5 OPERATION
5-32
EM210F-1
5.3.6 Objective Lens Astigmatism Correction
Fig. 5.31
5.3.6a
At Middle Magnifications
A perforated, thin plastic film reinforced with carbon is recommended as a test specimen
for astigmatism correction.
1.
Select “Maintenance” on the “TEN Controller” main menu to display the
“Alignment Panel for Maintenance” screen.
2.
Set the magnification to 20,000 times in the MAG mode.
3.
Use BRIGHTNESS (L1-
⑦
) to adjust the image brightness and SHIFT (L1-
⑧
,
R1-
③
) to adjust the beam position.
4.
Focus the image using OBJ FOCUS (R1-
⑥
).
5.
Use the trackball (SC-
②
) or X,Y buttons (SC-
①
) to bring a suitable hole on
the specimen to the screen center.
6.
Press OBJ STIG (L1-
⑥
) or “DEF Selector-OL” on the “Alignment Panel for
Maintenance” screen.
7.
Manipulate OBJ FOCUS (R1-
⑥
) so that the a fresnel fringe (A white line
seen along the hole edge when slightly over-focused) appears along the
edge of the hole.
?
The distance between the line and hole edge (
F
“d” in Fig. 5.32a) is uneven
when astigmatism exists in the objective lens.
8.
Manipulate DEF/STIG (L1-
⑩
, R1-
④
) so that the image contrast and distance
between the line and hole edge (
F
“d” on the figure shown below) be-
comes even in all directions.
?
If the objective aperture or the specimen is dirty, or the objective aperture is not
correctly inserted in the beam path, or the voltage center is not properly set, it
may be impossible to correct astigmatism completely.
