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13. Bertrand Lens
The Bertrand lens is built into the microscope and enables the user to switch quickly
between orthoscopic (Bertrand lens out) and conoscopic (Bertrand lens in).
14. Use of Compensators
The slot in the body of the microscope between the nosepiece and the viewing head of the
o
microscope, set at 45
to the N-S axis is for the insertion of the supplied compensators.
These should be inserted when the colour of the specimen is at its maximum, that is, when it
o
is turned 45
from the position of extinction. Compensators provided for use with the
PriorLux POL are DIN standard.
Quartz Wedge
When a wedge of uniaxial crystal of quartz, cut parallel to the optic axis is inserted into the
compensator slot between crossed polars a series of interference colours will be observed.
The retardation caused by the specimen can be assessed by its compensation of an order of
colour of the wedge. The Prior quartz wedges are mounted length "fast" and when the
interference colour of a mineral specimen is compensated by placing the slow of the wedge
on the fast of the specimen, the position of the colour in Newton's scale can be ascertained.
The quartz wedge is wedge is used when the birefringence specimen and the interference
colours are high.
Sensitive Tint Plate
The type of compensator is often also referred to as a first order red compensator. It is cut
to give an interference colour at a very sensitive part of the colour scale. When inserted
between crossed polars the fast and slow direction of a birefringent material can be
determined. The specimen is rotated until the colour order is raised or lowered by the
maximum amount. If the colour raised, the fast direction is coincident with the fast direction
of the sensitive tint plate.
P r i o r L u x P O L
™
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