In article <427t6v$g0o@webe.hooked.net>, halbi@webe.hooked.netø says...
>I'm in the market for a "super wide" angle lens, anywhere from 17 to >20mm for
my Nikon camera set-up. I've been considering a used AF >Nikkor 20mm for around
$320, or a new AF Sigma 18mm for about the same >price, or maybe for my *small*
budget a new MF Vivitar 19mm for $120, >or used MF Tokina 17mm for $150.
Anybody out there have experience >with any of these lenses?

If you have the $320, this is an easy one: buy the Nikkor 20mm.
Not only is it about the best superwide you can buy, but if you
don't like it, you can almost certainly sell it for what you paid.
(Try doing that with any of the other choices.) IM(NS)HO, 3rd rate
glass isn't worth the money unless you just plain can't afford
good glass. BTW, if you are tempted by the shorter off-brand
focal-lengths, try comparing them with the Nikkor 20mm for
coverage - I think you will find only very minor differences
in angle-of-view (which is why I sold my 18mm Nikkor). When
you get down into 15mm territory, that's different!
Hope this helps.