Zoom lenses are very convenient. The equivalent of two or more fixed focal length lenses in one unit. The maximum aperture of some zoom lenses changes as you alter the focal length, but through-the-lens (TTL) metering takes this into account to give correct exposure.
To meet user demands for a fast EF-S zoom lens, Canon has specially designed a lens with a large aperture of f/2.8 for select Canon Digital SLR cameras. The large circular aperture produces a shallow depth-of-field, creating background blur that draws attention to the photographic subject.
The lens construction includes UD and aspherical elements, which deliver impressive image quality throughout the entire zoom range. Image Stabilizer lens groups shift to compensate for camera movement so that the image appears steady on the image plane, ensuring clear, crisp images, even in dim light.
With a Ring-type USM, inner focusing and innovative AF algorithms, this lens achieves autofocus quickly and quietly, and with full-time mechanical manual focusing, manually adjusting the focus is possible even in AF mode.