Building your own telescope is a fun optical experiment and it can be used to get a better view of the moon and other distant objects.

Materials:
1 .Lens with a short focal length 50 mm double convex lens
2. Lens with a long focal length double convex lens
3. 2 sheets of paper or cardstock
4. Tape


Procedure:
1. Roll up one sheet of paper the short way to form a tube that is about the diameter of the lens with the shortest focal length. This will be the eyepiece. Tape the edges of the eyepiece lens to one end of the tube as neatly as possible.

2. Roll up a second sheet of paper the long way around the tube you just made to form another tube that slides easily over the first one. Tape the second lens neatly to the end of this tube. Now your telescope is ready to be used!

3. Look through the eyepiece and point the other end of your telescope at a distant object. Slide the two tubes in and out until the object comes into focus. You will see the image upside down and magnified 6 times (with a 300 mm lens).

What's Happening?

You have just built a simplified version of a refractor telescope. The lenses at each end work together to focus on a distant object and magnify it so that your eye can see it better. The lens on the outside tube is called the objective lens. This lens collects light from whatever you point the telescope at. The lens at the other end of the telescope is called the eyepiece lens. It takes the light that the objective lens has collected and makes it bigger so that it takes up more space on the part of your eye that allows you to see, so that when you see the image that your telescope is focused on, you see it several times larger than you can see it with your eye alone.

Note: this project can also be done using a 500 mm focal length lens, which will provide 10 times magnification. However, because the focal length is longer, a longer paper tube will be required for the telescope to work. Try using a larger sheet of paper, or taping two sheets together before making the tube.