aperture lenses, such as the Pentax SMCP-DA 10-17mm f/3.5-4.5 or the Olympus Zuiko 9-18mm f/4-5.6, are as small and light as typical kit lenses. The pricing is also somewhat high for the focal range but justified because of its unique larger, fixed maximum aperture, which always adds to cost.
But if you don’t mind the bulk and can handle the extra cost, you get an outstanding, premium lens that will give you great performance and sharp photos at all focal lengths