Astronomy > Telescope > Make A Refracting Telescope

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Grade Category: Middle School

Subject Category: Astronomy

Sub Category: Telescope


Let's make a refracting telescope. Piece-o-cake.

Obtain two lenses, one with a long focal length (about 8 inches) and one with a short focal length (about 1 inch). (Your teacher will probably have to get the lenses from a school science supply company.)

Hold the small (thicker) lens (the eyepiece) close to your eyes and the larger one (the objective lens) at arm's length. By bringing the larger lens closer, an image of an object across the room will come into focus through the lenses.

When the room is in focus, ask another student or the teacher to measure the distance between the two lenses. This will help determine the overall length of your telescope.

Cut a length of cardboard tubing, such as a mailing tube, in half. This brilliant writer wonders if you could use two paper-towel rollers? Slit one section lengthwise and remove a 1/4 inch strip down the side, so that by squeezing and taping it closed, this half of the tube is slightly smaller (skinnier) than the other half.

Both sections can be wrapped with masking tape to make them sturdier, but be sure the smaller tube slides easily into the larger tube. The smaller tube will hold the eyepiece lens at the near end, and the larger tube will hold the objective lens at the far end.

Cut two rings of cardboard for each of the two ends of the tubes, and cement the lenses between two rings. This is from a sheet of cardboard, like that which forms the back of a writing tablet. The outside diameter of the rings should be a little larger than that of the lenses, and the inside diameter of the rings should be a little smaller.

Tape the lenses to the tube sections. The fit should make the tubing as light-proof as possible.

By looking through the eyepiece lens and moving the smaller tube in and out, you can magnify and focus on distant objects. The instrument you have made is called a refracting telescope. (Caution: Never look directly at the sun, either with or without a telescope.)