Flats problem or something else

[philherbert]

Well I tried to test my first hypothesis (whether there is any stray light in the subs) but didn't end up showing anything useful. I have since been exploring ways of creating a synthetic flat which should at least remove the dust shadows. Still a work in progress.

It shows promise (the dust shadows appear quite well) but it is a pain getting rid of the stars. I'm trying various techniques out but would be interested in others techniques for synthetic flats.

Phil

[philherbert]

I just wanted to close this topic off, in case anyone is desperate enough to read to the end!

I have spent nearly two months trying to sort the problem out, and was starting to question my sanity, but in the end the camera supplier (FLO) were good enough to provide me with a replacement camera to test. I'm pleased to report that the inverse vingetting and curvy lines that were visible in the 'background' of the stacked images have all gone, so I am concluding that there was some kind of problem with the camera (I have been careful to change nothing else in the imaging train or software settings, so I'm 99% sure that this is the case, although I don't know enough about the camera to work out what kind of fault could have caused it).

To be more accurate there remains a little inverse vignetting, but ABE / DBE in PixInsight deals with it pretty well. In the end it was the curvy lines in the background that couldn't be dealt with through any ABE/DBE or alternatives that convinced me that the camera was to blame.

[eshy76]

Hi Phil, this is an old and closed off thread, but it was really helpful to me. Something is not quite right with my LRGB shots on the mono version of the ASI1600 - essentially the backgrounds are brighter than they should be...I think I'm getting the inverse vignetting you were talking about here.

Scouring SGL and CN for a solution, I found comments on CN saying that the bias frames are inconsistent for this camera below exposures of 0.2s...that rings true to me as it has been in my Lum and B integrations where what I thought was light pollution was appearing in the corners - the dark flats I was using for those were really short as in 0.04s...

...my trail of thought is to try to dim the light panel to get flats of more than 0.2s in length or to go back to using bias frames, but which are more than 0.2s in length.

I'll report back if this makes a difference as it may be helpful to you or others, or i will make a new thread if you've moved on from this.