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Why take flats though?
I can see how they correct for vignetting and dust, but can't see how they help otherwise - flats can also get rid of fixed pattern noise (FPN), but only in the bright parts of the image where it doesn't matter. I am not too concerned that my saturated stars should have high SNR - I want high SNR in the dimmest bits where FPN is negligible.
The example camera in Richard Crisp's paper is an 8300 with a fixed pattern factor of 0.77%. My 694 is a bit under 0.4% (I think). With either of them, according to Richard's data, this level of FPN is not significant until the SNR reaches above about 100. This is way above the ISO standard for "excellent" image quality, so FPN removal will be unlikely to improve in any significant way on what is already an excellent+ image quality .
The human visual system is very sensitive to regular patterns, but if this is an issue, the images can be dithered, which turns the FPN into minor random noise.
As far as I can tell, if the camera has very high FPN, flats could be useful for reducing noise - otherwise they can only really help in correcting for uneven illumination (vignetting and dust). Am I missing something?
Last edited by Shiraz; 10-11-2013 at 07:00 AM.
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