Because it is a very high quality but moderately-priced ultra wide angle zoom lens, the Canon EF 17-40mm f/4.0 L USM Lens is one of Canon's best selling lenses.
 
The 17-40 f/4 L fills out the bottom focal length range of Canon's f/4 L zoom lens series. It is the lightest L lens currently made (1.1 lbs / 475g) and is the smallest L zoom lens currently produced (3.3" x 3.8" / 83.5mm x 96.8mm - DxL).
 
As indicated by the "ultra wide angle" designation, the 17-40mm focal length is ultra wide on a full-frame DSLR.

Compatible with All Canon DSLR Formats L-Series Lens - The Best Canon Makes Super Wide Angle Zoom Lens For Film or Digital SLR Cameras Uses 3 Aspherical Lens Elements Uses Super UD Glass Water and Dust Resistant Internal Zooming and Focusing Circular Aperture Diaphragm Accepts 77mm Filters

In The Box   *  Canon EF 17-40mm     F/4.0 L USM lens *  Dust cap *  Lens cap

Canon EF 17-40mm f/4.0 L USM Lens

 

General Length 4 in Diameter 3.3 in Weight 17.6 oz Lens System Lens System Wide-angle zoom lens Special Functions Zoom,  Wide angle Focal Length 17 mm - 40 mm Lens Aperture F/4.0 Optical Zoom 2.4 x Magnification 0.24 Min Focus Range 11 in Focus Adjustment Manual , Automatic Zoom Adjustment Manual Max View Angle 104 degrees Min View Angle 57.5 degrees Lens Construction 9 group(s) / 12 element(s) Filter Size 77 m Diaphragm Blades 7 Lens Coating Super Spectra coating Mounting Type Canon EF Features UD glass,  Aspherical lens,  Rear filter mount,  Rear focusing system,  Ultrasonic Motor (USM),  Internal focusing system,  Full-time manual focusing.