Quote:
Originally Posted by tonybarry
So for an exposure which nets you 10 photons, shot noise on one exposure might put that up to 12 the next time, or down to eight the time after, say a twenty percent change.
For an exposure which nets you 10,000 photons, shot noise will put that up to 10,002 ... which is close to zero percent.
Regards,
Tony Barry
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Shot noise depends on the photon influx in a simple way. If your average signal is N photons, the shot noise is sqrt(N) photons. When you gather more photons, the shot noise increases, but the important fact is that the signal increases faster, so the signal to noise ratio goes up. Gather on average 100 photons per sub and the shot noise will be 10 photons (square root of 100). The SNR will be 100/10=10. Gather on average 10000 photons per sub andthe shot noise goes up to 100 photons. The SNR will be 10000/100=100. Your SNR is 10 times better with the longer sub.
Just for the record: if the "true" signal is N photons, then saying the shot noise is sqrt(N) means that you can expect 68% of your subs to have values between N+-sqrt(N) and 95% of your subs to have values between N+-2*sqrt(N).
Geoff