Here is a sample for you on the D500 at 13mm f/4.5 (open in new tab for larger version), which is what I typically used for optimal sharpness. I have not particularly been bothered by coma on this lens. (The 14-30mm S on a Z8 has even tighter stars, but very slightly elongated in the far corners.) Over the years I used the 12-24 f/4 a lot for nighttime and aurora exposures, although usually not tracked. Generally distortions can be an issue when tracking very wide lenses. Of course tracking on stars vs blurring of the ground is another issue to keep in mind. The seldom occasions I have done the milky way on the DX sensors, I usually have used the 10.5mm fisheye. Are you planning to use it on a dedicated astro camera, and not a DSLR or mirrorless ?
For good performance of such a wide lens with adapters it will be important for register distance to be exactly the same as on the DSLR. The method I used with my ZWO ASI678MC and longer lenses was to first focus the lens on the DSLR body, tape focus ring so it is not moved, and then mount the astro camera, experimenting with different amount of shims on the adapter until I get good star focus. Once the right amount of shims is found, it can be used with different lenses.
