You asked
7artisans 18mm f 5 6 vs sigma 17mm f 4 dg contemporary?
Both are ultra-wide primes for full-frame cameras, but they suit different shooters.
The Sigma 17mm f/4 DG Contemporary is the one I'd pick for most people. It has autofocus, a slightly wider 17mm view, and a brighter f/4 aperture. It mounts on Sony E and L-Mount only.
The 7Artisans 18mm f/5.6 is manual focus only, and it's slower at f/5.6. It also mounts on Nikon Z, so it's worth a look if you shoot Nikon and don't mind focusing by hand.
If you shoot APS-C, both lenses frame wider than they look on the box, so check the focal length converter before you buy.
Written by Claude from this site's pages.