- Two empty paper towel tubes
- Masking tape
- 2 convex lenses. Lenses from an old pair of reading glasses. Make sure the glasses are reading glasses and not glasses for helping to see things far away. You may also use lenses from magnifying glasses, or order convex lenses online.
- Choose one of your tubes to be the inner tube. Cut that tube lengthwise (all the way up the side). Wrap one edge of the cut side slightly over the other edge and hold it in place with one hand.
- Insert the cut tube into the other paper towel tube. Let go of the inner tube so that it can expand inside the outer tube. If the inner tube doesn’t slide smoothly, remove it and wrap the edge slightly tighter. Then, reinsert the inner tube into the other paper towel tube until it easily slides in and out.
- Using masking tape, secure one of the lenses to the outer edge of the inner tube. The curve of the lens should be facing the inside of the tube.
- Secure the second lens to the outer edge of the second tube, with the curve of the lens pointing outside of the tube. It’s OK if your lenses are bigger than the tube. Try to only tape around the rim of the lenses so you don’t cover too much.
- Place your eye against the lens of the inner tube. Aim your telescope at faraway animals or tall treetops (but never use a telescope to look at the Sun). Focus by sliding the inner tube in and out until the image becomes clear.
- You are now ready to observe distant buildings, the Moon, stars, or planets. NOTE: Do not use a telescope to look at the Sun.
You have just constructed a “refracting” telescope. A refracting telescope uses lenses to help gather more light. This involves using two lenses to bend light, which makes an object appear closer than it really is. The size of the image produced by the telescope depends on the curvature of the lenses. Lenses with different curvatures will change the magnification of the telescope. You may wish to experiment with lenses with different magnification factors.