Zeiss Axio Imager 2 - Page 174

ZEISS OPERATION Axio Imager 2
Illumination and contrast methods
174 430000-7544-001 01/2016
(3) Setting the microscope
The microscope has been prepared as described in Section 4.12.5.1 (3).
• Rotate the rotary stage Pol with the specimen, e.g. a synthetic fiber, until the specimen appears as
dark as possible. In this position, the fiber extends parallel to one of the two directions of the
crosslines reticle.
• Next, turn the rotary stage Pol through a further 45° until the longitudinal axis of the fiber is oriented
NORTH-EAST (NE) – SOUTH-WEST (SW) (Fig. 200). In this position, the specimen exhibits the maximum
brightness (diagonal position) and may appear in any color.
• Push in the full-wave compensator λ.
Like the specimen, the compensator λ is a birefringent object, though one with a defined path difference
of 550 nm and a defined principal vibration direction n
γ
oriented NE-SW.
By moving the compensator λ into the light path, the specimen changes its color. The nature of the color
change depends on the orientation of the specimen (NE-SW or NW-SE).
The changes in color are due to optical interference. The interference colors (path differences) in both
diagonal positions (NE-SW and NW-SE) of the specimen must be compared.
The path difference results from the superposition (interference) of the vibration direction of the
specimen with the vibration direction of the compensator λ.
There is a greater path difference if the vibration direction of the specimen with the highest absolute or
relative refractive index (n
γ
or n
γ
') is parallel to the principal vibration direction of the compensator λ. The
specimen will then appear, for instance, greenish-blue (Fig. 200/2
).
The smallest path difference occurs if the vibration direction of the specimen with the lowest absolute or
relative refractive index (n
α
or n
α
') is perpendicular to the vibration direction of the compensator λ. The
specimen will then appear e.g. yellow (Fig. 200/3
).