Thaks Rick,
I have taken 15 dark frames, 15 flats and 15 bias.
My flats are showing an average adu of around 23k. maybe a bit high but not enough that it should cause an issue.
I combine then using average combine in Nebulosity to create a master dark, flat and bias
I also tried a sigma combine to make the masters but this made no difference.
if I do a simple test and just subtract the master dark from a single light frame then debayer I can immediately see the histogram is clipped in the dark zone and when i stretch a light frame with dark subtraction vs without there is much more signal in my light frame that has not hard the dark subtraction.
This camera has such low noise that difference between a bias and dark frame is not very obvious.
I will post some links to the raw frames if someone wants to take a look.
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