Quote:
Originally Posted by Slawomir
Just going purely from theory, or at least from what I think makes sense, is that Luminance collects more photons from the target per hour of exposure (given the skies are sufficiently dark) than RGB filters that block a significant portion of the signal from a given dso, therefore I would go with as much Lum as practical to maximise SNR at the expense of less time dedicated to RGB filters.
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What you’re saying here is true, luminance does capture a much stronger SNR in the same amount of time as RGB; but this isn’t the whole story.
LAB mode allows for a luminance and two chrominance channels. In my tests I replaced the LAB luminance with a true luminance, recombined the LAB into RGB and then checked the noise levels of RGB (2 hour each), LRGB (1.5 hour each), 3LRGB (3 hour L 1 hour RGB) and found that, at least in shorter integrations (6 hours) a pure RGB had less noise.
The caveat of this is that 3LRGB was deeper than LRGB which was deeper than RGB. The increase in depth wasn’t hugely significant in the field I was working with which had no IFN but also had very little above Mag 17 and had galaxies showing around the Mag 21-22 Mark.
Without doing some more testing I would suggest that RGB is better with shorter integrations (<10). LRGB for the medium (10-30) and 3LRGB for the long integrations (thinking Rolf here).
I’d say that after 10 hours per channel of RGB you’ve hit the SNR wall and luminance becomes the best way forward from there.