I just bought the tamron 17-70 2.8 for my apsc camera and when I photograph the stars I notice some weird artifacts.

When I up the dehaze to exadurate them the lens loses contrast in like a semi circle pattern at the bottom of a vertical image aswell as it seems like the lens isn’t covering the full apsc image circle. There corners seem to be experiencing some sort of darkness because of that. It’s not any filter that I had on because even with and without filter the bad vignetting is still there.

Does anyone know if this is like a know defect of the lens, or if my particular lens has a defect?