The only lens this wide and this fast is very impressive Sigma's new 20mm f/1.8 EX DG Aspherical DF RF is the fastest lens of its focal length (or the widest lens of its speed, it you prefer to look at it that way). It's also a very good lens.
Available in mounts for Canon, Minolta, Nikon (D), Pentax and Sigma AF 35mm SLR cameras, the new superwide-angle lens autofocuses as close as 7.9 inches, providing a maximum reproduction ratio of 1:4, and—more importantly—the ability to move in very close for those mind-tweaking expanded-perspective shots.
To sort through the alphabet-soup designation (don't you wish someone would just once name a lens something simple like "really fast 20mm superwide"?), EX means the lens is part of Sigma's top-of-the-line "Excellence" pro-lens family; DG means it's especially well suited for use with digital SLRs, with a superwide angle of view to offset the "quasi-telephoto" effect of the small image sensors used in many digital SLRs and more-even light distribution at large apertures; DF means the lens utilizes Sigma's Dual Focus mechanism (slide the focusing ring forward, and it won't move during autofocusing, making for easier hand-holding); and RF means the lens incorporates rear focusing, which moves only the small rear lens group rather than the large front element, making for quicker autofocusing, and simplifying use of orientation-sensitive lens attachments such as polarizers and graduated filters, since the front element doesn't rotate during focusing. Aspherical means the lens incorporates aspherical elements (in both the front and the rear groups) to minimize the distortion, spherical aberration and astigmatism inherent in superwide-angle lenses. Other features include nine diaphragm blades for a pleasant effect in out-of-focus foregrounds and backgrounds, and the use of lead- and arsenic-free "ecological" glass.
Specs include 13 elements in 11 groups, a minimum aperture of f/22, a filter size of 82mm, a diameter of 3.5 inches, a length of 3.4 inches and a weight of 18.3 ounces—not bad for a 20mm lens that's more than a stop faster than anyone else's.
In Use
The first things to cross our minds when we heard about this superfast superwide-angle lens were edge brightness, vignetting and distortion (optical distortion, not the perspective expansion you get at very close shooting distances, which is a matter of physics, not a lens failing). Well, as you can see in the accompanying photos, exposure is even across the image frame, there's no evidence of vignetting, and distortion is almost nonexistent.
Of course, other things are important, too, like sharpness, contrast, color rendition and flare resistance. Again, our test lens did extremely well on all counts. Autofocus performance on a variety of Canon EOS camera bodies was excellent, and exposures were quite accurate.
The Sigma 20mm f/1.8 is comfortable in use (remember to slide that focusing ring forward when using AF mode), with good balance on all the camera bodies we tried it on, and it autofocused quickly and accurately on all the bodies. The focusing ring makes a swishing sound during focusing that took a little getting-used-to (it's no louder than the sound of other Sigma lenses we've used, just different), but when that's the worst you can say about a lens, it's quite a lens!
Street price is around $360, including a cutaway lens hood and a dandy padded forest-green lens case. Sigma Corp. of America, 15 Fleetwood Ct., Ronkonkoma, NY 11779; 631/585-1144; www.sigma-photo.com.
