Quote:
Originally Posted by RickS
That appears to reflect my recent experience, Ray. I'm away from my scope and data for a few weeks but will do some experiments when I get back. I look forward to your results...
Cheers,
Rick.
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Quote:
Originally Posted by gregbradley
There is a natural limitation of how many flats you can get if you take dusk/dawn flats. That is how long it takes to expose, download and save in rapidly changing light conditions.
This would also be an argument for using artificial light flats as there is no rush.
Greg.
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Quote:
Originally Posted by Paul Haese
Hmmm ok, will give that a go. I usually use around 7 or so flats on the RC12. This has been largely a guess. So I will get a bit more precise about this and work out the numbers required. On the TSA I have been using 16 flats on each filter.
These days I tend to do flats on the single colour I am imaging that night.
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thanks for the feedback and info.
Reworked the theory and will attempt to validate it tonight if all goes well - will start a new thread, since it could possibly be useful to others who might not read this one.
Looks like you can control flat-induced noise simply by making sure that you have at least 10x as many total flat electrons as you have total sky electrons. eg, if you take 100 lights where the sky background in each is 3,000ADU above the bias, you need to take 100 flats if you use 30,000 ADU flats. It has nothing to do with how many subs - just how many electrons - so if you took flats with say 10,000 ADU in the above example, you would need to take 300 of them. If you image for a long time, take a lot of flats, if you have bright sky, take a lot of flats.
Not yet sure how much of an issue colour is for noise reduction - guess that dust on filters might make separate flats worthwhile for getting rid of bunnies if that is a problem. Quite a bit of other interesting stuff to look at as well, including the possibility that past images can be improved by using two different sets of flats - one to control noise and the other to get rid of vignetting etc
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Regards ray