| 摘要 |
PURPOSE:To prevent a drift of an image on the surface of a material varying cyclically in a fine adjustment such as optical axis alignment by automatic cyclic change of focal distance in the lens system. CONSTITUTION:The adjustment of an object lens 7, an eccentric lens 10 and electron beam generation systems 1-3 has been completed. An axis alignment is made by roughly adjusting the position of a condenser lens 5 and exciting current is supplied 8 to the object lens 7 to form an electron beam image, which is observed on a CRT14. Then, a cyclically exciting current overlaps the object lens by a circuit 9. Deviation, if any, in the axis of the lens 5 causes a cyclical change in the alignment of the image on the CRT14 with the focal point producing a blur and a cyclical drift vertically and horizontally. A fine axis alignment to minimize the drift is made by moving the position of the lens 5 and then, the exciting current of the object lens 7 is reduced to zero to form an image by a power source 8. Thus, the required time can be reduced for the fine adjustment of the optical axis. |
