OPERATION
ZEISS
Illumination and contrast methods in transmitted light …
Axioscope 5/7/Vario
110
430035-7344-001
03/2018
•
Swivel in the recommended objective and focus with the focusing drive.
•
Close the luminous-field diaphragm as far as necessary to prevent the axial figures of adjacent crystals
from being superimposed on the axial figure. The smallest crystal extension that can be masked out is
105 µm.
•
Push the Bertrand lens slider incorporated in the intermediate plate into its active position. When you
have done this, the axial figure appears in the field of view.
•
Focus the axial figure by rotating the lever of the Bertrand lens slider.
4.2.7.5
Evaluation
Crystalline anisotropic specimens can be classified in optically uniaxial and biaxial specimens, each with an
"optically positive" or "optically negative" character.
Uniaxial
crystals show a
black cross
if the optical axis runs parallel to the viewing direction.
Depending
on the degree of birefringence and the specimen thickness,
concentrically arranged colored
interference fringes (the so-called isochromates)
might appear (see also Fig. 4-13, second row).
The lines of this black cross remain 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").
When inserting a
λ
compensator (473704-0000-000) or
λ
/4 (473714-0000-000) or a 0-4
λ
wedge
compensator (000000-1140-663) into the compensator slot, with the initial state of the axial figure as
illustrated in Fig. 4-13, the schematically shown changes in color (blue and yellow areas) will result in the
axial figure, thus allowing the 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
movement when
inserted)
Direction of
movement
λ
/4 plate
(position of black
spots)
Fig. 4-13
Determining the optical character