Since flat fields are a source of Gaussian noise (in particular when poor flats are used), the subject of how professional astronomers perform flat fields cropped up.
Olivier Hainaut wrote.
Quote:
Typically we use twilight sky flats - that's the standard.
Dome flat are used only when TwiFF are not available or as part of a more advance FF technique.
The best is to combine Dome FF, TwiFF and night sky FF (ie using deep images on ~empty fields) -
the Dome FF have ~infinite signal-to-noise ratio, but very poor representation of the illumination; the TwifFF have decent S/N; the night FF have the best representation of the illumination, but have poor S/N. Using some techniques like wavelet filtering, one can extract the S/N from the DoFF, and combine it with the illumination from the TwiFF and the NiFF. Using that, you can flatfield at the 99.99% level. Of course, one needs that level only for specific cases; in most situation, 99% is more than enough.
Cheers
oli
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