ELECTROSTATIC ELECTRON-OPTICS 31 



The following equations hold for any lens : 



V2z;2 V2fi _ 1 



di — oi2. di — ai F ^ 



^^2v2 V2yi _ 1 

 ~D^ ~~D^ ~ F' 



F2 



F 



2 _ _ I2V2 



1 ~ V 2v, ' 





M - l^ - - l^£i 

 ^^^ ~ F,Dr ~ y 2v, D, * 



where M is magnification. 



