Quote:
Originally Posted by Shiraz
FWIW, suggest that the equation for sky limited imaging is:
SNR = N*Q*T*P / sqrt(N*Q*T*P + N*Q*T*S + N*T*D + N*RN*RN)
where S is the sky signal and D the dark current
the generally agreed setting for sub length is to make N*Q*T*S the dominant term in the denominator, at which point the SNR is independent of RN (ie there is no gain in SNR from using short subs).
Normally, subs will be long enough that N*Q*T*S >~ 10*N*RN*RN - or something similar. ie, N cancels out and the required sub length T scales directly with RN*RN, the same as for narrowband. Since sky-limited exposures with normal cameras come in at 10-20 minutes for a 10e RN camera, an equivalent system with a 2e RN camera could do the same job with 24-48 second subs.
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How do I measure the sky signal for this equation?
I assume the Q figure is different for each channel or narrowband being used?
And for the ASI1600, the gain setting determines the read noise, right?
If I know these 3 things, I can get a good value for T? Then effectively after that, increasing N should increase SNR at nearly the best possible "rate" I can theoretically achieve (for the sky, camera, etc)?
Is this right?