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.
1. Roll up the sheet of paper or cardstock the long 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. Tape the second lens neatly to the end of the paper towel tube. Insert the empty end of the paper tube into the cardboard 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. If you have trouble focusing the telescope, you may need to lengthen the tube, either by using a larger piece of paper for the eyepiece end or a longer cardboard tube (such as from a wrapping paper roll).
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.