METHOD AND APPARATUS FOR CONTROLLING THE OBJECTIVE LENS IN A SCANNING ELECTRON MICROSCOPE ON THE LIKE

摘要

The relation between the focusing distance of the objective lens and the excitation current of the objective lens is stored in a data memory. The initial focusing distance corresponding to the optimum excitation current is determined as a result of the focusing adjustment operation. Then the change in the focusing distance due to the specimen shift along the optical axis of the object lens is detected. The magnitude of the excitation current corresponding to the focusing distance is read from the memory and a current of that magnitude is supplied to the object lens.