Standard wide-angle to
telephoto zoom lens is designed for use with full-frame Canon EF-mount DSLRs,
however can also be used with APS-C models where it will provide a 38.4-168mm
equivalent focal length range. Constant f/4 maximum aperture
maintains consistent illumination throughout the zoom range. Four glass-molded aspherical
elements, including one large-diameter double-sided glass-molded lens, help to
minimize distortions and spherical aberrations throughout the zoom range in
order to maintain edge-to-edge sharpness and illumination. An Air Sphere Coating has been
applied to individual elements to reduce backlit flaring and ghosting for
greater contrast and color fidelity in strong lighting conditions. An Optical Image Stabilizer
helps to minimize the appearance of camera shake by up to four shutter speed
stops to better enable working in low-light conditions and with slower shutter
speeds. A ring-type Ultrasonic Motor
(USM), along with an internal focusing design, optimized focusing algorithms,
and a high-speed CPU, is employed to deliver fast, precise, and quiet autofocus
performance as well as full-time manual focus override. Rounded ten-blade diaphragm
contributes to a pleasing out of focus quality that benefits the use of shallow
depth of field and selective focus techniques. As a member of the esteemed
L-series, this lens has a weather-resistant design that protects against dust
and moisture to enable its use in inclement conditions. Additionally, fluorine
coatings have also been applied to the front and rear lens elements for further
protection against fingerprints and smudging.