The sigma 18 35mm f18 dc hsm lens is the first wide angle zoom lens as of 22nd april 2013 to achieve a maximum aperture of f18 throughout the entire zoom range this lens incorporates a wide glass moulded aspherical lens with special low dispersion sld glass to compensate for aberrations and curvature at the widest angle has a 9 blade rounded diaphragm to create attractive round bokeh at large aperture settings and an inbuilt hsm hyper sonic motor that ensures a silent high speed a