By reducing the distance from the rear of the lens to the focal plane and reducing the size of the image circle to match the size of the APS-C imaging sensor used in digital SLRs such as the EOS 20D camera and Digital Rebel camera,Canon's EF-S lenses reduce the size, weight and cost of wide-angle lenses for these cameras while at the same time producing high image quality with superb resolution and contrast at all focal lengths.
EF-S 17-85 F4 IS USM
This new EF-S lens brings true wide-angle to telephoto coverage to EOS 20D camera and Digital Rebel camera photographers. It features Canon's Image Stabilization system, allowing safe hand-held photography at shutter speeds up to three steps slower than otherwise possible. And of course, it's optically optimized for digital SLRs. A ring-type USM delivers fast and silent auto focus, as well as full-time manual focus when in the AF mode.
The EF-S 17-85mm f/4-5.6 IS USM lens provides a 5x zoom ratio and an angle of view equivalent to a 27-136mm lens on a 35mm camera. The new lens also uses a glass-molded aspherical lens element with aspherical surfaces on both sides for superb image quality throughout the entire zoom range and it features a closest focusing distance of 12 inches at all focal lengths. The EF-S 17-85mm IS lens is 5% shorter and 12% lighter than the EF 28-135mm IS lens and accepts 67mm filters.
Construction 17 elements in 12 groups Angle of view Diagonal Angle of View: 78° 30' - 18° 25' Closest Focusing Distance 0.35m - 1.15 ft. Filter Size 67mm Dimensions (Length x Diameter) 3.6" x 3.1" / 92mm x 78.5mm Weight 16.8 oz. / 475g Notes Focus Adjustment: Inner focusing system, with focusing cam Zoom System: Ring USM