Odd donuts that can't be eliminated by flat

[Ed2000]

Dear all,

I have changed to a new scope (SW Quattro150 F/4) and tried some imaging.

During processing, I have found some odd elliptical donut on the final stacked image. I did flocked the inner surface and covered all light-leaks. Collimated with laser and the stars looked fine.

The first image is overstretched to show donut. The second image is a overstretched flat.

I do need some help. Any comment and suggestion?

 

Edited March 8, 2023 by Ed2000

[michael8554]

Hi Ed

What camera ?

How are you taking Flats ?

1. The Flat seems to be flipped compared to the final image ?

2. Do you have the Coma Corrector ? Reflection from that.

Michael

[Ed2000]

Thanks Michael.

I am using ASI533MC pro with the native coma corrector from SW Quattro 150.

The flat is fine in orientation during WBPP in pixinsight.

I am thinking whether the oval shape donut can be due to stray light. I did not use any dew shield on my Newtonian.