function o_make_filename, startname, addition

  ; convert to strings
  startname = strcompress(string(startname), /remove_all)
  addition = strcompress(string(addition), /remove_all)

  ; assume we're passing fits files....last element should be 'fits'
  name = strsplit(startname, '.', /extract)
  len = n_elements(name)

  ; make the filename
  filename = ''
  for i = 0, len-2 do begin
      filename = filename + name[i]
  endfor

  filename = filename + '_' + addition + '.' + name[len-1]

  return, filename

end