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7
Instruction
View in eyepiece
4. Center the diaphragm in
the field of view by rotating
the condenser adjusting
screws. In other words, you
adjust the illuminating path
so that it is properly aligned
along the optical axis of the
microscope.
5. Open the luminous-field
diaphragm by turning the
adjustment wheel counter-
clockwise until the edges just
disappear from the field of
view. This step ensures that
you only illuminate the field-
of-view.
6. Pull out one ocular and
look through the eyepiece
tube. Close the aperture
diaphragm by turning the
wheel in the condenser until
the aperture is about 80% of
the diameter of the objective
pupil. Replace the eyepiece.
Another way of adjusting the
aperture is by looking at your
specimen and closing the
diaphragm until resolution
and contrast are optimal.
Diaphragm too open: poor
contrast. Diaphragm too
closed: poor resolution.
When adjusting Koehler illumination for higher magnification objectives, repeat the
procedure. For lower magnifications (5x and 2.5x), the condenser performance is
changed by the removal of the swing-out lens from the light pathway, and the
condenser aperture diaphragm no longer controls the numerical aperture. Fully open
the aperture diaphrgam and control the contrast by opening/closing the field
diaphragm.