Rest on its laurels? Not Sigma. Just look at the updated version of its bright 50-150mm f/2.8 digital-only (DC) zoom ($675, street), part of the company's top-drawer EX family of glass. Its predecessor performed admirably in the Pop Photo Lab just two years ago (January 2007). Since then, the company's engineers have twisted, squeezed, and tweaked its design in an attempt (we're guessing) to catch up to the optical superiority of Tokina's remarkable 50-135mm f/2.8. Reaching out to the full-frame equivalent of approximately 77.5- 232.5mm, the Sigma's zoom range is just slightly longer than the film-era 70-210mm moderate tele zoom standard. Its APO designation comes by way of its four elements of SLD (Special Low Dispersion) glass-more than any other DC lens. Other noteworthy attributes: A new lens design claimed to maximize image quality at the closest focusing distances, plus compatibility with Sigma teleconverters, which can extend focal length out to a 465mm equivalent. Throw in the HSM motor-delivering fast, silent, and sure autofocus-and you've got quite a lens.
While it weighs about average for its class (and a few ounces less than the Tokina), the lens measures about 1/4-inch longer than its rival. Still, it cast no shadow at any zoom setting or focusing distance when used with the built-in flash of our test camera, the Canon EOS 50D. Sigma skipped the tripod collar-we found the Tokina's useful. Focusing and zooming internally, the lens has a fixed length in use, suiting it to macro ringlights, Cokin-type filter holders, and other lens-mounted accessories. Barrel markings are adequate, except for the subject distance scales (feet and meters), a low-contrast gray-on-black that's challenging to read in low light. The HSM focusing motor performed superbly, and the lens offers one of the silkiest manual-focusing actions (and broadest MF rings) in its class. The zoom action is almost as outstanding and a noticeable improvement over the original version of the lens, which we faulted for its stiffness.