Image artefact after ABE

[philh]

Im having a problem with my imaging. When I apply the automatic background extracter (ABE) I got some pretty horrid image artefacts. I have tried doing similar things in other programmes and cant replicate the artefacts. Any suggestions?
Im using a zwo1600 colour cooled camera on 8 inch cesltron SCT with hyperstar
This image is a single frame

[RickS]

There's a good chance that the artefact is in your data but hidden until you remove the background.  Are you doing flat calibration?  Have you tried DBE?

[philh]

In this case, i did not use flat calibration as my aim is to try and show people a deep sky object in the time it takes to capture an image ( say around 30 secs to a minute) open it pixinisght and then run the ABE and a stretch. Having horrid image artefacts takes away from that sense of wonder I was hoping to generate.
When I have used flats I still get bright patches like the one you see in the middle. I tried the DBE but didn't see any change although Im not familiar with it enough to really push it and see if I can get the affect i want without the artefact.

[RickS]

In this case, i did not use flat calibration

Then the underlying source of the artefact is almost certainly the scope/camera system.  ABE is merely revealing it.

When I have used flats I still get bright patches like the one you see in the middle.

I think you need to fix your flat fielding process.  A very fast system like Hyperstar will have a steep light cone and that will make flat fielding more challenging...

Cheers,
Rick.

[philh]

to take flats I held up an Led  screen against the lens until I had the desired brightness value. What else should I be doing?

[RickS]

to take flats I held up an Led  screen against the lens until I had the desired brightness value. What else should I be doing?

There are a lot of things that can and do seem to go wrong with flats.  I generally like sky flats but they can be difficult to do well without automation and aren't always convenient.  I have also had some success with light boxes and EL panels but I don't feel that these flats calibrate the lights quite as accurately.  Perhaps I should do some measurements and see if this is real or imagined...

You can find lots of advice on flats with a web search so I'll just confine myself to mentioning some potential pitfalls.  The hyperstar protrudes from the front of the scope.  Are you using a dew shield to keep out stray light and keep the "Led screen" parallel to the corrector plate?  Are you sure that your Led screen has reasonably uniform illumination?  Does it have a reasonably broad and even spectrum?  Are you taking very short flats?  The ASI1600 sensor does some weird stuff with subs of a couple of seconds or shorter so it would be wise to do flats longer than this.  Are you making sure that you're not exposing beyond the linear range of the camera?  Are you using a UV/IR blocking filter?  I'm pretty sure that the ASI1600mc camera window is AR only, so you really need one.  Do you have anything shiny/reflective in your imaging train?  If you don't have a blocking filter you may find that something that looks perfectly black visually is actually reflective in IR and causing havoc with your flats.

Cheers,
Rick.