Steps and Methods for Calibrating a Metallographic Microscope

1. Adjust the position of the microscope and the light source so that the light source is aligned with the microscope’s flat condenser mirror, but at a distance of at least 10 inches.
2. Adjust the light so that the filament is clearly focused on the flat condenser mirror.
3. Adjust the mirror so that the light is transmitted from the center of the condenser mirror to the condenser located beneath the stage.
4. Place a slide on the stage, lower the condenser, and align it with the slide specimen. Focus sequentially from low magnification to high magnification.
5. Focus clearly on the slide specimen. You may need to raise the condenser slightly to obtain sufficient illumination.
6. Set the aperture on the light source to its smallest setting. Carefully rotate the condenser assembly beneath the stage up (or down) until this reduced aperture is focused on the same plane as the slide. Do not focus the microscope itself at this stage (i.e., do not adjust the knobs above the stage).
7. If your microscope has a condenser adjustment function, use it to move the image of the reduced aperture to the exact center of the field of view (most research microscopes you will use require this step to position the aperture at the center of the field of view).
8. Open the aperture ring until the polygonal aperture ring just fills the field of view.
9. If possible, remove one eyepiece. Reduce the aperture of the condenser’s iris diaphragm beneath the stage and look into the tube to observe the objective lens. The light should appear symmetrical at this point. In research microscopes, any asymmetry can be adjusted at this stage.
10. Open or close the iris diaphragm on the condenser under the stage so that only 23% of the objective’s field of view is illuminated. Replace the eyepiece. At this point, system alignment is complete, and the microscope is ready for slide examination. 11. When using low-power, medium-power, and oil immersion objectives, some compromise is necessary. On the microscope you are using, this compromise involves adjusting the height of the condenser. You must adjust the light intensity by moving the condenser to a position lower than the correct height.
Consider what you are sacrificing when making this adjustment.
Never control light intensity by moving the condenser, adjusting the iris diaphragm on the condenser beneath the stage, or by increasing or decreasing the light source. The ideal method is to use a neutral filter (i.e., a gray filter).