I have a Nikon D700 and a NN5 and don't know what lens to get. Earlier I used a Canon EOS 20D with NN3MKII and Sigma 10-20, and I was pretty satisfied with the result. I don't have the money to invest in a Nikkor 14-24 right now, so I'm considering Nikkor 20/2.8, Sigma 20/1.8 or Sigma 12-24. I'm not willing to invest in a fisheye at the moment, as I also want to use the lens for ordinary landscape photography. Right now the widest I've got is 28 mm, which is a bit on the long side for spherical panoramas. Any recommendations? Anyone using 20 mm on FX/fullframe? Is that wide enough? A good balance between number of shots and image quality?