Follow the manufacturer's instructions to evacuate the electron column, optimize the high tension source of the electron microscope, and produce a stable beam of electrons aligned along the microscope's optical axis. (See References 1, 2 and 3)
Increase the lens current through the microscope's electromagnetic coils slowly until an image forms on the fluorescent screen. The electromagnetic coils serve as magnetic lenses in an electron microscope and are used to select the magnification and focus the electron beam. The increase in the coil current results in an increase in magnetic field strength of the electromagnetic lens. The greater the strength of the magnetic field of the lens, the more the lens is able to bend the electron beam away from the optical axis.
Focus the image by increasing the lens current which decreases the focal length of the electromagnetic lenses, or by decreasing the current to increase the focal length. (See References 4, pages 157-158) Find the optimum state of beam alignment and image focus by increasing and decreasing the lens or coil current, while gradually decreasing the magnitude of these current changes until the image is focused and centered on the screen. (See References 5)