John, its worse than that.
Originally Posted by John Koehrer
Once upon a time there was a photography magazine called Modern Photography. MP ran educational articles on roughly a two year cycle. Every other year they published a piece, with fairly carefully done tests, on the question "Extension tube(s) or closeup len(es), which is better?" And every two years they reached the same conclusion. Some lenses perform better closeup on tubes, others behind a closeup lens. If you want to know which to use with your lens, try both.