Thanks Skywatcher, but please, write in english or chinese. ;)
I neglicted the offset subtraction. Since the offset of the ASI120mm is quite low, it doesn't really matter (for this kind of images).
One dark frame is acquired at the beginning of the capture with FireCapture (which asks to place the cover onto the scope, then to remove it after the dark is acquired). Then FireCapture automatically subtracts the dark from all of the images during the capture. You have just to take care of the temperature gradient during the session. It decreased from 15°C downto 12°, and the signal of the dark was too high in the last frames (dark spots in the raw images). The stacking process dimmed this drawback. Perhaps, in the future, ZWO will add a small regulated TEC...
I took 170 TIFF images (16 bits), then stacked them with DeepSkyStacker.
I'd rather take and subtract a flat, too... But that's a first try.
Nicolas.
