Zeiss Axiolab A Operating Manual

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Zeiss Axiolab A Operating Manual Manual pdf 53 page image

Axiolab A Carl ZeissB 40-015 e 06/99 3-11Uniaxial CrystalsIf the optical axis of a uniaxial crystal is oriented parallel to the observation direction, a dark cross whichcan 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 (1st 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 thecenter of the dark cross:− yellow = optically negative− blue = optically positiveBiaxial CrystalsIf biaxial crystals show a cross in conoscopic observation which is resolved into two hyperbola legs whenthe stage is turned, the acute bisectrix (1st 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 positiveFig. 3-8 Determine the optical character of crystals If one optical axis of a biaxial crystal is oriented parallel to the observation direction, only onehyperbola leg is visible in conoscopic observation, the vertex of which lies in the center of thefield of view. When the stages are turned, the hyperbola leg moves around its vertex. Thedetermination of the optical character is performed in the same way.