What type of aberration is this?

[MartinFransson]

I´m still working on sorting out possible tilt and other issues with my TS Photoline 80 f/6 APO. I´ve experimented a bit with backfokus distance (from 122 to 125mm). Ackording to TS the flattener (TS 2" flattener, no reducer) is supposed to be at 123mm from the sensor. I don´t see much difference when altering the distance a few millimeters.

However, I´m starting to wonder whether this is tilt, spacing or something else. The "flaring" of stars in the corners does not indicate wrong spacing, does it? Changing the focus in and out makes the stars a bit better but not perfect.
What kind of aberration would cause this star shape? It is most obvious on the S2 data (which might not be 100% in focus). Also, never mind the slight trailing on the stars in the whole images, I was shooting almost at zenith so the tracking was a bit so so.

Could it be that the TS flattener just is not better than this?

Images in order:
Ha = 3nm Astrodon
O3 = 3nm Astrodon
S2 = 8nm Baader

Camera ASI1600MM-Cool

Edited August 29, 2020 by MartinFransson
Added image info

[Adam J]

looks like too much spacing on your corrector to me.

Also maybe the corrector is introducing some CA, you can tell lots by looking at the indevidual RGB channels.

Edited August 29, 2020 by Adam J

[MartinFransson]

11 hours ago, Adam J said:

looks like too much spacing on your corrector to me.

Also maybe the corrector is introducing some CA, you can tell lots by looking at the indevidual RGB channels.

OK, I haven´t had a chance to do much RGB imaging with this scope yet. But I will look into that.
I might reduce the spacing by quite a lot just to see the effect it has...

[MartinFransson]

On 30/08/2020 at 00:36, Adam J said:

looks like too much spacing on your corrector to me.

Also maybe the corrector is introducing some CA, you can tell lots by looking at the indevidual RGB channels.

Running some test now with 5mm less spacing than what TS states is correct. Just a few test shots but so far it looks better!