http://www.nikonchat.com/nikon-24mm-f2/

What matters most? speed or lens focal length?
im thinking of buying an ultra wide lens for my Nikon D50. im deciding between the Tokina 11-16mm f2.8 in or Tokina 12-24mm f4. ken rockwell site says that the 11-16 is better optically than the 12-24mm, but I'm not basing my decision on that (although I could update a 10MP sharpness so that helps). 1911-1916 is also $ 170 more. i like night time photography and im wondering if the extra stop is worth sacrificing half zoom range and $ 150?
If you are doing this kind of photography (on a tripod) then http://www.flickr.com/photos/little_pooky/2292613810/ bothered me that is more acute respond more quickly. But since f 2.8 is better according to what you mentioned, which would buy me.
Test — 35mm M2 Adapter