OPERATIONAxiolab 5 Illumination and contrast methods in transmitted light ZEISS05/2019 430037-7444-001 111The lines of this black cross remain closed when the stage is rotated. Depending on the section it may liewithin or outside the displayed objective pupil.With optically biaxial crystals, the cross resolves into two dark hyperbola branches (the so-calledisogyres) depending on stage rotation, which are surrounded by colored interference patternsdepending on the amount of birefringence and specimen thickness (suggestive of the figure "8").Inserting a lambda compensator (473704-0000-000) or a lambda/4 (473714-0000-000) or a 0-4 lambdawedge compensator (000000-1140-663) in the compensator slot with the initial state of the axial figurebeing as illustrated in Fig. 4-18 results in the following changes in color (shown schematically in the blueand yellow areas) of the axial figure, thus allowing differentiation in "optically positive" and "opticallynegative".Optically uniaxial Optically biaxialPositive Negative Positive NegativeLambda plate(white → blue→ yellow)+ = Blue– = YellowQuartz wedge(Direction of motionat insertion) Direction of movementLambda/4 plate(position of blackspots)Fig. 4-18 Determining the optical characterIn the case of less favorable sections in which the cross-hair center is optically uniaxial or the isogyres areoptically biaxial specimens outside the objective pupil, an assessment can be done as follows:• If the black isogyres are straight and they run parallel to the pupil (in relation to the cross-hairs), thespecimen is optically uniaxial.• If the black isogyres are curved lines which wander on a circular path through the pupil, thespecimen is optically biaxial.NOTEAxial figures can often be better displayed with circular polarization. In particular, the axisangle of optically biaxial specimens (quasi the distance between the isogyres) can be betterdetermined. The optical character can also be determined. the lambda compensator(6x20mm), arranged in the compensator slot, is used for this purpose.NOTETwo storage compartments for 6x20mm slides are located at the back of the conoscopystand.
