Leica DM LSP, Instructions Manual

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A particularly exact way of crossing the polar-
izers is to use the built-in Bertrand lens (43.3)
or the auxiliary telescope (25.1) as follows:
Use an objective with a fairly high magnification,
e. g. 40x, 50x, 63x.
Open the aperture diaphragm (43.7) (PH position).
For the auxiliary telescope: foxus until the some-
what brighter circle in the middle of the field of
view is sharply defined.
When the polarizer is not quite adjusted, 2 dark
stripes are visible which close to form a cross
when the polarizers are exactly crossed (44a).
This cross usually does not close completely in
the case of objectives and condensers without
the P engraving.
The following section is only intended to give a
rough survey of the examination methods.
Further details can be found in textbooks on
polarization microscopy.
Examinations: One polarizer only
If specimens are to be examined with other
transmitted light methods such as brightfield,
phase contrast and darkfield instead of with
crossed polarizers, it is usually sufficient to dis-
engage either the analyser
or the polarizer. If the
image is not bright enough, both the polarizer
and the analyser should be disengaged.
Birefringent specimens with inherent colours
may exhibit changes in brightness and/or colour
when the stage or polarizer is rotated (with
analyser disengaged). This so-called dichroism
or pleochroism is a key indication in crystal
examinations. However, this effect can be simu-
lated on non-polarizing microscopes which have
no depolarizing quartz plate, or also if an inci-
dent light reflector has been left in the light path
when transmitted light is switched on.
Fig. 44 Crossing the polarizers, viewing with a Bertrand lens
and a high-aperture objective, without a specimen
a exactly crossed, b not exactly crossed
Often, Pos. a cannot be set at all if there is strain in the con-
denser or objective
Operation of transmitted light polarization
a
b
02_Mont_Anl_DMLSP eng.qxp 01.03.2001 16:47 Uhr Seite 9