Ultra-wide angle lenses have always been in demand by architectural, corporate, and other top pro photographers. This new lens features completely redesigned optics including 2 high-precision Aspherical elements and two totally new UD-glass elements. The result is superior image quality: better contrast and sharpness at the outer edges, and a reduction in chromatic aberrations that can sometimes be seen with high-resolution digital SLRs. Its diagonal angle of view is an impressive 114°-anything larger would be a Fisheye lens. It has a built-in lens hood, and has been dust- and moisture- proofed. The lens uses a rear focusing system, high-speed CPU, and a powerful ring-type USM with revised electronics for faster, more responsive AF. This lens continues the proud tradition of superior clarity optics found in L-series Canon lenses..