Steps to adjust the C2 aperture mechanical position are:
Make sure the C2 aperture is in.
At around 5kX, cross the beam first and center beam using deflectors (), then spread the beam until its diameter is close to 5cm ring on the screen. Adjust screws X & Y on C2 aperture to center the beam. Repeat this process 2-3 times.
At high mag ~30kX or higher, change the of beam(C2) through the crossover and adjust the screws X,Y to make the beam symmetric when spreading out.
There are two ways to check and adjust the C2 stigmatism:
When the filament is desaturated, press button and select , then adjust so that the details in the filament shadowing image can be clearest and sharpest.
When changing the beam intensity, use the to adjust the beam into symmetric and "round" shape, i.e. not elliptical.
For this purpose, don't pay attention to the beam shape when beam is exactly at cross point, as that more reflects the shape of the crystal tip, rather than stigmatism. You want to make beam "round" when spreat out.
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