Thanks Brett.
I measured the RMS variability of the ZWO dark and it is ~12 electrons due mainly to the dark current of about 0.5e/s/p (I had to make of few assumptions here - ZWO has not published a dark current number). That is almost exactly equivalent to a 5 minute dark from your QHY12, which also has an RMS variability of 12 electrons due to read noise. Your darks will not have the pedestal of the ZWO dark, but, when that is subtracted, the total noise will be ~identical for the two cameras. For anything shorter than 5 minutes, the ZWO will be better, but the QHY will always have 12 electrons read noise. At a sub length of 5 seconds (say), the ZWO could have under 2 electrons RMS total noise - this is very close to zero noise and I know of no other affordable camera that even gets close.
ZWO is going to have a problem though, because people are still thinking in CCD terms, where you must have long subs to get over the top of the read noise and that means that you must have deep wells to get around saturation on bright stars. The new CMOS chips will work best with short subs (where the older CCDs are hopeless) and that brings all sorts of advantages including drastically reduced mount requirements, no need for guiding, better resolution and almost unlimited well depth. However, it requires a complete rethink of how one uses a sensor - there will be people who will try to soak the new chips with 20 minute subs and f10 telescopes (like they used to do) and they will not get good results - expect a barrage of "this thing has bad dark current and saturates easily" as people drastically misuse the new cameras.
CCDs still have a place - the old methods still work well. The CMOS cameras also will likely not do quite as well at narrow band imaging, where the higher read noise will be more of a problem. They will also possibly do best with relatively fast scopes (haven't done that analysis yet). However, the new chips offer some very exciting possibilities for anyone willing to experiment with radically new ways of doing things (which will not be appealing to everyone). This really is shaping up to be a revolutionary development, as Emil's extraordinary image shows (see post #18)
