Hi Guys,
I am looking at the Tokina 12-24 zoom as a viable alternative to the Nikkor 12-24 unit...Does anyone have any experience with this lens and any advice as to recommended dome port size?
I was also after any general opinions as to the quality of Tokina lenses on the whole:
Quality,
Size,
Chromatic aberration,
Barrel distortion etc.,
Suitability for U/W use,
Recommended diopters, etc., etc.,
I have very little time available to me for testing and even less chance of seeing one of these lenses before purchase, so I am relying heavily on the advice/opinions of my fellow u/w 'piccie' takers...
Thanks for taking the time,
Bruce... 
I use the Tokina with my D200, have not used the Nikon, so no direct comparison, but am happy with sharpness and lack of distortion. I understan that from reading reviews, it isn't quite as good as the Nikon, but very close and the extra $400-$500 for the Nikon can be better spent elsewhere.
I use a +2 diopter behind my big S&S dome port with a 40mm ext ring.
S&S does not make a zoom gear for it, but I have found that the S&S 18-70mm zoom gear works great with if you remove the o-ring from the gear and wrap the zoom ring on the lens with a layer or 2 of electrcal tape for grip.
I am very happy with this lens, it compliments the Tokina 10-17 fisheye very well, biving me that extra reach when I want it and is an awesome topside wide angle lens. Overall, it is one of my favorites.
Hope this helps,
John