Ultra wide lens for analogue EOS SLR cameras
The EF17-40mm f/4L USM is an ultra wide angle Canon EF zoom lens meant for professional and high amateur SLR EOS camera users.

Standard zoom lens for digital EOS SLR cameras
While it is an excellent lens when used with an analogue SLR camera, the EF17-40mm f/4L USM is especially well suited for digital SLR cameras with an imaging sensor size smaller than the 35mm format. Indeed on such digital SLR cameras these focal lengths can give an angle of view approximately equivalent to that of a 28-70mm lens used on a 35mm camera, which makes it the ideal standard zoom lens.

Superior optical performance
The EF17-40mm f/4L USM has 12 lens elements arranged in 9 groups. Super Spectra Coating on the elements ensures excellent colour balance and minimises ghosting and flare. To provide superb image quality over a 17-40mm zoom range the lens uses three aspheric elements of two different types, while Super UD (Ultra-low Dispersion) glass is used to prevent the chromatic aberrations that often can degrade the subject edge clarity.

Extensive set of high-end features

• Minimum focusing distance is just 28cm throughout the entire zoom range.
• The Auto-focus works silently and quickly thanks to a fast central processing unit with an improved AF algorithm. You can override AF mode with manual focus should you wish.
• Controlled by an electromagnetic diaphragm, the EF17-40mm f/4L USM’s circular aperture can achieve a more attractive appearance to out of focus background areas in a picture.
• The front of the lens does not rotate as you focus. This means, for example, that polarising filters still function effectively as you zoom in and out. At the rear of the lens there’s a drop-in gelatin filter holder.
• 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.

A new and affordable L-series ultra-wide-angle zoom lens that's ideal for both film and digital SLRs. Superior optics are assured by the use of three Aspherical lens elements, in addition to a Super UD (Ultra-low Dispersion) glass element. Optical coatings are optimized for use with digital cameras. This lens focuses as close as 11 inches (0.28m), and offers both Canon's full-time manual focus and a powerful ring-type USM for fast and silent AF. It has a constant f/4 maximum aperture, and offers the choice of screw-in 77mm filters or a holder in the rear of the lens for up to three gel filters. Finally, it offers weather-resistant construction similar to other high-end L-series lenses.

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