Flat Field

In taking Flat fields do you use a short exposure or do you take them like you would in taking a dark fied in DSS?

Thanks for any info
Gary

The exposure for a flat field is what is necessary to get a nice histogram without blowing the highlights and without underexposing. It's kind of like a daytime picture. Get the histogram in the middle and you're set. Usually the exposure is between 1 and 20 seconds depending on the amount of light, f/stop of the telescope, ISO setting, etc...