The 17-40mm f/4L USM, like all of the Canon "L" lenses, delivers optical performance equal to similar fixed focal length lenses, with silent, high-speed focusing. Distortions and aberrations are remarkably small for a lens of such focal range.
The 17-40's minimum focusing distance is just 11" (28cm) throughout its entire range of focal lengths, which makes it very useful for close-up work. All of the focusing and zooming action is done internally, with no changes of the size of the lens.