An Electron-Lens For Opaque Photocathodes

For many years image tubes have been made which use semitransparent photocathodes to conveniently separate the optical and electro-optical functions. It is now possible to employ opaque photocathodes in image tubes having a special electromagnetic lens, without the use of special internal image forming optical lenses or mirrors. The design of this special electron-lens and measurements of some of its characteristics are discussed in succeeding sections.