Balancing 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.