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How to adjust the microscope condenser?

Many users of optical microscopes often neglect some detailed problems like how to adjust the condenser. We know that the condenser is an essential component of the optical microscope illuminator.  But often the neglect of adjusting the condenser leads to the glare or gray effect because of the affection of flare veiling glare in the vision.
Below is the illustration of how to adjust the condenser.

1.Condenser Centering adjustment

  • A. Adjust and get a clear polygon:
  • Adjust the field diaphragm and the aperture diaphragm to the minimum size. We can see a clear polygon in the field if the microscope is under the correct condition. It means that the condenser is on an incorrect position if there is no clear polygon. Then please adjust the Knob (see 5.2) up and down to make the condenser move up and down slowly to get the clear polygon in the field.
    Attention: Don’t adjust the height of the condenser too often as the height has been set in the right position when the microscope is being installed. Sometimes if the polygon is not found, you can enlarge the field diaphragm to some degree and get it in a brighter condition.

  • B. Adjust the polygon to the center
  • The right position of the polygon should be in the true center. If it is not in the center, it means that the optical path is not straight. Then please adjust the Centering Screw (see 5.5), two silver knobs, to make the polygon in the center. The field which will be seen during the adjusting process is as below:



  • C. Adjust the polygon to exterior contact
  • Enlarge the field diaphragm slowly and get the optimum working position while the polygon just exterior contacts the field. Like this way the optical axis of the condenser has been adjusted to pseudaxis with the optical axis of the illumination optical path and the imaging path. Please don’t adjust the Centering Screw in the daily use when there is no need.

    2.Adjustment of the Aperture Diaphragm

    There is engraved numbers and alignment marks on the external edge of the condenser of the research microscopes. It offers convenience for adjusting the numerical aperture of the condenser to match objective’s.  But sometimes there is no engraved numbers on the external edge of the condenser. Then you have to focus the objective first and then take down one eyepiece. You can see a bright circle on the objective’s rear lens when you look into the lens cone. It has been opened too wide if a wire-frame image of aperture diaphragm not be seen. Conversely, it is too narrow while a tiny bright wire-frame image appears. The numerical aperture of the condenser matches the one of the objective when a bright circle appears.
    显微镜 聚光镜

    The main functions of the aperture diaphragm

  • Adjust the condenser’s numerical aperture to match the numerical aperture of the objective and achieve the optimum resolution. There is a close relationship between numerical aperture and resolution, so it requires the numerical aperture of them to match each other. For example, a low numerical aperture objective has to match a low numerical aperture condenser, and high matches high. Only like this the image resolution can be improved.
  • B. The aperture diaphragm infects the image’s contrast
  • 聚光镜
    The numerical aperture of the aperture diaphragm = the numerical aperture of the objective * 60% - 80%
    The left picture: the aperture diaphragm is wide, the field is bright, much vagabond ray and glare, and the contrast is bad.
    The middle picture: the aperture diaphragm is suitable, the resolution and contrast is appropriate, and the image is clear, the contrast is good.
    The right picture: The aperture diaphragm is narrow, the field is dark, the imaging detail is not clear.
    After sharing these adjusting methods, we hope that the microscope users will pay attention to the details and adjust the microscope to the optimal condition.


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