51
Preparation errors
Possible sources of error if ICT image
quality is
unsatisfactory:
Embedding medium, specimen slide (petri dish)
or object (e.g. crystals, fibres) are of birefringent
material. The phase shifts caused by
birefringence disturb the interference contrast
image. This can sometimes be remedied by
rotating the specimen.
The specimen is too thick or too thin.
The specimen slide or coverglass is too thick.
The difference in the refractive indices of the
specimen and the embedding medium is too
small (this often happens when uncovered
specimens are observed with an immersion
objective).
Inhomogeneous mounting medium.
Objects with parallel structure: object is at a
wrong azimuthal orientation (remedy: rotate
object with stage (34.7)).
Errors in instrumentation
Polarizers not engaged, or rotated too far out of
the crossed position, or, though crossed, turned
out of the zero position.
Polarizer has been damaged by powerful light
sources. Check this by holding the polarizer
against a window or light source. Damaged light
sources then show distinctly uneven colouring.
The IC prisms in the condenser are in the wrong
position or upside down (
→
p. 15) or decentred
(Fig. 36). This is checked by combining an IC
prism with all available objectives and seeing if
the interference contrast image is optimal at
corresponding magnifications of the objective
and the condenser.
The condenser top is not engaged or the wrong
condenser top is being used (only 0.90 S1, 0.90
S1 or P 1.40 OIL, see optics data sheet).
Koehler illumination not set (image of field
diaphragm in the specimen plane).
Aperture diaphragm too wide or too narrow.
Dirty optics or polarizer.
Dust protection
Turn the condenser prism out of the light path if
it is not being used for a long time, keep
objective prisms in a dust-free place. Clean
condenser front lens frequently.
Summary of Contents for DM L
Page 1: ...Leica DM L Instructions...
