10-13-2015, 08:52 AM
Oh, you're spoiled! 
Of course there are a few 20/21mm f/1.8 lenses out there but they're rather exotic anyway, and the Sigma isn't exactly a stellar performer (the performance of Nikon and the Voigtländer is still an unknown value, at least I don't remember any Voigt tests, and the Nikkor hasn't been tested here yet; Lenstip and SLRgear have tested it and it looks like it has its share of issues as well).
Of course there are a few 20/21mm f/1.8 lenses out there but they're rather exotic anyway, and the Sigma isn't exactly a stellar performer (the performance of Nikon and the Voigtländer is still an unknown value, at least I don't remember any Voigt tests, and the Nikkor hasn't been tested here yet; Lenstip and SLRgear have tested it and it looks like it has its share of issues as well).