Ah, it's logarithmic!  That makes sense!
So each 30 'gain' is a stop, basically. Each 100 gain is ten times brighter (or dimmer).
The gains I've seen ppl using are 75, 139, 200 and 300.
As near as I can tell, gain 75 would correspond to an e/ADU of about 4.8, which means the entire 20,000 range of the wells are distributed across the 4096 possible ADU values.
139 is 1 e/ADU
If I got this right, then gain 200 corresponds to 1024 ADU levels, or essentially a 10 bit image, and gain 300 is somewhere between 6 and 7 bit with only around 100 ADU levels.
I don't suppose I'm going to break anything if I scale my gain settings in db from 139 for exact bits so there's no rounding weirdness in converting from e to ADU's eg; 139, 169, 199, 229, 259, 289, etc
Best and thanks
Markus
