I know Sigma has the not all that sharp 12-24 FF lens, but otherwise any other great FF lenses are no wider than 14mm. I would love to see a decent quality 12mm FX lens, I don't think it can done wider without moving into the fisheye Lens territory
Now with the new Sigma APS-C lens with app 12mm effective angle, maybe Sigma should redo their old FF 12-24 lens
Anyway should Nikon make a 12mm Lens to complement their 14-24 FX lens
Pete