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[QUOTE=Shiraz;1028469]My understanding of why summed short subs and one long exposure can be the same is that the primary broadband noise is due to shot noise - that comes as part of the signal-plus-background and you get the same number of photons (target, background and noise) in a given period however you choose to collect them. This argument falls over if you have a camera with high read noise - then the read noise can add to the overall noise and make the SNR worse for multiple short subs. However, it is often still possible to use relatively short subs and still keep the total read noise contribution below the level where it makes any real difference.
Something is not right here. The top imagers are going for longer exposures and getting better results. If your tracking can handle it I have noticed for example you start getting dimmer, fainter details when using 15 minute subs versus 10 minutes.
Don Goldman R Jay Gabany both mentioned they are now using 30 minute subs for their imaging.
John Gleason of Ha fame uses 40 minute subs on his FSQ and Ha imaging.
The usual barrier is tracking. Can your setup handle 30 minute subs and still get tight round stars or do they become elongated or even just bloated from the bouncing around from corrections and periodic error?
I plan on going longer (I currently image at 10 or 15 minutes for LRGB and 20 minutes for narrowband) as it seems to me the really faint parts have to get above the noise floor of the system. It has the best chance of being imaged if you go longer if your skies permit it (otherwise you will get an excellent bright image of the light pollution!). I intend tweaking PEC and Polar Alignment and getting large T-point models to make long exposure with tight round stars possible every time.
Greg.
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