Best Lenses for Astrophotography

During lockdown I've been reacquainting myself with astrophotography using my K3II. I use the camera's built-in Astrotracer function, which is very good for shorter focal lengths and also a Skywatcher EQ3/2 tracking mount for my DA*300mm f4 lens that gives great results, even with the x1.4 converter. However, I've been disappointed with my DA*16-50 and my DFA100mm macro lenses that both show quite a lot of distortion of the stars (not star trails), i.e. bloated and non-round shapes, particularly away from the very centre of the frame. I wonder what other users have found?
Cheers

Apparently the Samyang 135/2 is a great choice for astro. I know it's insanely sharp from wide open although I haven't used it for astro myself. I've used the Samyang 85/1.4 with good results too.

The D-FA 50/1.4 was decent-ish too.

Here's a very early shot using the Samyang 85. It's not great around the edges but I can't remember whether that's down to movement or distortion (f/2..

Yes, I've heard that the Samyang 135 f2 performs well but I was hoping to avoid spending £430! I've been looking at Pentax 135 f2.5 secondhand but they seem to have mixed review for astro.

I've used that one too. The few shots I have are unprocessed DNG files probably from testing but they seem to show coma and CA. I'm not sure whether it was wide open or not either