OPERATIONAxiolab 5 Illumination and contrast methods in transmitted light ZEISS05/2019 430037-7444-001 105(4) ConclusionsThe gray-white color appearing first in the brightposition in the above example (Fig. 4-14/1)corresponds to a path difference of 150 nmaccording to the Michel-Lévy color chart(Fig. 4-15).When the lambda compensator is brought into thebeam path, the non-birefringent "surroundings"of the synthetic fiber appear dark red, whichcorresponds to the path difference of thecompensator of 550 nm (1st order interferencecolor for the path difference of 550 nmcorresponds to 1 λ).If the polarization direction (nγ or nγ' ) of thebirefringent sample to be examined is parallel tothe principal polarization direction (nγ) of thelambda compensator, i.e. in the NE-SW direction,the path difference of the sample (e.g. gray-white:150 nm) and the path difference of the lambdacompensator (red: 550 nm) add up. This results ina color change of the sample from grayish white togreenish-blue (resulting path difference = 700 nm).If the polarization direction of the birefringencesample to be examined is perpendicular to the principal polarization direction of the lambdacompensator, i.e. in the NW-SE direction, the path difference of the sample (e.g. gray-white: 150 nm) issubtracted from the path difference of the compensator (red: 550 nm). In this case, the interference colorof the sample visibly changes from gray-white to orange (resulting path difference = 400 nm).NOTEThe Michel-Lévy color charts are available in the literature catalog no. 42-312.4.2.5.4 Measuring path differences with the Axiolab for conoscopyThe measurement compensators are required for exact measurement. These return, i.e. compensate, thepath difference created by the specimen to zero (black of the first order).Whereas in the above-described methods the addition or subtraction position was of interest, only thesubtraction position is of interest in the measurement.Path differences in the specimen can assume very small values (1/50 λ or 10 nm) and very large values(more than 10 λ or approx. 5500 nm and more) and thus determine the compensator appropriate for themeasurement.Fig. 4-15 Schematic diagram of the colorcharts according to Michel-Lévy
