GT_EXPDUR will calculate the effective exposure duration
(not the commanded DPE) of a series of images given an
index structure to work with. You can get an array of
exposures (exps) in msec by typing one of the following. In
the second example, it returns the shutter duration (which is
also the CCD integration period). For dark images the value
returned is the number of milliseconds the CCD integrated for
which is in multiples of 8 msec (8 msec is the minimum for
dark current images).
IDL> expos = gt_expdur(index)
IDL> expos = gt_expdur(index, /shut_dur)