Charged particle spectrometers

An electron spectrometer comprising a hemispherical analyzer, means for irradiating a sample located in a sample position to cause electrons to be emitted therefrom, an electron optical lens system which includes a plurality of lens elements and electron deflection elements defining at least two stages of deflection for receiving the electrons emitted from any desired position on the sample and delivering the received electrons to the analyzer, a detector connected to the analyzer to detect analyzed electrons and energizing means for applying potentials to the elements such that electrons which are ejected from a restricted selected area of the sample are brought to a focus by the lens system, and wherein the electron optical lens system includes at least two spaced apart mesh elements at the entry to the lens system, the mesh elements being concave toward the sample position so that aberrations of the lens system can be reduced and the energizing means in a first mode apply a first set of potentials to the lens elements and deflection elements such as to retard electrons passing between the mesh elements to effect refraction of the electrons in such a way as to minimise the aberrations of the lens system and permit collection of the electrons emitted over a wide acceptance angle from a selected area of small dimensions (viz. less than one square millimeter) and at any desired position on the sample and to provide high magnification, and in a second mode apply a second set of potentials to the lens elements and deflection elements so as to accept electrons from an irradiated area which is many times larger than for the first mode, and means for switching the potentials on the lens elements and on the deflection elements to switch the spectrometer between different modes of operation without mechanical modification of the lens elements.