OPERATIONAxiolab 5 Illumination and contrast methods in transmitted light ZEISS05/2019 430037-7444-001 1094.2.6 Configuring transmitted light polarization for conoscopic observation – determiningthe optical character of crystalsFor the classification (and thus identification) of crystalline material, the analysis of an interference imagein the objective pupil provides more valuable information than the examination of the specimen itself.This image is visible in the eyepiece when an additional lens (known as a Bertrand lens) is switched on.Alternatively, the auxiliary microscope or a diopter may be used to view the interference image.In contrast to orthoscopy, this is referred to as conoscopy, because the illumination is ideally provided bya wide open cone. In practice this means that the aperture diaphragm is fully open and the objectiveshould likewise have a large aperture.4.2.6.1 ApplicationCrystal analysis is used to determine the optical character of transparent and weakly absorbent crystals.This method is also referred to as conoscopy.Its main application is classic mineral microscopy. However, synthetic crystals, industrial minerals andplastics (e.g. films) can also be identified and characterized.(1) InstrumentationConoscopic viewing is preferably carried out on the Axiolab 5 microscope for transmitted lightconoscopy.− Strain-free objectives; recommended:N-Achroplan 50x/0.8 Pol objective orEC Plan-Neofluar 40x/0.9 Pol objective− Pol rotary stage− Polarizer D (rotatable or fixed)− 0.9 Pol condenser(2) Configuring the microscope for conoscopyIn the case of uniaxial crystals, the most favorable orientation for conoscopic viewing is obtained withthose specimen features (e.g. of a thin section) that in orthoscopic viewing change the brightness as littleas possible. In this case, the direction of viewing and the optical axis are parallel. The same applies tobiaxial crystals if viewed in or approximately in the direction of one of the two optical axes.
