the AT-X 11-20mm f/2.8 PRO DX Lens from Tokina offers a 17.5-32mm equivalent focal length and features a constant f/2.8 maximum aperture for maintained brightness throughout the zoom range. One P-MO hybrid aspherical element and two glass-molded aspherical element work in tandem to Minimize distortions and control various aberrations while three SD ultra-low dispersion elements reduce chromatic aberrations for increased clarity.