Some may ask how this lens compares to the Nikkor 16mm f/2.8. Despite the difference in focal lengths, the two lenses appear to have the same angle of view. The Nikkor is slightly larger, and its built-in hood isn't as good. The 16mm doesn't focus as close and appears to still be the same optical design as the original introduced in 1979! The Nikkor is more expensive, but I don't think it delivers better results. (Admittedly, I no longer have a 16mm to directly compare against the Sigma 15mm, but my memory of the 16mm makes me believe that the results I've gotten from the Sigma are slightly better.) Frankly, I don't know of anything that would make me want the Nikkor over the Sigma, especially considering the price differential.