Simple Galilean Telescope (about 9x Magnification): Construction

To build a simple cardboard Galilean telescope with a magnification of approximately 9x, your materials will need to have the following specifications:

Cardboard telescoping mailing tube, with an inner and outer tube that telescopes. These can be found in most office supply stores:

• Diameter of 50 mm (about 2 inches)
• Length of 1,100 mm (43.3 inches)

Lenses, which can be purchased

• Concave-convex lens: Diameter of 49 mm, focal length of 1,350 mm
• Plano-concave lens: Diameter of 49 mm, focal length of 152 mm

Note that the focal lengths of the lenses are 1,350/152 = 8.88.
Tools

• Coping saw
• Box cutter
• Drill or electrician's punch

A telescoping mailing tube will have an inner tube that slides freely into the outer tube. Cut two pieces from the inner tube, approximately 1 to 1.5 inches (2.5 to 4 centimeters), to create spacers to hold the objective lens. A coping saw will cut the cardboard clean and straight, which is important.
The removable cap on the end of the outer tube will become the eyehole. Use the drill to make an eyehole in the center of the cap, using light pressure. It is important to keep the cut as smooth as possible. An electrician's punch will also serve.
Drill small holes around the outside of the inner tube, where the lens will be. Place the flat end of the eyepiece lens against the removable cap. Slide the lens and cap into the outer tube. Add glue through the holes, and turn the lens to spread it around. Press the tube against the lens firmly until the glue is dry. Set aside.
Cut the closed end of the outer tube. Determine the how far into the tube the lens and spacers need to sit, then drill small holes on the sides of that region. Slide the first spacer in; insert glue through the relevant hole, moving it slightly to spread it around. Keep pressure on the region until the glue has dried.
Once the first spacer is dry, slide the objective lens in, with the second spacer against it. Insert glue through the hole, spread it, and press until it is dry.
Slide the inner tube into the outer tube. The telescope can be focused by sliding the cardboard tube as necessary. Once the correct focusing distance is found, the two ends can be permanently attached with glue or tape.