Tamron 17-35mm f/2.8-4 Di Lens - Canon A037 (5453) The 17-35mm F/2.8-4 Di OSD (Model A037) is an ultra-wide-angle zoom lens that combines superb image quality with outstanding portability and is the lightest and smallest size in its class. It uses four LD (Low Dispersion) lens elements to minimize axial chromatic aberrations. With two GM (Glass Moulded Aspherical) lenses it provides the sharpness and contrast demanded by high-end lenses and can also handle peripheral point image reproducibility. Furthermore this lens has repeatedly gone through Tamrons proprietary ghosting analysis simulation which is employed to resist backlighting problems from strong light sources to which wide-angle lenses are often subjected. Along with an enhanced high-level optical construction the lens has BBAR (Broad-Band Anti-Reflection) Coating which is highly effective in reducing reflection and controlling ghosting and flare. The front lens element is coated with a protective fluorine compound that is water and oil-repellent. This makes the lens surface easier to wipe clean and less vulnerable to the damaging effects of dirt dust moisture and fingerprints. Moisture-Resistant Construction and leak-proof seals in the lens barrel protect the lens when shooting outdoors. The Minimum Object Distance (MOD) is a close 28cm throughout the entire zoom range. You can enjoy pleasing bokeh (background blurring) when shooting at wide-open aperture with this ultra-wide-angle zoom thanks to the rounded aperture blades.