The Canon EF 17-40mm f4 is a lightweight ultra wide angle zoom lens.

The Canon 17-40mm is especially well suited for use with digital Canon EOS SLR cameras with a focal length conversion factor higher than 1. It is the lightest L lens currently made and is the smallest L zoom lens currently produced.
{Key Features} - Superb optical performance throughout the zoom range.
- Fastest AF speed within its class (same as the EF16-35 f/2.8)
- Highly dust and moisture resistant
- 28cm minimum focusing distance at all focal lengths

{Overview}

Utilizing Ring USM, the Canon EF 17-40mm f/4.0 L USM Lens focuses very fast, quietly and accurately.

Wide landscape photography is a very popular use for this lens Use wide angles to emphasize an object in the foreground against an attractive (and mostly in-focus) background. Architecture and real estate photography often have large subjects that require wide angle lenses.

Canon 17-40 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.

Canon 17-40mm f4 Close focusing
Minimum focusing distance is just 28cm throughout the entire zoom range.

EF 17-40mm 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.

Canon 17 40 usm 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.

Canon 17-40mm f 4 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.

Canon 17-40 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. {Box Contents} - Lens Hood
- Soft Lens pouch
- Front and rear Lens caps
- User manual