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.

• Focal Length & Max. Aperture: 17-40mm 1:4
• Filter Diameter: 77mm
• Magnification with Extension Tube EF12: 0.83x - 0.32x
• Magnification with Extension Tube EF25: 1.02x - 0.70x
• Diagonal Angle of View: 104?? - 57?? (43.2mm)
• Horizontal Angle of View: 93?? - 49?? (36mm)
• Lens construction: 12 elements in 9 groups
• Minimum aperture: f/22