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Compare your ADU values on both of the raw 8 minute subs and see what you get?
Because the moon was gone the skies were darker hence you did not reach your optimum sky background level.
The longest I can go without saturating my background level in adelaide is about 10-15 minutes, where as somewhere like Arkaroola I have to go 45 min or longer depending on the subject.
Your flats are also critical, you have to establish what your optimum background value is based on your imaging scale and your cameras specs. There is a calculator for that on the CCDWare website (Sub Exposure Calculator).
You need to take some test images of an empty part of the sky first with no nebulas or galaxies, then use the values from that image to populate the values.
Flats should be roughly 30% of your Well Depth capacity.
Cheers
Mark
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