Zeiss Axiolab A Bedienerhandbuch PDF herunterladen (Seite 53)

Axiolab A Carl Zeiss

B 40-015 e 06/99 3-11

Uniaxial Crystals

If the optical axis of a uniaxial crystal is oriented parallel to the observation direction, a dark cross which

can be surrounded by concentric interference rings (depending on birefringence and specimen thickness)

becomes visible in the conoscopic observation mode. These interference rings are also called isochromats

(from the Greek isos = equal and chroma = color).

The cross is maintained when the stage is turned. Observe the NE quadrant of the cross (1

quadrant;

counting is made counterclockwise).

If you use the λ-compensator:

• After insertion of the λ-compensator, the following appears in the first and third quadrant near the

center of the dark cross:

− yellow = optically negative

− blue = optically positive

Biaxial Crystals

If biaxial crystals show a cross in conoscopic observation which is resolved into two hyperbola legs when

the stage is turned, the acute bisectrix (1

center line) is oriented parallel to the observation direction.

Turn the stage until the dark hyperbola legs (isogyres) are in the first and third quadrant.

If you use the λ-compensator:

• The following appears after insertion of the λ-compensator:

− yellow = optically negative

− blue = optically positive

Fig. 3-8 Determine the optical character of crystals

☞

If one optical axis of a biaxial crystal is oriented parallel to the observation direction, only one

hyperbola leg is visible in conoscopic observation, the vertex of which lies in the center of the

field of view. When the stages are turned, the hyperbola leg moves around its vertex. The

determination of the optical character is performed in the same way.

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Zeiss Axiolab A Bedienerhandbuch Seite 53