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For many years I put flat frames in the too hard basket. I never got around to building a light box, etc.
Then I started using CCD Commander. One of it's features is the ability to automatically take flat frames at the time of twilightwhen the sky is not so bright it saturates your camera but is bright enough to not have stars showing through. By this way you get a perfect flat field. Easy!
You don't need to use CCD Commander, it just makes it easy. You point the telescope relatively high in the sky but on the opposite side to the sun (east at sunset, west at sunrsie).
As an example it has calculated that at 6:02 tonight it will start taking frames, and will continue until the brightness count is at my desired level (20,000 ADU).
Roger.
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