 "Canon EF wide-angle lens - 20 mm" " Canon mm 2509A003 Camera & Camcorder Lenses CDW.com
"This ultra-wide-angle lens is ideal for serious applications. It is easy to hold and carry at 14.3 oz. (405g). It features floating rear focusing system. Sharp images are obtained at all subject distances." 
 "Canon EF 17-40mm f/4 L USM Lens"@en "Camera Lenses :: Canon Lens - Onestop Digital"@en
"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 f4 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.  "@en 