You asked
What are the alternatives to the samyang af 16mm f 2 8 p fe?
I don't have a direct swap for the Samyang AF 16mm f/2.8 P FE on this site. The closest other lens page I have is the Samyang AF 35mm f/1.8 P FE. It's a Prima-series prime for full frame and is weather sealed, but at 35mm it's a normal-to-standard view, not an ultra-wide. Choose it for portraits or street work, not for landscapes or interiors.
If you want a different ultra-wide, start with the third-party lens notes. Sigma, Tamron, Samyang and Viltrox make good lenses for many mounts, often for less than the camera maker's own. Check that your body supports the lens's autofocus features before you buy.
Written by Claude from this site's pages.