How to Use a Student Compound Microscope
Your purchase of a microscope represents an educational investment. Properly used and cared for, it will provide years of uncompromising service. This article assumes a basic knowledge of the student-level compound microscope but highlights and reemphasizes key points to ensure success.
The following steps will become routine with continued use of the microscope:
- Plug your microscope into an appropriate 120-V outlet. Turn on the microscope’s power supply. The switch is usually located on the base. If your microscope lighting system is equipped with a rheostat control, adjust it to a bright but comfortable viewing level.
- Rotate the 4× objective into place, perpendicular to the microscope stage. The objective should click into the correct position. It is important always to start with the lowest-power (shortest) objective.
- Using the coarse-focus adjustment (the larger focus control), position the stage so that it is at the upper limit of its range of travel. This will bring the objective and stage close together but not allow them to touch.
- Carefully and securely place a slide on the stage, beneath the spring-loaded clips or the holder on a mechanical stage, centering the specimen over the hole in the stage.
- Adjust the disc or iris diaphragm, located just under the stage, so that the maximum aperture (the largest opening) is aligned with the opening in the stage. This aperture is generally used at the lowest magnification.
- While looking through the eyepiece and using the course-focus adjustment, slowly move the stage/specimen away from the objective until the image is clear. The 4× objective is best suited for scanning or viewing a large portion of your specimen. Before you select a higher magnification, center the section that you would like to view in greater detail.
- Rotate the 10× objective into place. While looking through the eyepiece and using the smaller, fine-focus adjustment (if available), clearly focus the enlarged image. You will notice that increasing magnification decreases the field of view, the relative observable area of the specimen.
- At this point, it may help to diminish the amount of light entering the specimen. Decreasing the aperture of the diaphragm will reduce glare and increase contrast in the image. Skilled use of the diaphragm or iris requires practice. It is important to select both the magnification and the degree of contrast that renders optimum detail in the observed specimen. Again, before increasing magnification, center the portion of the slide you wish to study in greater detail.
- Rotate the 40× objective into place and repeat the steps taken for the previous increase in magnification. The objectives of a high-quality microscope are parfocal, meaning that the gross image remains in focus while you rotate between objectives. It should be necessary to use only the fine-focus adjustment once the initial image is clearly viewed at low magnification. Never use the coarse-focus adjustment at high power. That can damage both the slide and the objective.
- The proper procedure for looking through a microscope is to keep both eyes open. This requires some practice but reduces eyestrain during long-term use. With practice, you can mentally block the eye that is not looking through the microscope.
- If you repeat these procedures until they are second nature, your familiarity with them will add greatly to your microscope experiences.
The objective lenses are the primary eyes of your microscope, and you need to treat them gently but keep them in good working order. Use only an aspirator, camel-hair brush, and optical lens wipes to clean them. For stubborn fingerprints or smudges, use a lens cleaner that is specially designed for use with optical equipment and rub gently with a lens wipe. Try to avoid ever having to remove the eyepiece or objectives from your microscope. Removing these parts invites dust and contamination into the internal optics and other components of the microscope. Keep a dust cover on your microscope whenever it is not in use.
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