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73
n. b.:
The aperture diaphragm in the illumination
light path is not for adjusting image intensity.
Only use the brightness adjustment knob or
neutral density filters for this.
An aperture diaphragm in the objective is nor-
mally opened fully. Narrowing it reduces the
intensity and
increases field depth
reduces coverslip sensitivity
creates a darkfield impression
alters contrast
Possible errors
Wrong coverslip thickness or wrong objective.
Specimen with coverslip at the top instead of
the bottom.
Aperture diaphragm opened too far or closed.
Condenser at wrong height.
Light ring switched in by mistake.
Dirty optics.
Visual comparison of the objective and con-
denser apertures is done as follows: remove
an eyepiece from the eyepiece tube, or engage
the Bertrand lens by turning the knurled wheel
(62.11), (pos. B) and focus with the lever (62.11).
Close or open the aperture diaphragm until the
image just shows up in the pupil (= brighter
circle) of the objective. This is regarded as the
standard setting, i. e. condenser aperture =
objective aperture.
Replace the eyepiece or disengage the Bertrand
lens.
For low-contrast specimens, the aperture dia-
phragm can be narrowed further for clearer
imaging of fainter structures. In polarisation mi-
croscopy, narrowing the aperture diaphragm
usually results in stronger colours.