centre
                          |
                          |         ________surface________
                          |........|                       |
                        ____    i  |                       |
                       /    \   n  |                       |
       _________      /      \  t  |         _________     |
      |         |    |        | e  |        |  image  |    |
      |  objet  | ---|--- ------r--|--------|   de    |    |
      |         |     \      /  f  |        | l'objet |    |
      |_________|      \____/   a  |        |_________|    |
                                c  |                       |
                          |     e  |                       |
                          |........|________sensible_______|
                          |
                       optique