BRIGHTNESS ZOOM-REGULATING DEVICE FOR ELECTRON MICROSCOPE

PURPOSE:To improve the response by finding a constant from the exciting current of an irradiation lens and the magnification of an expansion lens system at a set brightness, and controlling the exciting current of the irradiation lens responding to the variation of the magnification of the expansion lens system. CONSTITUTION:A constant K is found from the exciting current J of an irradiation lens 1 and the magnification M of an expansion lens system 7 by the first operation device 5, and the exciting current J of the irradiation lens 1 is controlled responding to the variation of the magnification M of the expansion lens system 7 by the second operation device 3. As a result, even though the magnification M of the expansion lens system 7 is converted as desired, the exciting current J of the irradiation lens 1 can be computed from the magnification M, and the exciting current J is controlled to obtain a specific brightness. Since the brightness is zoomed only by the operation-process in such a way, the exciting current J of the irradiation lens 1 can be determined instantly without delay. The response is improved consequently.