Optics  16 elements in 12 groups.    Three of these elements are aspherical: one is an expensive custom-ground aspherical element, another is a replica (plastic) aspherical element and one is a glass-mounded (GMo) element.    Diaphragm  7 blades.  Stops down to f/22.  It's round until f/4 and heptagonal from f/8.    Close Focus  0.92' ( 0.28m) from the image plane    Focal Length  16-35mm.    Used on a 1.3x camera it gives angles of view similar to what a 20-44mm lens would give on a 35mm film camera.    Weight  22.375 oz. (634.3 g), measured.    The original 16-35mm weighs 1.230 oz (34.9 g) less, and the Canon 17-40mm f/4 Lweighs 5.670 oz (160.7g) less.