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80
Fig.␣ 67␣
Setting ICT contrast
Choice of prisms
Choose the objective-side prism with the letter
indicated in the top line of the objective en-
graving, e. g. C for pupil position C, by rotating
the turret.
Choose the condenser-side prism that corre-
sponds to the magnification of the objective
used, e. g. pos. 40 for objective 40x, by rotating
the disc.
Setting ICT contrast
Turn the objective-side prism turret to the left
and right (Fig. 67). Also adjust the contrast with
the aperture diaphragm. Optimum contrast for
specimens with parallel structures can be
obtained by rotating the specimen. Colour
contrast: Turn over the analyser, so that the
lambda sign can be seen on the top.
Sources of error if ICT image quality
is unsatisfactory
Embedding medium, specimen slide (petri dish)
or specimens (e. g. crystals, fibres) are of
birefringent material. The phase shifts caused
by birefringence disturb the interference con-
trast image. This can sometimes be remedied
by rotating the specimen.