[Quark (Trevor)]

Hi All,
Have never taken any flat frames before. I have "Introduction to Digital Astrophotography" by Robert Reeves, which talks about the need for flats and what they do.

I intend illuminating a projection screen in front of my scope, at least initially, to take my flats.

My question is how do I work out the length of exposure for my flats. I have seen write ups suggesting 2 to 10 secs, but what determines the time, how will I know that I have selected an appropriate exposure?

Also, do I need to take darks the same length of exposure as the flats to create a master flat?

Regards
Trevor