ELECTRON MICKOSCOPY 



O 0'2 0-4 0-6 0-8 I-O 1-2 1-4 1-6 IB 



Fig. 7. The focal properties of an electrostatic lens as a function of its geometry. 



90 



80 



70 



Cs/S 



60! 



SO 



40- 



30 



20- 



lO 



1-2 



1-4 



O 02 0-4 0-6 0-8 I-O 



Fig. 8. The spherical aberration of an electrostatic lens as a function of its geometry. 



154 



