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71
Operation of transmitted light
Setting the aperture diaphragm
The aperture diaphragm determines the lateral
resolution, field depth and contrast of the
microscope image. The best contrast is
obtained when the apertures of the objective
and the condenser are roughly the same.
When the aperture diaphragm is stopped down
to be smaller than the objective aperture,
resolving power is reduced, but the contrast is
enhanced. A noticeable reduction in the re-
solving power is observed when the aperture
diaphragm is stopped down to less than 0.6x of
the objective aperture and should be avoided
where possible.
Brightfield illumination with condenser
0.30 S70
Brightfield illumination is possible with objective
magnifications of 2.5x to 40x.
Turn a 10x objective into the light path and focus
the specimen with the coarse and fine drive.
Narrow the aperture diaphragm until you obtain
the desired image contrast.
Brightfield illumination with condensers
0.53 S23 and 0.90 S1
Brightfield illumination is possible with condens-
er 0.53 S23 with objective magnifications from 5x
to 100x, and with condenser 0.90 S1 from 10x to
100x. A P 1.40 OIL S1 condenser top is available
for extremely high resolution.
Brightfield illumination
Illumination techniques where the empty areas
of the specimen are the brightest parts are
called brightfield. Absorbing specimen struc-
tures are required for brightfield imaging, i. e.
most specimens will need staining. Alternati-
ves are optical contrasting techniques such as
phase or modulation contrast.
Setting the condenser
On the TL illumination column there are height
markings – S70, S23 and S1 – (13.3) for setting
the correct condenser height. Using the
supplied hexagonal screwdriver, slacken the
screw (14.1) and adjust the height of the
condenser or condenser holder until its upper
edge coincides with the corresponding con-
denser height marking on the illumination
column. Retighten the condenser or condenser
holder fixing screw.