This L-series superstar has dust- and moisture-sealed build, and fast and quiet autofocus. The low distortion numbers at the longer focal lengths (0.12%, 0.19% pincushion) promise straight subject lines. Close-focus? An amazing 10.6 inches.
Still the lightest of the ultrawide zooms, though not lightweight in price. It boasts rugged construction, with sharpness, distortion and light falloff all above average, and a close-focusing distance of 9.4 inches. Tight!