1. K.R. Spangenberg, Vacuum Tubes (McGraw-Hill, New York, 1948)
2. J.A. Simpson, C.E. Kuyatt, J. Res. Nat. Bur. Stand. 67C, 279 (1963)
3. J.R. Pierce, Theory and Design of Electron Beams (D. Van Nostrand Co., Inc, New York, 1949)
4. F. Rosebury, Handbook of Electron Tubes and Vacuum Techniques (American Institute of Physics, New York, 1993)
5. A particularly excellent account of practical aspects of electron optics is given in J.H. Moore, C.C. Davis, M.A. Coplan, Building Scientific Apparatus (Addison-Wesley, Reading, MA, 1983), chapter 5