What You Need:
- Convex lenses with different focal lengths - 2
- A cardboard tube
- Sticky tape
- Coloured felt pen
- Take the cardboard tube and cut it to the length of the two focal lengths of the lenses. For example, if you have 10cms and 20cms lenses, you would need a 30cms tube.
- Now attach the lenses to either end of the tube using sticky tape, without obstructing the view through the tube.
- Mark the end of the tube with the shorter focal length lens so you know which direction to look through.
- Now look through the viewing end and you're looking through a telescope! You will notice that the image you see is upside down. Real telescopes have many lenses in them so the image always appears right side up.
- If you look through the telescope with one eye and look straight at the object with the other, you should be able to see both the magnified and the unmagnified images and compare the two.
- Do you see a magnification? Try and measure it.
The magnification of a telescope depends on the arrangement and the focal lengths of the lenses within it. The quality of the picture depends upon the size (diameter) of the lenses. The bigger, the better. Some of the largest telescopes have lenses over 8mts in diameter.