Wide zoom lens with minimum distortions providing filter options?

Hi,

I have the Sigma 12-24 and can confirm that it vignettes(more like pin-holes) with the cap on at the wide end. Otherwise, it is amazingly distortion free.

I'd suggest that the first question you need to answer is DX or FX. If you want a low distortion ultra-wide, you're going to have to spend some money, so best to know if you want to stay with DX or is there full frame in your future. Certainly, one of the reasons that so many folks like FX is because of the wide angle options.

A techno link: http://www.photozone.de/nikon--nikkor-aps-c-lens-tests

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Cheers,
Cedric