Alignment

In order to optimize the performance of the compound light microscope it is necessary to have the instrument in proper alignment. The standard procedure for such alignment is often called Köehler illumination. The basic steps are as follows:

1. If using a mirror or external light source, adjust them so as to direct the light onto the center of the condenser lens.

2. Focus the microscope at low magnification on a specimen slide, and adjust the condenser up or down until the edge of the partially closed diaphragm of the light source is in focus with the object.

3. Center the condenser (if necessary) by adjusting the condenser diaphragm.

4. Adjust the lateral positioning and opening of the illuminating diaphragm so that it is concentric with the field of view and only just fills it fully.

5. Remove an eyepiece and examine the back of the objective lens.

6. Stop down the condenser diaphragm until only 2/3 of the diameter of the image area is illuminated.

7. Use neutral-density filters to cut down on illumination, if necessary.

If black and white photographic film is used for micrography, plan to employ a green filter. The monochromatic green light will not be subject to chromatic aberration which reduces resolution.

If you wear glasses, they can normally be removed when working with the light microscope, thus avoiding the possibility of scratches on them from contact with the microscope eyepiece assembly. Exceptions occur in the case of individuals who have significant problems with astigmatism or glaucoma. These individuals may need to use their glasses and should use rubber pads on the eyepiece assembly to cushion impact with the glasses.