Weird halo on image (refractor / DSLR)

[GazK]

Taking advice from others on the forum, I'm starting to use Siril. 

When I first hit "autostretch" on my image I get this weird circular halo. It doesn't matter too much on this image as I'll crop in, but on others e.g. starfields, it will.

Optical train is WO Zenithstar 71 > 2" to 1.25" adapter > 1.25" T-adapter > Canon 80d

What could be causing this?

[Snoani]

The stars also look stretched in the corners.  Are you using a field flattener?  

[AstroMuni]

20 minutes ago, GazK said:

When I first hit "autostretch" on my image I get this weird circular halo.

Do your flats have this halo too?

[alacant]

1 hour ago, GazK said:

What could be causing this?

Hi

The reduction to 1.25"

Use 2"/m48 connections throughout, a field flattener and take flat frames.

Cheers

Edited March 4, 2022 by alacant

[Adam J]

On 04/03/2022 at 20:08, GazK said:

Taking advice from others on the forum, I'm starting to use Siril. 

When I first hit "autostretch" on my image I get this weird circular halo. It doesn't matter too much on this image as I'll crop in, but on others e.g. starfields, it will.

Optical train is WO Zenithstar 71 > 2" to 1.25" adapter > 1.25" T-adapter > Canon 80d

What could be causing this?

Its being caused by the 1.25 inch adaptor. Its too small for the setup. 

Adam

[GazK]

Thanks to everyone who responded - no I'm not using a field flattener. About to hit "buy" on one to remove both the halo and the blurry stars.