The ef 16 35mm f28l iii usm is a premium quality ultra wide angle zoom lens with a constant f28 maximum aperture for the highest image quality possible even in low light conditions versatile collection of wide angle focal lengths ef 16 35mm f28l iii usm features a 16 35mm zoom that incorporates a range of wide angle focal lengths premium image quality large diameter double surface glass moulded gmo lenses and ultra low dispersion help to significantly improve image distortion and reduce chroma