Introduction Introduced in 2003 the EF 17-40 f/4L USM was one of the first of the lightweight pro-level L-series zooms from the firm adopting a constant f4 aperture. Not only does that make the lens relatively small and more portable compared with the f2.8 varients, but it also helps keep it moderately priced. This full-frame lens is also popular with users when mounted on APS-C cameras where it’s the equivalent to a 27-64mm. Like other L-series lenses from the company, the EF 17-40mm f/4L has a high grade optical construction consisting of three aspherical lens elements
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