The EF 17-40mm f/4L 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. A Super Spectra coating has also been applied to suppress flare and ghosting for improved contrast in difficult lighting conditions. Complementing the imaging capabilities, this wide-angle zoom also features a ring-type USM and internal focusing mechanism to afford quick, quiet, and accurate autofocus performance, as well as full-time manual focus override.
Ultra-wide or standard zoom The EF 17-40mm f/4L USM acts as an ultra-wide angle zoom on film or full-frame digital EOS cameras. On DSLRs equipped with APS-C sized sensors it acts as a standard zoom, giving an angle of view equivalent to a 28-70mm lens on a full-frame camera.
Close focusing Minimum focusing distance is just 28cm throughout the entire zoom range.
Superior optical performance The EF17-40mm f/4L USM has 12 lens elements arranged in nine groups. Super Spectra coating ensures excellent colour balance and minimises ghosting and flare. To provide superb image quality over the complete 17-40mm zoom range the lens uses three aspheric elements. Super UD (Ultra-low Dispersion) glass prevents chromatic aberrations.
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.
Non-rotating front element The front of the lens does not rotate, which makes using specialised filters, such as polarisers and graduates, easier. A drop-in gelatine-filter holder can be found at the back of the lens.
Smooth background blur A virtually circular aperture diaphragm gives out of focus regions a softer, more uniform feel. Sharp foreground objects stand out against a smooth blurred background.
Weather resistant Highly resistant to moisture and dust, the EF17-40mm f/4L USM is ideally suited for use in harsh environments. Environment friendly lead-free glass is used throughout its construction.
Superb optical performance throughout the zoom range
Fast autofocus speed
Highly resistant to dust and moisture
28cm minimum focusing distance at all focal lengths