Dear all,

I am using a Skywatcher 420 t2ED scope for my imaging. The chain from the scope to the camera is like this:

Skywatcher AP 72/420 Evostar
—> Skywatcher Reducer/Flattener 0,85x
—> TSVF208 = 8mm
—> TSM54a-M48i = 1.5mm
—> Pegasus Falcon Rotator = 18mm
—> M48Abstimm05/Ring = 0.5mm
—> M54a-M48a (Pegasus adapter) = 2mm
—> Filterdrawer TSFSLM48 = 18mm
—> M48i-M48i = 0mm
—> ASToptics Adapter M48 Male to M42 Female - (5MM) = 0mm
—> ASI 183 = 6.5mm

It is not exactly 55mm, but very close (54,5mm).

When I take flat frames, I end up with images as the attached one. Unfortunately, the circles are also pretty much present in the final images when I processed them with Pixinsight. I cleaned all devices (whereever I could reach them) properly. This didn't change anything. I pulled out the single components one after the other (my first idea was the filterdrawer, but that didn't change anything) and the problem is still present.

Does anyone have an idea what is causing this?

Kind Regards

Ralf.

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