Sigma's 70-300mm f/4-5.6 APO DG Macro Lens is one of several tele zoom lenses. By incorporating the autofocusing motor into the lens itself, it can now autofocus with all Nikon DSLR cameras (including the D40, D40x, etc.). In addition, with the motor built into the lens, focusing will be quieter and more responsive.
This lens is a compact Apochromatic tele zoom lens incorporating two Special Low Dispersion glass elements in the front lens group, plus one Special Low Dispersion glass element in the rear lens group, to minimize chromatic aberration.
The DG lens design corrects for various aberrations. This lens is specially coated to get the best color balance while also cutting down on ghosting caused by reflections from the digital image sensor.