Recently I found people shaving the lens hood off their Nikkor 10.5mm Fisheye which is a DX lens to use it on a full-frame Nikon DSLR. The result is a wider field-of-view but not even completely circular, more like a wheel-barrel.
What are the advantages of this? Why not just buy a Nikon-mount Sigma 8mm Circular fisheye instead? Or just get a rectangular full-frame fisheye? Has anyone seen how panorama software angle these types of images?
The lens warranty goes void and the damaging is permanent.