In article <4ai0om$rlr@morgoth.sfu.ca>, ssbartle@sfu.ca says...
>Hi I would like to know if there is anyone who has used the Tamron >20-40 2.7-3.5 w/ a circular polarizer or though Sigma 18-35 3.5-4.5
>with a polarizer. Is it possible , does it vignette ? (...)

Any standard-design polarizer would almost certainly vignette.
If either of the two lenses have a 72mm filter size, the Nikkor
polarizer should fit (the glass is larger than the mounting ring
to avoid vignette). If you have never used a polarizer on a super
wide lens, I would recommend borrowing one before buying - the
wide coverage insures very uneven polarization over the field
of view. BTW, I would also recommend borrowing one of the
two lenses mentioned and see if you like w/a zooms.
This w/a nut didn't (and the 20mm f2.8 Nikkor
should provide noticeably higher quality
images than either lens mentioned).
Hope this helps.