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My impression from using the ASI294MC for about a year is that in practice it isn’t working like that. Unity gain has proven to bring out faint detail better using the same sub lengths as before, where zero gain previously showed better star colours on brighter stars but the subtle stuff visibly lost out.
The way I see it is this. 14 bits to 16 bits for the fits file, fine. Multiply it by four to fill the data set, you can rebuild the original data by simple division. The issue is that reducing gain to fit the dynamic range of the sensor into a smaller ADC range is reducing resolution to fit the data in. On the ASI294 at zero gain effectively only every fourth electron is recorded, similar to dividing the output excepted that you can’t multiply by four to get back to what the sensor read was. Every ADU count carries uncertainty of up to four electrons and that information has been discarded.
IMO, only recording every fourth electron to fit the range of the ADC is very much the same effect as having an ADC which can represent in discrete steps every electron each pixel can carry but having a less efficient sensor that records less of the photons striking it.
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