How to Calibrate the Astigmatism of Condenser Lens?

How to Calibrate the Astigmatism of the Condenser Lens?

1. At magnification = 100 kX.

2. Reduce the size of the electron beam with the "Brightness" knob so that it is almost the same as the size of a small viewing screen (reference for a rounded beam).

3. Center the electron spot on the small viewing screen with "SHIFT X" and "SHIFT Y" on the left and right panel, respectively.

4. Activate “COND STIG” and optimize the shape of the electron beam with "DEF X" and "DEF Y" (turn one knob at once):
   Focus --> DEF X or Y --> Focus --> DEF X or Y (iteratively).

5. After the electron beam shape is circular, deactivate “COND STIG”.

• Condenser astigmatism: Electron beam is not rounded, we are correcting the filament (“filament” image, i.e., the cross-over).

• Objective astigmatism: Image is stretching in one direction.