This f2.8 lens sets a new standard for all zooms. Its unusually large maximum aperture is made possible by an extra-wide aspherical lens to provide higher optical performance in a number of ways . including effective anti-flare features and crisp-to-the-edge images. An internal focusing mechanism allows the front of the lens to remain stationary and to easily accommodate specialty filters, such as polarizing filters. Sigma's original 4-group zoom mechanism keeps size and weight to a minimum while fully correcting astigmatism and distortion. Its wide range and convenience make it perfect for snapshots and great travel photos.