Optimal exposure time for dark subs?

[astrovienna]

I've been using 60x20 minutes of darks against 20 minute narrowband lights taken with my (Sony chip) SXVR-H694.  However, I've read that it's better to use fewer darks, exposed for longer periods - say, 20x60 minutes, or even 10x120 minutes - to reduce the read noise impact of dark calibration.  Is there a way to determine the optimal sub-exposure time?  And is more total exposure time for darks always better than less, all other things being equal?

Kevin

[steve71291]

You might look at DarkBiasNoiseEstimator under Scripts/Image Analysis to answer your question regarding quantifying your darks. There are some high powered math papers on the internet which analyze how many darks you need. They suggest you don't need very many to max out. I don't think you will be able to tell any difference in what you have been using. They should be fine. One thing I would suggest, however, is to Blink the darks. I have on ocassion found one that was clearly defective.