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Specifications for the EF 17-40 f/4L USM The EF17-40mm f/4L USM utilizes a combination of one high-precision molded glass aspherical lens and two replica aspherical lenses to achieve the extended zoom range, while also correcting for a variety of aberrations that arise during zooming. Moreover, a Super UD (ultra-low dispersion) glass element minimizes the chromatic aberration of magnification that tends to occur with wide-angle lenses, eliminating color bleed along the edges of the subject and realizing high image contrast and resolution.
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