I'm currently looking at the Sigma 10-20mm f/3.5 lens for my Canon EOS 80D (APS-C). However, one potential problem I see is that my ND-filter set is for 67mm while the Sigma lens has a diameter of 82mm. Of course I can use a step-down ring, but I'm worried that such a large difference in diameter will lead to heavy vignetting. On the other hand, the Sigma DC lenses work for all crop sensors including Nikon's variant at 1,5 CF, whereas my camera has 1,6 CF, so I'm hoping that the image circle of the lens will be slightly larger than the sensor anyway, reducing the vignetting I will get.
How bad will the vignetting be (for ND and other filters)? If you have any example images where this or a comparable combination of equipment was used, that would be great as well!