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Narrator: I am going to walk you through how to build a simple cardboard

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telescope. The body of the telescope is made from two cardboard tubes

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that nest together. Here we have a plastic cap, an optional cardboard

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washer of about the same diameter, and a convex lens, also of the same diameter.

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For the other end of the telescope, we have a piece of foam with a hole in it,

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a cardboard spacer sized to fit inside the piece of foam, and another smaller

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convex lens. First we will construct the objective

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end of the telescope, which points at the thing you want to look at.

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Start by placing the plastic cap on a table with the small lip

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on the bottom. If you have a cardboard washer, put it inside the cap.

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The lens is curved on one side and flat on the other. You

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can determine which is which by rocking it gently on a soft surface, trying to touch only

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the edges if possible. You will want to put it inside the cap with the

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curved side down. You should then fit the cap onto the end of the larger tube.

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Now we want to construct the eyepiece end of the telescope, which is the end you

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will look through. Start by placing the piece of foam

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down on a the table. Put the cardboard spacer into the hole in the foam and

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push it all the way down, until it's flush with the bottom of the hole.

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The small lens may also be curved on one side and flat on the other, but it's much

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easier to tell in this case.

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Push the lens down into the hole on top of the spacer,

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this time with the flat side down--if there is one. Now put the small end of the telescope

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down over the foam piece so it's all flush on one side.

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Since you will probably be using your telescope indoors, one of the best things

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to use to experiment with focus is a clear light bulb.

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To do this, you should replace the eyepiece end of the telescope with

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a piece of white tissue paper, held in place with a rubber band.

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Point your telescope at a clear light bulb and look at--not through-- the tissue paper.

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By sliding the smaller tube in and out of the larger tube, you can bring an

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image of the light bulb's filament into focus on the tissue paper.

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Because of the simple nature of these telescopes, all of your images will appear to be

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inverted.

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