Gain Mis-match Warn...
 
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(@tommohawk)
White Dwarf Customer
Joined: 2 years ago
Posts: 14
October 11, 2021 12:20  

Seems to  be some debate about whether gain for flats needs to match gain for lights - in my view not, although APP flags a warning about this. Fair enough to point that out or any other potential issues. Trouble is it doesn't seem to flag it at the outset - it waits a while which is a pain if you hit the integrate button to do the whole process and come back hours later to find it's interrupted with a warning.

Summary - could all warnings be made at the outset, rather than part way though processing?

Thanks Tom C


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3961
October 11, 2021 16:45  

Flats need a proper illumination of your sensor, through the optics of your setup to be able to correct for vignetting (and dust). These are characteristics of the setup and that data isn't something that needs to match regular astro-images and calibration data. You can set the gain to 0 (for max dynamic range) and take 1-2 second exposures that will have the linear histogram land at about 60-70% (the only thing is that you shouldn't clip the data to the right, the 50% you see quoted a lot isn't important). The flats do need their own calibration data, dark-flats and these do need to be at the same gain etc. as the flats.

Could you post a screenshot of the warning as I can't remember it does that, in my view it shouldn't be about having that match with the lights...

 


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(@wvreeven)
Quasar Admin
Joined: 3 years ago
Posts: 1226
October 11, 2021 20:16  

To add to what Vincent wrote: the gain of the flats does not have to match the gain of the lights. Neither do offset, temperature and exposure time. However, the flats do need to get calibrated and for that either bias and darks or dark flats with the same gain, offset and temperature are needed. In case of dark flats, the exposure time needs to match as well with the one of the flats.


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(@tommohawk)
White Dwarf Customer
Joined: 2 years ago
Posts: 14
October 14, 2021 11:25  

Thanks guys. We are all on the same page with regard to flats then - important thing is to make sure that the settings for the flats match  the setting for the dark flats. And also as you say to ensure working on the linear part of the sensor.... which is something I've only just realised after 4 years of problematic flats!! It seems that setting the average ADU of the flats to match the average ADU of the lights may be the surest method. (For my ASI1600 cool at least)

Re the APP error message, which was the main point of my post - I did one re-run and it seemed fine so maybe I just did something wrong. If I get the same issue again I'll post back.

Thanks for the feedback - what a great forum!

Kind regards

Tom


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3961
October 15, 2021 14:30  

Thanks so much for appreciating the help! 🙂

Yes, looking at the ADU is a good way to check if you're aiming for a good value. Glad it helped and I hope the processing is going better now?


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