Quote:
Originally Posted by Shiraz
just tested another dataset with 16 very similar calibrated subs. the noise in a few subs chosen at random varied from 4.55 to 5.5 with a mean of about 5. A stack without any rejection produced a noise level of 1.24, which is almost exactly 1/4 of the average sub noise levels  as it should be for 16 subs. I am not seeing any gain at all over the expected sqrt(n) due to alignment before stacking.
ie, I get Stacknoise = Subnoise/sqrt(n)
A stack of the unaligned subs had noise about 25% higher than that from the aligned stack  assume that this indicates some residual FPN.

That makes sense, Ray. Shot noise imposes an upper bound on SNR and the best you can do is minimise the effect of read noise, thermal current noise and FPN.