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START-UP AND OPERATION
4
4.5. Bright field observation according to Koehler
4.5.1. Centering the condenser
5a
5b
5c
5d
Illustration 017: Centering the condenser.
PRESS and TURN the brightness control knob (1) to turn transmitted light ON
Turn the condenser up-down knob (2) in the direction of the blue arrow to raise the condens-
er to its upper limit.
Focus the specimen using the 10x objective.
Rotate the field diaphragm ring (3) in the direction of the red arrow so that the field dia-
phragm (4) is completely closed. Look through the eyepieces.
Adjust the condenser up-down knob to focus the image of field diaphragm.
If the condenser is out of center, you will see an image of the iris opening similar to (5a).
In order to center the iris opening in the field of view, use the two condenser centering
screws (6) at each side of the condenser holder.
Once the image is in focus and centered in the field of view (5b), open the field diaphragm
until the image is at least as large as field of view (5c-5d).
The field diaphragm restricts the diameter of the light beam entering the objective.
This prevents the incidence of disturbing light and increases the image contrast. To
support objective performance, the diameter of the field diaphragm must be adjusted
so that its image and the field of view are the same size.
• Use of a 4x objective open the field diaphragm completely
• Use of a 100x objective close the field diaphragm
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