Quote:
Originally Posted by Shiraz
Hi Rick
Well that was interesting  . I went back to first principles and came up with what turned out to be a quite straightforward analysis and a simple rule of thumb for flat exposure:
if you want the flat induced noise to be below 10% of the total noise, then the total number of flat electrons must be 25x the total sky electrons. If you want it below 5%, you need 100x.
This is quite different to what I Understand of Richard's approach in that there is no single sweet spot for flats - if you expose longer, you need more flats - if your sky is brighter, you need more flats. Seems to make intuitive sense to me. Next step is to test it out in a model and then with a whole bunch of flats. When I have gone through the reasoning a few times, would be grateful if you would give it a once over before I post it (that is, if it holds up under testing - I still reserve the right to be wrong  ).
If this is correct though, the more flats the better and you will always gain something (even if small) by adding flat data. It also means that those who are forced to image under bright skies should stock up on lots of flats. And maybe I can get some better results out of the many sets of lights I currently have by just adding more flats to the calibration pot.
Must also have a look at darks and bias
regards ray |
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.