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Ultra wide angle zoom lens with professional qualityEF 17-40mm f/4.0L USM – a new high quality ultra-wide angle zoom lens. This new model offers a wider zoom range, with both wider and longer focal lengths, as well as a constant maximum aperture of F4 and autofocusing speed at least equal to that of the class leading EF 16-35mm f/2.8L USM lens.
While the 2.4x, 17-40mm, zoom range provides excellent versatility and creativity for the film camera user this set of focal lengths will also be particularly useful to digital SLR users. When used with an APS-C sized imaging sensor, as is used in the new Canon EOS 10D and the existing EOS D60, these focal lengths give an angle of view in a similar range to that of a 28-70mm lens when used on a standard 135 format camera.
This new lens will be welcomed equally by film and digital camera users. Its focal length range and the unique Canon technologies used in its design and construction will provide photographers with an indispensable high quality, well corrected, optical tool.
Minimum flare, maximum focus
To ensure distortion-free images the EF 17-40mm f/4.0L USM uses three aspheric elements of two different types, while Super UD glass is used to prevent the chromatic aberrations that often degrade subject edge clarity. Additionally, lens coatings have been employed to inhibit ghosting and flare caused by internally reflected non-image forming light. By increasing the power of the group of elements controlling focus Canon has brought the close focus point of the lens to just 0.28m at all focal lengths.
Canon's EMD (electromagnetic diaphragm) gives a more attractive appearance to out of focus picture areas by means of a circular wide aperture diaphragm that produces smoother tonal transitions. A second diaphragm in this unit is used to further reduce the risk of flare and to improve overall contrast in captured images.
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