You asked
7artisans af 40mm f 2 5 vs nikon z 40mm f 2?
The Nikon Z 40mm f/2 is my pick if you shoot Nikon Z. It's small, sensibly priced and simply good, and f/2 lets in a little more light than the 7Artisans' f/2.5. Both are 40mm prime lenses for full frame, both autofocus, and neither has stabilisation.
The difference is mounts. The Nikon Z 40mm f/2 is made for Nikon Z only. The 7Artisans AF 40mm f/2.5 also fits Sony E and L-Mount bodies, so it's the one to consider if you shoot Sony or Leica L. For more on what the f-number means in practice, see the aperture notes.
Written by Claude from this site's pages.