A method and an apparatus for examining a sample by means of mass spectrometry. The effects of birefringence, which are detrimental to the image quality, are reduced if the lens axis of the crystal lens is oriented substantially perpendicular to the {100}-planes or {100}-equivalent crystallographic planes of the fluoride crystal. Each of the first plurality of polygons comprises at least one outside edge approximating a straight line within a first flatness tolerance. 0 nm, or Hf at a film thickness of not less than 0. A method of telecommunicating, including video visitation, via the system is also disclosed. In part, these determinations are based upon an algorithm that calculates the relative size of the ducts leading to each of the zones.