def compute_texptime(imageObjectList):
    """
    Add up the exposure time for all the members in
    the pattern, since 'drizzle' doesn't have the necessary
    information to correctly set this itself.
    """
    expnames = []
    exptimes = []
    start = []
    end = []
    for img in imageObjectList:
        expnames += img.getKeywordList('_expname')
        exptimes += img.getKeywordList('_exptime')
        start += img.getKeywordList('_expstart')
        end += img.getKeywordList('_expend')

    exptime = 0.
    expstart = min(start)
    expend = max(end)
    exposure = None
    for n in range(len(expnames)):
        if expnames[n] != exposure:
            exposure = expnames[n]
            exptime += exptimes[n]

    return (exptime,expstart,expend)