Optics  15 elements in 12 groups.  Multicoated.    Focal Length  100mm.  On the 30D, 20D, Digital Rebels, D30, D60 and 10D (1.6x factor, APS-c) it gives a field of view similar to what a 160mm lens does on a 35mm camera.    Diaphragm  9 blades.  Round to f/5.6, nonagonal from f/8 on.  Stops down to f/32.    Close Focus Ratio  1 foot (0.3 m) from the image plane. 1:1    Weight  21.980 oz. (623.2g), measured.  Ensemble with caps and hood: 24.935 oz. (706.9g), measured.  Canon specifies 22 oz. (625g).