I can't comment on any camera I have not played with in terms of what range they can actually produce, my original question really is relevant only to the IMX294 sensor or others like it which may have a big read noise improvement somewhere in the range of gains available.
With just a bit under 2 electrons read noise (Call it 2 for the sake of it) and 65K wells (I can't see any reason to assume sensor well depth is not 65K regardless of gain) is it not reasonable to assume you could make use of 16 bits worth of conversion here?
Put it this way. From my own data it seems that at -15 degrees sensor temp and 300 second exposures, all the sources of unwanted electrons add up to under 1000e, leaving about 64ke of useable
sensor range at the lowest gain that gets you the HGC mode read noise benefit. At the gain that gets the read noise benefit you can only quantize a quarter of the fuull well depth.
A big difference I can see between CCD and CMOS that means I am not sure if you can compare them in the terms done here is the use of anti blooming gates and similar techniques that mean they are not so linear near full well. The dynamic range is effectively reduced to avoid blooming artifacts so the well depth may not compare directly to CMOS wells that don't spill electrons when they are saturated. Another compromise, just a different one.
It is interesting to pinch QHY's blurb on their IMX571 based camera (QHY268C in competition with ZWO's ASI2600) It has by their page got read noise between 3.5 and 0.7e and 51ke wells.
Quote:
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The QHY268C is the CMOS camera with native 16-bit A/D on-chip. The output is real 16-bits with 65536 levels. To compare with the 12bit and 14bit ADC. The 16bit ADC can get high sample resolution, system gain will close to 1e/ADU. No sample error noise and low noise.
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I can't quite make head nor tail of the info ZWO have on their site now for their version, it suggest all gains on the ASI2600 will be above unity, from 0.8e/adu to about 0.05e/adu and about 100e (yes, 100 electrons!) wells at that gain! Their suggested gain of "100" where the HCG mode cuts in would seem to be about 4ADU per electron which does not seem right. Time will tell if that gets edited. But it does show nearly two stops more DR than my ASI294 at the gain where the HGC mode starts. It looks like a decimal point might be in the wrong place somewhere.