This lens transforms a large-aperture F2.8 300mm lens into a zoom lens that allows you to determine the picture composition you want without having to change your vantage point. It has two SLD (the special low dispersion) glass elements in front group and another element of SLD is being used for rear group for excellent correction of chromatic aberration. New coating reduces Ghost and Flare The new multi layer lens coating and lens design reduce flare and ghost, which is a common problem with digital cameras and also creates an optimum color balance through the entire zoom range. Hyper sonic motor The AF drive for Sigma SA, Canon and Nikon cameras is equipped with a silent, responsive and high speed HSM , which also provides full-time manual focus function. Inner Focusing and Inner Zooming Since focusing and zooming do not change its overall length, this lens is easy to hold and use. In addition, since the front of the lens does not rotate, a circular polarizing filter can be easily attached and use. Sigma Apo Tele Converters (optional) High-speed focusing is possible when this lens is used with dedicated APO EX tele-converters (1.4x and 2x). By adding an APO tele-converter, which is sold separately, you can use this lens as a 168-420mm F4 AF tele-zoom lens with a 1.4x tele-converter, or as a 240-600mm F5.6 AF ultra-telephoto zoom lens with a 2x tele-converter. It is also possible to use AE (Automatic Exposure) function, even EX Tele-converters are attached to the lens.