The ef 17 40 mm f4l usm is an ultra wide angle zoom lens that offers excellent image quality and a constant maximum aperture its compact lightweight body makes it an ideal travelling companion features superb optical performance throughout the zoom range fast autofocus speed highly resistant to dust and moisture 28 cm minimum focusing distance at all focal lengths a high quality wide angle zoom for a variety of subjects ultra wide or standard zoom the ef 17 40 mm f4l usm acts as an ul