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Old 13-02-2017, 05:47 PM
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Shiraz (Ray)
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Shiraz is offline
Join Date: Apr 2010
Location: ardrossan south australia
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Originally Posted by sil View Post
The maths in that article is a bit beyond me but its totally believable. My own imaging is limited and I can't get to use gear like others here use (and gear I own too). Anyway the lumpiness is definitely a resolution artifact and its there, its not noise to overcome in processing. So when I was imaging with shorter focal lengths I could capture faint fuzzies which sort of looked lumpy or grainy at their small size on the frame (these are things that weren't my primary imaging target that happened to be in the field of view. but the lumps resolved to structure when I imaged at a longer focal length and now it had a similar sized lumpiness at what I thought might be smooth signal. Like looking at a photo of a beach looks smooth, but you go there in person and footprints etc are now obvious but still there is smoothness there until you lie down with a magnifying glass the smoothness gets lumpy again at the limits of the resolution of your eyeballs or camera. its the fractal nature of the universe. So yeah you shouldn't crop your signal to get a smooth background.

I made a shot of the southern cross which almost looks like snow because I pulled up so many dim stars which are really there. Even stellarium etc has limits on the magnitudes it can show you and as the Hubble showed us, no matter how empty a patch of sky looks, there is stuff there. its not a flat even black, so yes I'd expect to perceive some unevenous to all parts of an astrophoto. If you zoom in you can tell the difference between blotchy signal and chroma/lum noise. It helps having a good monitor and being conservative when processing to avoid clipping anything if possible.
I think we all may have seen the effect - I like your beach sand analogy.

fwiw, from some skim reading, found one paper showing how this effect could allow Hubble to probe galaxies as far away as ~300MLY and another showing how information could be extracted on deep unresolved background galaxies using the statistics of sky surface brightness fluctuations in images from ground-based telescopes.
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