EF 17-40mm f/4L USM
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.

Benefits
- Superb optical performance throughout the zoom range
- Fast autofocus speed
- Highly resistant to dust and moisture
- 28cm minimum focusing distance at all focal lengths

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.