I use Artemis capture and a white tea towel over the telescope an hour before dusk.
In Atremis capture I use an exposure of 0.4 seconds, do one capture, then hover the mouse over the centre of the capture. On the bottom right hand corner, is a number that changes from 0 to 65536 when you move the mouse.
I adjust the exposure time until the centre of the capture reads about 32000.
Flats solved all my vignetting problems on my Atik 314ec.