How to Make a Homemade Refracting Telescope

Creating a homemade refracting telescope can be a fun and educational activity.

Telescopes are instruments that are used to magnify and focus distant objects so they can be easily seen. Telescopes can use a variety of optical principles to achieve this task. Refractive telescopes, for example, use a lens to focus light from objects to create an image which is magnified when viewed through an eyepiece. While powerful refractive telescopes can be large and expensive, it is possible to build your own homemade telescope using a few short steps.

Things You'll Need

• Ruler
• 2 convex lenses
• Small light source (e.g. flashlight, lamp)
• Telescoping tubes (one larger than the other)
• Manila paper
• X-Acto knife
• Saw or serrated knife
• Glue

Instructions

1. Use the light source to determine the focal lengths of the lens by placing the light above the lens and moving the light up and down until the the light is focused into a single bright point. Measure the distance between the light source and the lens, which is the focal length. Repeat this process for both lenses, then add the focal length of both lenses together.

2. Use the saw to cut the telescoping tubes to a length of half the combined focal length of the lenses, plus an additional inch.

3. Cut a circle out of the manila paper with the same diameter as the telescoping tube. Repeat this for both telescoping tubes.

4. With a pencil, outline a circle on the manila paper circles with a diameter slightly smaller than the diameter of the two lenses. Use an X-Acto knife to cut circles into the paper, then glue the lenses atop of these smaller circles.

5. Glue the paper with the shorter focal length lens to the end of the smaller telescoping tube. Glue the other lens to the end of the larger telescoping tube.

6. Look through the eyepiece (the smaller focal length lens), and slide the smaller telescoping tube into the larger telescoping tube until you see a focused image. If you can see a magnified image, you now have your own homemade refracting telescope.

Tips & Warnings

• The two mailing tubes should be a similar size, since the smaller tube must slide in and out of the larger tube.

• Ensure your lenses have a smaller diameter than the mailing tube.

References

• NASA: Build a Telescope