Quote:
Originally Posted by pvelez
I'm now playing with shorter and longer exposures to get the ADU count away from the 20,000 threshold I've been using so far.
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Pete,
Where did you get a target ADU of 20,000 from? The full well depth of the SBIG 8300 is only 25,500! This may explain the over correction of the light frame data as I previously noted.
Go on the 1/3rds principle (~30%);
25,500 / 30% = 7650 target ADU, so round it up to 8000 and accept a difference of +/- 1000 ADU. When you combine a series of flat subs, data rejection with clip the highs and lows (extremes) and level the data (assuming you don't use sum!!). Average or median combines will work well, if you want to get fancy, CCDStack's clip min/max or poison sigma reject are great. If you're finding that its not correcting the frames well enough, increase the principle to 35%. Just set the target in SkyFlat assistant and let it work out the optimal exposure time. Too easy.
Quote:
Originally Posted by pvelez
If I am binnng at 2x, do I need to target the ADU for a flat at half what I target for 1x binning? So if my target is 20,000 ADU, do I reduce that to 10,000 if I am binning 2x?
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No, target ADU remains the same, its just that the exposure time to reach it will be shorter.
Cheers