67
7. Start-up
not, recenter the image with the centering
screws. Adjust the height of the condenser
until the edges are sharp. Now open the field
diaphragm until the image fills the entire field
of view and the black edges have disappeared
completely (91.d).
• The last step is the
adaptation of the contrast
settings
. To improve the contrast, close the
aperture diaphragm – if you close it too far,
however, the resolution of the image details
will deteriorate.
To see the aperture diaphragm, remove an
eyepiece tube and look directly into the tube.
Your eye should be around 10 to 20 cm from
the tube. Change the size of the aperture
diaphragm until its image is clearly visible in
the pupil of the objective.
• Set the aperture diaphragm to cover 2/3 to 4/5
of the pupil diameter. You will now have the
optimal balance between resolution and
contrast.
a
b
c
d
Fig. 91
Koehler Illumination
a
Field diaphragm not focused, not centered
b
Field diaphragm focused, but not centered
c
Field diaphragm focused and centered
Diameter is too small, however
d
Illumination field diameter = visible field diameter
(Koehler illumination)
Fig. 90
Condenser centering
1
Centering openings
2
Height adjuster
3
Prism and phase ring centering
2
1
3
2
1
3
