The one new lens that does the work of five 18mm, 20mm, 24mm, 28mm and 35mm. A dual function, high resolution floating group lens system incorporates an aspheric lens element. This eliminates the distortion common to ultra wides and improves close focus performance. Sigma's internal focus/zoom system keeps the lens at a constant size, even while zooming, for more comfortable handling. The front end of the lens doesn't rotate, improving stability and the use of filters and hoods. Ultra compact and extremely lightweight (less than 9.8 oz.), a non-vignetting "perfect hood" eliminates flare. The exclusive ZEN finish prevents reflections and resists scratches.