OPERATIONAxiolab 5 Illumination and contrast methods in transmitted light ZEISS05/2019 430037-7444-001 85NOTESince the apertures of objectives with an integrated aperture iris stop are too high fortransmitted light darkfield microscopy, the aperture iris stop must at least be closed to thelimit aperture of 0.65.The performance criterion for the darkfield method is always the darkest possible background of the fieldof view.• Reinsert the eyepiece into the tube.• If the height of the darkfield condenser is set correctly and sensitively, it is possible to reduce anybrightening in the field of view left, and the luminous-field diaphragm image appears almost perfectlyin focus.• Finally, match the size of the luminous-field diaphragm to the size of the field of view.Darkfield microscopy requires specimens to be considerably cleaner than in other techniques. Inparticular, fingerprints, dirt or dust particles have a negative effect, as they brighten the background ofthe field of view and decrease the contrast of the object image.(4) Setting darkfield contrast with a dry darkfield condenser• If necessary, swivel out the low-power system, polarizer or λ plate.• Move the condenser carrier down until the end stop.• Place the dry darkfield condenser in the condenser holder Z (see section 3.1.9).• Place the condenser holder Z in the condenser carrier and center it roughly, so the condenser fits intothe opening of the mechanical stage without contact when moving upwards.• Move the condenser up to the end stop. Position the specimen and adjust the illumination intensity sothat it is bright enough.• Swivel in a low-magnification objective (e.g. 5x or 10x) and focus on the specimen, using the focusingdrive.• Position a specimen so that its details are distributed evenly in the field of view. This will make theimage of the field diaphragm easier to identify.• Close the field diaphragm down to the end stop.• Lower the condenser until the edge of the field diaphragm appears sharp (luminous-field diaphragmfocus level). There will be an increasing or decreasing light ring visible when the focus is movedupwards or downwards from the field diaphragm focus level (so-called circular "breathing" of thefield diaphragm depiction).• Center the field diaphragm image with both centering screws on the condenser carrier.• Swivel in the desired objective.• Focus the specimen with the focusing drive, if necessary.• Focus the field diaphragm using the condenser drive. Open the field diaphragm enough to make theedge of the diaphragm disappear from the field of view.• Optimize the contrast with the aperture diaphragm of the condenser, if necessary.
