Originally Posted by Jon Ruyle
Yes I do use the autoguiding even for wide angle exposure that long. The CG5 GT mount isn't that accurate, especially when you overload it like I do. And no mater what camera and lens I use it does make a difference in the stars
Why bother with long exposures? Increased image data / SNR.
Stacking multiple exposure gives you a better SNR, but it doesn't necessarily increase your exposure / saturation. Stacking multiple longer exposure will result in a better image than stacking multiple shorter exposures or a single very long exposure.
An assumption that many people make is that if you stack 40 x 30 second exposures that it will equal a 20 minute exposure. When in fact what you will have is a cleaner looking 30 second exposure instead. Don't get me wrong, more exposure will gain more detail than a single longer exposure, but only because you are improving the signal to noise ratio.
This thread can explain it better than I can here.
SNR and Total Signal
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