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 & multiple zoom groups allow internal focusing resulting in high image quality throughout the zoom range. Compatible with Extender EF 1.4x & 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 & are resistant to dust & moisture. Ultrasonic focusing A ring-type ultrasonic motor drives autofocus extremely quickly & 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 & enhance contrast. They also reduce flare & ghosting – a common problem caused by light bouncing off a camera's sensor..