Centration Of Spectrometer Slit Aperture; Correction Of Imaging Astigmatism - LEO 912 OMEGA Brief Manual

Centration of spectrometer slit aperture

1.9
1.10
LEO 912 OMEGA
Centration of spectrometer slit aperture
•
Switch to SPEC with button IMAGE/SPEC in the field SPECTROMETER.
– Spectrum caustic close to the center of the screen.
•
Center tip of the caustic to the index point with encoder in the field
SPECTROMETER.
•
Introduce slit aperture with the aperture drive and adjust the slit width
that the spectrum caustic is within the slit.
– The tip of the caustic should not be too close to the corresponding side of the
slit.
SPECIAL NOTE:
If elastic brightfield is used only, the slit width might be increased so that the caustic
tip is further off the slit edge.
•
Switch to IMAGE mode with button IMAGE/SPEC.

Correction of imaging astigmatism

•
Select a magnification between 125.000x and 250.000x with buttons
MAGNIFICATION ∆ ∇.
•
Adjust brightness by changing the emission current with encoder
CURRENT or the illumination aperture angle with the buttons
ILL APERTURE ∆ ∇.
Note, the illumination angle should not be larger than 1.6 mrad. Larger
illumination angles decrease the image quality.
•
Through-focus specimen with encoder OBJECTIVE (Grain of a carbon film
or embedding resin).
– The image is astigmatic, if the grain of the carbon film has a privileged direction
in underfocus and is turned by 90° in overfocus.
•
Switch to STIG with button SHIFT/STIG in the field IMAGE.
•
Compensate astigmatism with the encoders X and Y in the field IMAGE.
– The astigmatism is compensated, if there is no privileged direction of the grain
in under- and overfocus.
•
Switch back to SHIFT with button SHIFT/STIG in the field IMAGE.
•
Adjust brightness and magnification to the desired values.
Microscope Operation
9