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11. Troubleshooting
Problem
Bright field
The specimen can not be brought into focus.
Dark field
No definite DF contrast is possible.
The image is unevenly or not uniformly
illuminated.
Undesirable stray light.
Phase contrast
No phase contrast is possible.
Cause/remedy
Use the correct immersion medium.
Lay the specimen with the cover glass toward
the top.
Make sure that the cover glass thickness is
correct and that it meets the specifications on
the objective.
Be sure that a DF objective is being used.
The objective aperture setting is too high
(maximum 0.75). If necessary, reduce the
objective aperture using the iris diaphragm on
the objective.
Check the condenser centering.
The magnification is too weak.
Use a higher magnification.
Clean the specimen and neighboring lens sur-
faces (→
p. 77).
The specimen is too thick.
The cover glass is not placed planar.
Check the centering of the light rings
(→ p. 44).