B 40 - 017 e / 12.96
4 Instructions for use
4.3 Application examples
4.3.1 Orthoscopic work in linearly polarized light
Example 1: Measuring the angle 2 V of the optical
axis of a biaxial crystal
Center the selected grain in the crosslines.
Switch in the 5x/0.13 objective (standard use).
Adjust the iris diaphragms of the 20x/0.30 and
50x/0.60 objectives and the aperture dia-
phragm of the condenser (Fig. 3/
12
) to in-
crease the contrast of the
Axiolab Pol
(same
procedure for
Axioplan
-microscopes).
Rotate through the A
1
axis to dark position.
Tilt about A
4
axis (max. possible angle). Nor-
mally this will result in brightening up.
Tilt about the A
2
axis to dark position.
Tilt about the A
4
axis in opposite direction until it
brightens up.
Rotate through the A
1
axis to extinction.
If the grain remains dark when the stage is tilted
about the A
4
axis, the plane of the optical axis
lies parallel to the microscope's symmetry
plane (if not, repeat the previously described
steps).
Clamp the A
2
axis (Fig. 3/
21
).
For
Axioplan
microscopes, release the clamp-
ing device of the microscope stage (Fig. 4/
5
)
and rotate the universal rotary stage by 45°
through the A
5
axis up to the next click stop.
Use the graduated circle and the vernier
(Fig. 3/
19
). to measure the optical axes (dark
position when tilted about the A
4
axis).
If only one of the axes of a biaxial crystal lies
between the tilting range A
4
, the angle of the
optical axes must be determined using the
Wulff network (Fig. 5).
4.3.2 Conoscopic work in linearly polarized light
The advantage of the conoscopic over the ortho-
scopic method is that the axial directions of
monaxial or biaxial crystals can be identified di-
rectly in the interference image. For this purpose, a
high-aperture (e.g. 50x/0.60) LD (long distance)
objective and a Bertrand lens permitting observa-
tion of the rear focal plane of the objective are
required.
Example 2:Measuring the angle 2 V of the optical
axis of a biaxial crystal
(conoscopically)
Proceed as described in
example 1
(steps 1 to
10).
Switch in the 50x/0.60 objective.
Switch in the Bertrand lens (focus
Axioplan
mi-
croscopes).
Use the graduated circle and the vernier
(Fig. 3/
19
) to measure the optical axis by tilting
about A
4.
The axial directions can be identified
from the curved, dark , hyperbola branches.
The exit point of the crystal's optical axis lies in
the vertex of the hyperbola.
Note:
If only one optical axis is located within
the tilting range about A
4
, proceed as
described in
example 1
.
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