Friday, May 17, 2013

Adjusting Condensers

The condenser aperture diaphragm is used to control the contrast and resolution of an image. An improper setting of the condenser aperture diaphragm  can be the cause of much frustration both for teachers and students. Students may attempt to find the focus with the condenser aperture diaphragm all the way open.

Remember, an open condenser aperture diaphragm results in a low depth of field. Students may not see anything at all when working with high magnifications because the image is too dark. In this case the diaphragm is closed too much. The diaphragm should not be used to control the amount of light, but for some specimens or magnifications there may simply be no way around this especially if the lamp is not very powerful. The higher the magnification, the more need for a condenser.


  • Completely close the condenser aperture diaphragm when starting to use the microscope. 
  • Rotate the low power objective into position and find the focus with the coarse focus knob. The larger depth of field and higher contrast makes it easier for the students to focus the specimen. 
  • When switching to a higher magnification, the students should start to gradually open the condenser aperture diaphragm, to observe the differences in image quality. 
  •  Adjust the light intensity with the dimmer to prevent glare. Students should be made aware that the condenser aperture diaphragm should be adjusted to the numerical aperture value which is printed on the objective.
  • Opening the diaphragm further will not increase image quality, but may result in glare. If the sample is thick, strongly stained or pigmented then the diaphragm has to be opened to allow more light to pass through the specimen. As a consequence, the depth of field becomes smaller.
  •  Use the fine focus adjustment knob to focus through the different layers of the specimen
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