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What Is a Compound Microscope?

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Author: Erin Bjornsson

Optics is a branch of physics that studies the interactions of light with objects. Microscopes, cameras and other transparent “looking devices” use lenses to change the way we see objects. Using magnifying glasses and card stock, you can build a simple compound microscope. So what is a compound microscope, anyway? It's any microscope with more than one lens.

Objective: Build a simplified model of a compound microscope.

Materials

  • Newspaper (the front page would work best)
  • Tape
  • 2 large magnifying glasses
  • Cardstock
  • Scissors
  • Double-sided tape (optional)

Procedure

  1. Tape the sheet of newspaper to a wall. It is best if it has large, visible text, like the headline on a front page.
  2. Close one eye and hold up a magnifying lens in front of your open eye.
  3. Stand about 1 meter away from the newspaper.
  4. Bring the second magnifying glass between the first lens and the newspaper. Move the second lens back and forth until you can clearly see and read the newspaper text.
  5. Record your observations. Is there a certain distance at which you can read the paper through both lenses?

Building the Microscope:

  1. Make a hole for the handle and tape a piece of cardstock around one of the lenses so that it is mounted at the top of a downward facing tube.
  2. If you want, you can use double-sided tape around the edge of the magnifying glass to mount it securely in the top of the tube.
  3. Use scissors to cut a slit for your second magnifying glass, which will act as the movable lens.
  4. Insert the second lens into the tube by carefully inserting the lens through the slit and rotating it to face the correct direction.
  5. Place a small sample at the bottom of the tube and adjust the moveable lens to bring it into focus.

Results

For your first experiment, the distance at which you will be able to read the newspaper clearly will depend on the focal length of your magnifying glasses, but at some point you should be able to see very large text clearly. However, the text will appear upside-down and backwards!

Why?

Using two magnifying lenses to look at something often flips the image. Microscopes and telescopes use multiple lenses to magnify the image, and may also include lenses used to flip the image back to the correct orientation. The first (top) lens is called the objective lens. The second adjustable lens is called the projector lens.

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