Hi
I have an issue where my flats do not seem to be doing their job under specific circumstances. A little background:
I have used PixInsight with data that was obtained with an STL11000 CCD camera and have never had an issue. Every since I went to a ASI6200 monochrome CMOS camera I have persistent issues where it seems that calibration is not working properly and I end up with some residual "donuts" remaining. At first I though this was the filter wheel and therefore changed the filter wheel to another better make. No difference.
I use a light panel for the flats and take dark flats. I do not use bias frames. These are the observations:
Each individual calibrated sub shows no indication of any issue with calibration. I can stretch the heck out of it and it is clean.
Integration of the subs however will show that the flats are not doing their job if an ABE or DBE is done on them.
With narrowband data, it is barely noticeable. With RGB data which has many many more subs, it is much more apparent.
I'm really at a loss here but have some ideas of what may be at play but I am not sure.
For the flats, I use Voyagers automated flat mechanism. This will vary the exposure until the resulting flat is around 32768 +- 8%. It will then start exposing the flats, but during the sequence which acquires 30 flats the exposure can change. For example, I may have a 10 second exposure on the flat when it starts and then it might change to 11 or so within that range. I therefore choose an exposure of 10.5 seconds for the flat darks.
Will this potentially cause issues?
I really do not know what to do at this point.
Thanks for any insight.
Tom
I have an issue where my flats do not seem to be doing their job under specific circumstances. A little background:
I have used PixInsight with data that was obtained with an STL11000 CCD camera and have never had an issue. Every since I went to a ASI6200 monochrome CMOS camera I have persistent issues where it seems that calibration is not working properly and I end up with some residual "donuts" remaining. At first I though this was the filter wheel and therefore changed the filter wheel to another better make. No difference.
I use a light panel for the flats and take dark flats. I do not use bias frames. These are the observations:
Each individual calibrated sub shows no indication of any issue with calibration. I can stretch the heck out of it and it is clean.
Integration of the subs however will show that the flats are not doing their job if an ABE or DBE is done on them.
With narrowband data, it is barely noticeable. With RGB data which has many many more subs, it is much more apparent.
I'm really at a loss here but have some ideas of what may be at play but I am not sure.
For the flats, I use Voyagers automated flat mechanism. This will vary the exposure until the resulting flat is around 32768 +- 8%. It will then start exposing the flats, but during the sequence which acquires 30 flats the exposure can change. For example, I may have a 10 second exposure on the flat when it starts and then it might change to 11 or so within that range. I therefore choose an exposure of 10.5 seconds for the flat darks.
Will this potentially cause issues?
I really do not know what to do at this point.
Thanks for any insight.
Tom
