A zoom as good as a prime lens One of the finest telephoto zoom lenses in the EF line optically comparable to a prime lens. Four UD-glass elements to correct chromatic aberrations and multiple zoom groups allow internal focusing resulting in high image quality throughout the zoom range. Compatible with Extender EF 1.4x and 2x. Fast constant maximum aperture Shooting in low-light conditions is possible thanks to the lens\' fast maximum aperture of f/2.8 which stays constant throughout the zoom range. Such an aperture also gives control over depth of field. L (Luxury)-series quality The L-series is Canon\'s flagship professional lens range representing the best in precision-designed EF optics. L-series lenses combine superior performance with superlative handling and are resistant to dust and moisture. Ultrasonic focusing A ring-type ultrasonic motor drives autofocus extremely quickly and in near silence. Excellent holding torque ensures the point of focus is reached accurately without overshooting. Furthermore full-time manual override is available making it possible to adjust focus without leaving AF mode. Super Spectra coating Super Spectra coatings ensure accurate colour balance and enhance contrast. They also reduce flare and ghosting – a common problem caused by light bouncing off a camera\'s sensor..