How to Focus a Microscope

Focusing a microscope properly is key to seeing all the fine detail you expect. A microscope will almost never have the right focus when you first use it to look at a specimen. That is why it is essential that you learn how to focus a microscope.

Instructions

Difficulty: Moderately Easy

Things You’ll Need:

• Slide
• Specimen

1. Place a prepared slide on the viewing tray of your microscope.
2. Look through the eyepiece of your microscope to see the specimen on your slide. The image you see will likely be fuzzy and unrecognizable.
3. Slowly turn the coarse focus knob on your microscope. This will be a large knob, usually located on the side of the microscope. Keep turning the coarse focus knob until you can recognize what you are seeing.
4. Turn the fine focus knob. This is a small knob, usually located below or beside the coarse focus knob. Keep turning until the intricate details of your specimen begin to become visible. Intricate details include things like individual hairs, the various parts of a compound eye on a bug or the mites in a particle of dust.
5. Turn the diaphragm of your microscope. This is a large disc located below the eyepiece and above the lens. The diaphragm controls how much light can go through the lens.
6. Notice a distinct contrast between your specimen and the slide. This is caused by the amount of light let through by the diaphragm.
7. Adjust the slide on the viewing tray as necessary to get a full view of the specimen. Be sure only to touch the edges of the slide when moving it around.

Tips & Warnings

• Some microscopes come with removable lenses. Others, like compound microscopes, have multiple lenses that can be rotated for different magnifications. For microscopes such as these, you will need to refocus each time you change to a different lens.
• Not every microscope comes with fine focus capabilities. However, all microscopes come with a coarse focus function. Fine focus microscopes are used for serious scientific investigations from the middle school level on up to professional researchers. Coarse focus microscopes are most commonly used by small children who are being introduced to microscopes for the first time.
• When you are changing lenses on a microscope, take care not to touch the glass part of the lens. Doing so will leave a fingerprint—and possibly dirt—behind. This will cause visual distortions when you view your next specimen.

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