a multi - stage cylindrical mirror analyzer incorporates a primary radiation source , such as an electron gun , disposed internally and along the axis of the multi - stage analyzer . the gun includes all of the optical elements for producing a well defined beam , correcting aberration thereof and scanning the beam on a sample . the components of the gun are distributed along the axial length of the analyzer . aberration of the scanned beam due to traversal of a subsequent lense is minimized by placing the pivot point of the deflected beam trajectory substantially at the center of the lense . the greater dispersion of the multi - stage analyzer and the unit magnification thereof permit proportionately greater exit aperture dimensions , whereby a wider field of view may be realized .