I don't personally believe modern CCDs vary too much in sensitivity across the sensor.
Perhaps there is some variance with different coloured lights but again its not the main thing you are trying to correct.
Its usually dust bunnies and vignetting from your scope you are trying to correct.
Some scopes have hot spots/bright centres plus vignetting. This is becoming more common with the use of correctors on RC, Dall Kirkhams etc.
They become more of a challenge for flats I find.
I also find high quality darks and bias essential for a good flat correction on these types of scopes.
APOs are a piece of cake, its the ones with correctors that are tough.
Greg.
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