Quote:
Originally Posted by Merlin66
... The shot noise contribution is not IMHO affected by the use and summing of subs. The total signal determines the shot noise.
Data of 100,000 photons will have a shot SNR of 316 whether it came from 1 or ten subs. ...
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Totally agree. Never said anything to the contrary. Completely obvious.
Quote:
Originally Posted by Merlin66
... (The SNR comments above are based on the original post by Placidus:
3) All else being equal, then for the very faintest targets, the snr is proportional to exposure time T, but proportional only to the square root of the number of subs N. That means that for very faint targets, it will be hugely better to do ten 3600 second subs than 36,000 one-second subs. It will be better by a ratio of 3600 root(10) to 1 root(36000), or a ratio of six to one. Long subs rule.)
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Merlin, are you agreeing or disagreeing with my statement 3?
You
seem to be disagreeing on the grounds that the partitioning of shot noise into many short subs does not affect the signal to noise ratio. That is like saying that since tables have four legs (true), they cannot be used for serving food. Your true statement does not disprove my true statement.
Partitioning the same total exposure into a large number of subs increases the snr by adding many doses of read noise instead of just a few doses. The equation that I gave (for the case of no dark current noise and no sky noise) demonstrates that. It is still the case with the more complex equation that adds in the role of dark current noise and sky noise, although the effect is less or much less in sky limited shots.