def image_stack(flist, stub, output = 'imstack.fits'):
imlist, junk = parse_filestring(flist, stub)
imlist = [x.fitsfile for x in imlist]
comb = medcombine(imlist, outputfile = output)
tmp = FitsImage(output)
tmp.flist = flist
tmp.header['FILES'] = flist
tmp.update_fits(header_only = True)
return tmp
