LDN-1235. Shark.

And why are you so fixated on the gray zone? It's pretty clear it's an error, but no, you have to make a sarcastic remark. The distance to the sensor is perfect now; the stars are the correct shape across the entire APS-C sensor. I'm seeing this for the first time.
The halos are caused by internal reflections within the glass of the camera's protective window or a filter, which might not have been tested or intended for fast optical systems at all. Here's a good example in this thread.

I wrote the first lines in a fit of groundless indignation, and after five minutes it already seemed rude. I apologize. I've fixed the light pollution zone.

https://www.cloudynights.com/topic/918216-rasa-8-for-eaa-the-learning-curve/page-2

I'm asking about something else. Is it possible to somehow position the filter at a different distance without changing the working distance, for example, by separating the sensor and the filter as much as possible?

Thanks for the advice! Changing the distance might not be possible—there's a 25mm segment, and 17mm of it is taken up by the camera. I came up with a design, with help from Saturn on the forum, that allows a filter to be installed.

Yes, I read the same thing in the article linked above on Cloudy Nights.
The rays from the spider vanes—I printed a diaphragm-cable organizer like this: https://www.thingiverse.com/thing:5513563/files
Just slightly modified, with the aperture stopped down to 180mm.

Regarding the halo - the Astronomik L2 filter will arrive by August, I'll try it out then.