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Old 09-08-2014, 08:41 AM
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RickS (Rick)
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Originally Posted by Shiraz View Post
Thanks Guys.

Rick just pointed out that Stan Moore derived essentially the same equation in:

Looks like I didn't invent anything after all . I suppose one consolation is that I seem to have got it right at least.

Apologies to Stan.

regards Ray
I'd be happy to call it an independent discovery, so still well done, Ray!

Originally Posted by Peter Ward View Post
I've been mulling over this for a time, and maybe this is not correct.

Is read noise fixed or or random? I suspect the latter, and in fact this is exactly what "skipper CCD''s" utilise by being read-up hundreds of times to get read noise to sub electron levels.

Further, if read noise were fixed, you'd see a gradual pattern build up after summing multiple frames. To date, I've not seen that happen even after summing dozens if frames.

Assuming then read noise is indeed random, would not the noise reduce by the square root of the number of subs.
Yes, read noise is random (if it wasn't then it would be unwanted signal, not noise) and its effect on SNR reduces by stacking. However, the whole point of the Stan-Ray rule of thumb is that you can make the effect of read noise inconsequential by making your subs long enough. Then you are only at the mercy of the noise sources you can't control like shot noise from the target and shot noise from the sky glow.

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