OPERATION
Axioscope 5/7/Vario
Illumination and contrast methods in transmitted light …
ZEISS
03/2018
430035-7344-001
91
NOTE
Objectives with built-in iris apertures have apertures which are too high for the transmitted
light darkfield microscopy. Stop the iris aperture down at least until it reaches the border
aperture for the darkfield of the condenser in use.
Performance criterion for the darkfield method is always the darkest possible background for the field of
view.
•
Replace the eyepiece in the tube.
•
Lighter areas which might still be visible in the field of view are reduced when the darkfield condenser
is adjusted correctly and delicately. You now have an approximately sharp eye diaphragm image.
•
Now adjust the field diaphragm diameter to the size of the field of view.
Darkfield samples need to be kept impeccably clean, more so than samples for any other method. A
fingerprint, dust or any dirt particle can have a negative effect, as they brighten the background and
reduce the contrast of the object image.
(4) Setting darkfield contrast with a dry darkfield condenser
•
If necessary, swivel out the low-power system, polarizer or
λ
plate.
•
Move the condenser carrier down until the end stop.
•
Place the dry darkfield condenser in the condenser holder Z (see section 3.1.14).
•
Place the condenser holder Z in the condenser carrier and center it roughly, so the condenser fits into
the opening of the mechanical stage without contact, when moving upwards.
•
Move the condenser up until the end stop. Place the specimen and adjust the illumination intensity to
bright enough.
•
Swivel in an objective with small magnification (e.g. 5x or 10x) and focus the specimen, using the
focusing drive.
•
Place a specimen as its details are distributed evenly in the field of view. This will make the image of
the field diaphragm easier to identify.
•
Close the field diaphragm until the end stop.
•
Lower condenser until edge of field diaphragm appears sharp (luminous-field diaphragm focus level).
There will be an increasing or decreasing light ring visible, when moving the focus upwards or
downwards from the field diaphragm focus level (so called circular "breathing" of the field diaphragm
depiction).
•
Center the field diaphragm image with both centering screws on the condenser carrier.
•
Swivel in the desired objective.
•
Focus the specimen with the focusing drive, if necessary.
•
Focus the field diaphragm, using the condenser drive. Open the field diaphragm enough to make the
edge of the diaphragm disappear from the field of view.
•
Optimize the contrast with the condenser, if necessary.
