How do I build a telescope at home?

In its essence, a telescope is an instrument that makes a far away object look closer. To do this, a telescope has a device that collects light from a distant object (objective lens or primary mirror) and brings that light (image) to a focus where a second device (eyepiece lens) magnifies the image and brings it to your eye. To make a simple telescope at home, you will need the following:

  • two magnifying glasses - perhaps 1 - 1.5 inches (2.5-3 cm) diameter (it works best if one is larger than the other)
  • a cardboard tube - paper towel roll or gift-wrapping paper roll (it helps if it is long)
  • duct tape
  • scissors
  • a ruler, yard stick, or tape measure
  • sheet of printed paper - newspaper or magazine will do

To assemble your telescope, do the following:

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  1. Get the two magnifying glasses and a sheet of printed paper.
  2. Hold one magnifying glass (the bigger one) between you and the paper. The image of the print will look blurry.
  3. Place the second magnifying glass between your eye and the first magnifying glass.
  4. Move the second glass forward or backward until the print comes into sharp focus. You will notice that the print appears larger and upside down.
  5. Have a friend measure the distance between the two magnifying glasses and write the distance down.
  6. Cut a slot in the cardboard tube near the front opening about an inch (2.5 cm) away. Do not cut all the way through the tube. The slot should be able to hold the large magnifying glass.
  7. Cut a second slot in the tube the same distance from the first slot as your friend wrote down. This is where the second magnifying glass will go.
  8. Place the two magnifying glasses in their slots (big one at front, little one at back) and tape them in with the duct tape
  9. Leave about 0.5 - 1 inch (1 - 2 cm) of tube behind the small magnifying glass and cut off any excess tube remaining.
  10. Check to see that it works by looking at the printed page. You may have to play slightly to get the exact distances between the two glasses right so that the image comes to a focus.

You have just built a simple refracting telescope! With your telescope, you should be able to see the moon and some star clusters as well as terrestrial objects (i.e. birds).

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Originally Published: Feb 8, 2001

Build Telescope FAQ

How much does it cost to build a telescope?
The cost really depends on the design and materials you use. However, typical materials such as mirrors, eyepieces and a finder have a minimum cost of $300 USD. It can cost less if you can find and purchase second-hand materials.
How do I make a telescope high magnification?
For high magnification, you need a greater focal length. For this, a Barlow lens can be used in the eyepiece. It’s a diverging lens that spreads out rays of light for a clearer, more magnified image.
How do you calculate the magnification of a telescope?
To determine this, you’ll need the focal length (FL) of the eyepiece and focal length of the lens.The magnification is the FL of the lens divided by the focal lengths of the eyepiece. In general, the maximum magnification of a telescope is 50 times the size of the aperture.
Do telescopes use concave or convex lenses?
The Galilean telescope uses both types of lenses: concave for the eyepiece and convex for the objective lens. On the other hand, most refractive telescopes only use convex lenses for both eyepieces and objectives, which form inverted real images of magnified objects.

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