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The shutter speed is only relevant in that with some cameras if the exposure is under about 3 seconds you can see the leaves of the shutter in the image.
Over about 3 seconds you can't.
With KAI series chips with the right controlling software you can use their electronic shutter in video mode for flats. Apparently it works well and is very fast for daytime flats with a white T-shirt.
SBIG cameras have a different shaped shutter which looks like a bar with a flare at each end and it spins.
This does not seem to show up like leaf type shutters seem to.
I can't comment on a QSI as I don't know what type of shutter it uses.
I find between 20 and 30,000ADU is a good level for flats and take darks same temp and subtract them from the flat when making the master flat.
What I do is take them during the day in my observatory which is painted matt black inside and a bit of light filters in through the gaps and I put a white T-shirt over the lens. You get used to what a flat should look like.
An accurate flat should be taken with the scope in focus, in the same orientation as your light exposures and same setup and I usually take 3 each of flats and their darks for Luminance, Ha and RGB. I used to do separate RGB filter flats now I just use one, usually the red filter. It seems to work fine.
If you darks don't match you light exposures precisely for both temperature and exposure you will get bum flat reduction on a sensitive image. So if your flats aren't "working" then look to how good your darks are first.
Greg.
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