|This picture shows a LEED optics assembly produced by Omicron (one of the major commercial suppliers of surface science equipment). The optics are mounted on a large flange for attachment to the vacuum system. The grids (which filter out the inelastically scattered electrons) are clearly visible at the top, as is the end of the electron gun which just protrudes through the centre of the grids. The fluorescent screen is hidden at the back of the stack of grids. The sample would be positioned about 20 mm in front of the grids.
(Courtesy of Omicron Vakuumphysik GmbH)