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OPERATION
Carl Zeiss
Illumination and contrast methods
Axio Imager
166
430000-7344-001
M70-2-0020 e 06/2009
•
Push the Bertrand lens slider into the light path. Focus the axial figure by means of the lever of the
slider,
or,
on the tube lens turret, swivel the position with the Bertrand lens into the light path, and focus the
axial image by turning the focusing wheel.
(5) Evaluation
Crystalline anisotropic specimens can be classified in optically uniaxial and biaxial specimens, each with
"optically positive" or "optically negative" character.
Uniaxial
crystals show a
black cross
, if the optical axis is oriented parallel to the viewing direction.
Dependent on the degree of birefringence and the specimen thickness
concentrically arranged
colored
interference fringes (the so-called isochromats)
might appear (see Fig. 4-127, second row).
This cross remains closed, when you rotate the stage. It can be located inside or outside the imaged
objective pupil, depending on the position of the section.
With
optically biaxial
crystals, the cross resolves into two
dark hyperbola branches (the so-called
isogyres)
depending on stage rotation
, which are surrounded by colored interference patterns
depending on the amount of birefringence and specimen thickness (suggestive of the figure "8").
Inserting a compensator
λ
(473704-0000-000) or
λ
/4 (473714-0000-000) or a wedge compensator 0-4
λ
(000000-1140-663) in the compensator slot with the initial state of the axial figure being as illustrated in
Fig. 4-127 results in the following changes in color shown schematically (blue and yellow areas) to the
axial figure, thus allowing differentiation in "optically positive" and "optically negative".
Optically uniaxial
Optically biaxial
Positive Negative Positive Negative
λ
plate
(white
→
blue
→
yellow)
+ = blue
– = yellow
Quartz wedge
(Direction of motion
at insertion)
Ò
Direction of
Ó
movement
λ
/4 plate
(position of black
spots)
Fig. 4-127 Determining the optical character