http://www.nikonchat.com/sigma-24mm-nikon/

Nikon or Sigma Lens?
So I was looking for a new lens. It begins again. I wanted a cheap, good wide angle lens. Around 20mm, 24mm or 28mm, preferably 28mm. D50/N8008s is for a Nikon. I know these will not be huge, but wider than my 50mm and 70-300mm. I found the Nikon 28mm 2.8 really great. I've also found the Sigma 28mm 1.8. What you want to know which version of Sigma, with the opening of f1.8, be better than the Nikon? Would so sharp, richly contrasting, and big as a Nikon lens? Any other suggestions would be greatly helpful. Thank you. I was looking at a maximum price of about $ 300, maybe a little more.
I have a D50, I love the Tokina 12-24 f / 4, find specifications and reviews elsewhere. Not cheap, but very good, and 1 / 2 the Price of Nikon. Good luck.
Sigma 24mm F1.8 EX MACRO AF Lens 24mm – Microglobe.co.uk