Constant f/2.8 aperture combined with dual XD Linear Motors delivers exceptionally fast, precise autofocus and sharp handheld results, supported by 5-stop Optical SteadyShot stabilization. Its optical formula, featuring one XA element and four ED elements, produces high corner-to-corner resolution with smooth, clean bokeh that avoids onion-ring artifacts. This lens is best for landscape and event photographers who need a weather-sealed, full-frame telephoto zoom with reliable performance in challenging light.