Quote:
Originally Posted by gregbradley
I don't think there is any difference between 2 x 10 and 1 x 5 stacked and 1 x 25mins in terms of signal to noise ratio. It is more a thing in narrowband to do long subs as the signal from those are so low that it is hard to get above the noise hence longer subs.
Greg.
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For ABG there is quite a difference - regardless of filter. Remember, today's sensors respond to light in a linear fashion. The longer you go, the more light collected. So for the dim regions of an image, a single 30min long sub will give you a better S/N ratio than taking 3 x 10 min subs. Also, the latter doesn't make an image any deeper. You're still only collecting 10mins of light, thus noise will continue to reveal itself in the dim regions when you stretch it hard to get out the faint nebulosity. Clearly, the issue with one sub is that you've got some work to do in removing chip defects, cosmic ray hits, etc, so obviously more subs the better to reject the outlier pixels. You can measure the ADU levels to confirm the theory. The recent DSLR images presented on this forum attest to going long - stunning results indeed.