Quote:
Originally Posted by Paul Haese
Holy hell. My subs are around 3300ADU so I need 33000 ADU flats. So if I take flats at 30000 ADU I will need 10 flats; is that right? What about if I take the at 26000? Am I to assume it would 13? Confused now.  |
yes, no and no
you need only one 33,000ADU flat for each 3,300ADU light to get 10x. The only question is if you are including the bias in your 3300 for the lights - it will reduce the numbers a bit if you have not subtracted the bias. Regardless, a good enough rule of thumb for your system would be to take one 30,000 flat for every light - it is not critical that you get it exact but err on the "longer" side.
30,000ADU flats are good to get above read noise and below saturation - but you could use other flats if you compensate. For example if you wanted to use flats of 15,000 ADU, you would need twice as many of them as you would need of 30,000 ADU flats. the total ADU in all of your flats just has to add up to 10x the total sky ADU summed over your light frames.
making a few guesses on your imaging system characteristics, you would need maybe 30 flats of 30,000 ADU for each 10 hours of imaging.