A multi-element electrostatic lens was constructed to improve the energy analysis of electrons ejected at zero degree in ion-atom collisions. The lens, coupled to a cylindrical mirror analyser, considerably extends the energy range of the analyser to lower energies by acceleration of the electrons, and improves its angular resolution by angular magnification. The distribution of the potential in the lens was determined using series expansion, starting from a given function of potential at the lens axis. The electron-optical properties of the lens were obtained from ray tracing. The power of the lens is demonstrated taking the spectrum of electrons emitted from He - on Ar collisions at 112 keV impact energy, in which the auto-ionization peaks originating from the (1s2p2p') 4P e shape resonance of He - are completely resolved.