I love my current 18-70mm lens (see sig) but want something faster without giving up any of the focal range. All I can find is 28-70 and 17-50, etc. I use both 18mm and 70mm quite often and would hate to have to constantly swap lenses to cover such a short range. I've searched through nikon and sigma but can't find anything. Does anyone know of a quality lens on a nikon mount that will cover at least this range at a fixed 2.8 maximum aperture?