Operation Of Transmitted Light - Leica DMIL Mode D'emploi

Operation of transmitted light

Bright-field illumination
Illumination methods which show object-free
areas of the specimen as the brightest parts of
the image are called bright-field. Bright-field
illumination requires absorbing object struc-
tures, i. e. staining of the specimen is useful in
most cases. Alternatives are optical contrast
methods, such as phase contrast or modulation
contrast.
Adjusting the condenser
To aid in proper level adjustment of the S 90 und
S 55 condensers, markings (46.1) are located on
the column. These markings indicate a liquid
level of 15 mm. For microscope stands with dual
markings, the lower line indicates a liquid level
of 15 mm while the upper line indicates a liquid
level of 50 mm.
• Press the catch lever (46.2) and adjust the
incident-light illumination carrier until the
upper edge of the carrier and the corres-
ponding condenser level marking match.
Adjusting the aperture diaphragm
The aperture diaphragm (46.3) determines
resolution, depth of field, and contrast of the
microscope image. The best resolution is
obtained when the apertures of the objective
and of the condenser are roughly the same.
Reducing the aperture diaphragm to be smaller
than the objective aperture will reduce the reso-
lution but enhance the contrast. A noticeable
reduction in resolution occurs when the
aperture diaphragm is reduced to less than 0.6x
of the objective aperture and should be avoided
where possible.
• Adjust the aperture diaphragm according to
your subjective impression of the image.
• You may basically achieve a calibration by
comparison with the apertures of different
objectives.
• Visual comparison between the apertures of
the objective and the condenser can be made
as follows:
• Remove the eyepiece from the eyepiece
tube or use an focusing telescope and
focus.
• Close or open the aperture diaphragm until
its image is just visible in the objective pupil
(= brighter circle). This is considered the
standard setting, i. e. condenser aperture =
objective aperture.
• Reattach the eyepiece.
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