| 摘要 |
PURPOSE:To adjust the amplitude contrast pertinent to a lowly multiplied image to the optimum state by setting the excitation intensity of a focusing lens so that the crossover image of an electron beam is imaged upon a diaphragm installed in back of an objective lens. CONSTITUTION:A change-over switch 11 is provided between the second focusing lens 4 and its power source 9, and the second lens-power-source 12 is connected to the terminal (b) of the switch 11. Next, both the output of a power source 8 for the first focusing lens 3 and the output of a power source 10 for an objective lens 5 are used as the input to a computing circuit 13, and a control signal is supplied to the lens power source 12 by reading out from the prestored data the excitation degree of the lens 4 which is needed for sample-irradiating electron rays to be imaged as a spot upon an objective diaphragm 7. As a result, although the brightness of a microscopic image projected upon a fluorescent plate changes, the amplitude contrast pertinent to a lowly multiplied image can be set to the optimum state. Consequently, a clear picture photographing is enabled. |
