Three glass mold aspherical lenses provide excellent correction for distortion, color aberration and field curvature. The inner focusing system corrects the fluctuation of aberration to maintain image quality regardless of the focal distance. Sigma's Super Multi-Layer Coating reduces flare and ghosting and provides sharp and high contrast images even at the maximum aperture. The superior telecentric optical design improves image quality throughout the frame. This lens benefits from a newly developed linear AF motor which moves the lens elements directly without the need for gears or the drive of other mechanical parts. This system ensures accurate and quiet autofocusing, making the lens suitable for video recording as well as still photos. The lens features a rounded 7 blade diaphragm creating an attractive blur to the out of focus areas of the image. This Sigma 19mm F2.8 EX DN has a minimum focusing distance of 20cm/7.9in and a maximum magnification ratio of 1:7.4.