[Slawomir (Suavi)]

Hi all,

While investigating plausibility of galaxy imaging from our heavily light polluted site I looked more closely at acceptable level of noise in featureless background in a master luminance.

It turns out that for sky-limited subs, measured level of noise follows very closely theoretical predictions, in spite of significant variations in sky glare from night to night in my location. The number of subs can be easily estimated with the following simple formula:

Number of subs = [ St dev (background) / St dev (desirable level of noise) ] ^ 2

I propose that an acceptable level of background noise in a master luminance is at or below 10 ADUs for galaxy imaging – or any imaging when we want to pull out faint bits that are just above the background noise.
In my location and with my 4” f/6 refractor at 1.18” pp, during the darkest nights I get St Dev for background signal of about 220 ADUs in a 5-minute Luminance sub. Therefore, to bring background noise down to about 10 ADUs, I need…

Number of subs = [ 220 / 10 ] ^ 2 = 500 5-minute Lum subs, which is about 40 hours of integration. To arrive at this result more quickly, I either need a faster setup or move to a darker location (or both).