ctions using one iteration of the light time solution
      ----------------------------------------------------------

      When the requested aberration correction is &quot;LT&quot;, &quot;LT+S&quot;,
      &quot;XLT&quot;, or &quot;XLT+S&quot;, only one iteration is performed in the
      algorithm used to compute lt.

      The relative error in this computation

         | LT_ACTUAL - LT_COMPUTED |  /  LT_ACTUAL

      is at most

          (V/C)**2
         ----------
          1 - (V/C)

      which