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5.7 Adjustment of Köhler illumination for transmitted light
In order to obtain perfect image results during microscopic observation, it is important
that the light guidance of the microscope is optimized. If illumination can be adjusted
according to Köhler, this results in homogeneous illumination of the specimen and the
reduction of disturbing stray light.
Necessary control elements for this are:
•
Height adjustable and centerable condenser with aperture diaphragm
•
Illuminated field diaphragm
For the first adjustment of Köhler's illumination, the smallest possible objective
magnification must first be selected so that the following steps can then be carried out.
1. Move the condenser with the condenser focus wheel to a
position directly under the specimen stage. Switch on the
illumination and focus the specimen, which is placed with
the cover glass facing upwards, using the coarse and fine
adjustment knobs.
2. Close the field diaphragm completely at its adjustment ring.
When looking into the microscope, a blurred image of the
aperture appears. If the microscopic image becomes
completely dark, the image of the field diaphragm is
outside the field of view and must be brought into the field
of view by the centering screws of the condenser.
