From Manufacturer:
An advanced one-lens solution, the EF 24-105mm f/4L IS II USM is a Canon L-series zoom covering wide-angle to short-telephoto focal lengths and featuring a constant f/4 maximum aperture. The version II of this popular lens sports a redeveloped optical design, which includes four aspherical elements to significantly reduce distortion and spherical aberrations throughout the zoom range for great sharpness and accurate subject rendering. Individual elements feature an Air Sphere Coating, too, to suppress flare and ghosting for greater contrast and color accuracy in harsh lighting conditions.

Complementing the refined optics, this 24-105mm f/4 also sports a ring-type USM and internal focusing mechanism to enable quick, quiet, and accurate autofocus performance, as well as full-time manual focus override. A four-stop-effective Image Stabilizer is also used to minimize the appearance of camera shake for sharper handheld shooting. Additionally, this lens is weather-sealed and has a protective fluorine coating on the exposed elements for use in trying environmental conditions.