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18 months ago I had a conversation with Martin Pugh about how much integration was needed for any particular image. His opinion has proven right as far as I am concerned. He said nothing under 20 hours. 30 is better. Also image subs longer to go deeper.
I sort of knew this from taking long subs several years ago for many of my deep sky images. For some reason I started following what many do here with 10 minute subs. Now with a narrow aperture this just does not work. It resulted in images with lots of integration but not smooth. I had to stretch the data too much to get the brightness that I wanted and that resulted in lots of uncontrollable noise. Longer subs gives me a better signal to noise and a background ADU over 1000. If you have a wider aperture with a fast f ratio you can use shorter subs to achieve the same result. The point being you need to experiment a little to find what length sub produces low noise with high signal and that will mean it will be different for many objects as each has varying dimness.
However, back to the central issue, is that longer integration time means smoother images. I have found colour data has to have a minimum of 3 hours in each filter, so I don't have to use smoothing. 4 hours works really well. Add the lum or narrow band of 10 hours and you are in the 20 hour mark.
Bottom line for me is the quality I am trying to achieve. Going automated has helped to gather lots of data. So I will stick to what Martin said and aim for that each time and try to be patient.
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