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Great results Paul. I agree with Mike, 25 minute subs is a bit of tough one.
I cut my subs back to 10 mins as I got rounder stars. 25 minutes will show up any slight error in your polar alignment as even though you are autoguiding it won't compensate for rotation from polar alignment errors.
Also flexure is more likely to show up in longer exposures -gusts of wind, stray clouds, etc etc.
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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