5 - 20
NOTE
: The brightness of the image can vary to some extent from adjustment guidelines
due to the particular combination of a filament and an Wehnelt.
If the image is dark, reduce the number of spacers supplied with the cartridge
filament one by one. Conversely, if the image is too bright, increase the number of
spacers one by one. Two adjustment spacers are provided on the lid of the
cartridge filament. Using fewer spacers could reduce the life length of the filament.
A dirty objective aperture or condenser lens aperture can cause an increase of
astigmatism, and so the image similar to that shown in Figure 5.2-18 can not be
acquired. In such a case, replace the condenser lens aperture (see 5.3) and the
objective aperture (see 5.4).
