I've been looking for an extreme wide angle lens for either my Nikon F100 and F80 or for my old Maxxum 600Si. The Sigma covers the full frame, but I've read some mixed reports on the quality control of the optics. Does anyone here own and use this lens? Could you kindly give me some advice as to whether or not this lens is worthwhile? I plan to use it for B+W street shooting...sort of from the hip...very fast... on crowded NYC streets. I presently have the Nikkor 20mm f/2.8AF-D, but I want something much wider.