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Köhler Illumination: Interactive Tutorials

Condenser Alignment
Field Diaphragm Opening Size

This tutorial demonstrates how the condenser is centered in the optical path and the size of the field diaphragm opening is determined when adjusting a microscope for proper Köhler illumination. Operating instructions appear just below the tutorial window.

The default initial state of the microscope is severely out of alignment. To operate this tutorial, use the sliders to shift the focus of the sample image and to position both the condenser and the field diaphragm according to the steps below:

  • Use the "Specimen Fine Focus" slider to focus the specimen. This is similar to adjusting the coarse and fine focus on the microscope.
  • Adjust the "Diaphragm Opening Size" slider to close the field diaphragm to its narrowest opening size. On a real microscope, this is usually done using a knurled wheel or lever at the base of the microscope.
  • The "Condenser Height" slider simulates raising and lowering of the condenser on its substage-mounted rack. Use this slider to "focus" the leaves of the field diaphragm. When comparing this part of the tutorial to a real microscope, consider that this action mimics hand-rotation of the substage condenser elevating knob that moves the condenser up and down with respect to the microscope stage.
  • Slide the X and Y Translation sliders until the closed field diaphragm image is centered in the viewfield.
  • Alternatively, use the mouse cursor and the left-hand mouse button to move the white circle inside of the "Condenser Alignment" box. This allows for simultaneous translation in both the X and Y directions.
  • After the image of the field diaphragm is centered and focused, use the "Diaphragm Opening Size" slider to increase the size of the field diaphragm opening until it just clears the yellow hatch marks in the viewfield. This is the optimum adjustment for photomicrography.
  • Use the "Reset" button to randomly change the default alignment parameters so that students can practice over and over again until they have a comfortable "feel" for condenser and field diaphragm alignment.

Contributing Authors

Mortimer Abramowitz - Olympus America, Inc., Two Corporate Center Drive., Melville, New York, 11747.

Matthew J. Parry-Hill and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.


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