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How to Build a Refractor Telescope

The refracting telescope is a simple device magnifying objects so they may appear closer. The basic design incorporates two lenses inside a tubular body capable of changing length. The objective lens is directed toward the object and viewed through the eyepiece lens. Magnification is determined by the ratio of combined focal length of both lenses to the focal length of the eyepiece. A simple refracting telescope can be constructed from supplies available at most office supply stores. Lenses can be found from educational or science supply stores. Building a refracting telescope is relatively simple and a great educational project.

Things You'll Need

Convex lens, 10 mm focal length
Convex lens, 50 mm focal length
Small flashlight
Ruler or tape measure
Cardboard mailing tubes, one tube with slightly smaller diameter
Serrated knife
Corrugated cardboard
Scissors
School glue
Tape, optional

Instructions

- 1
  Determine the focal length for the convex lenses. Focal length can be determined by shining a light source through the lens onto a nearby wall. The lens is moved toward or away from the wall until the light becomes a small point. The distance between the lens and the wall is the focal length.
- 2
  Add the focal lengths for the objective lens and the eyepiece lens to determine total focal length. This will be the approximate length of the telescope.
- 3
  Cut each cardboard tube half the distance of the total focal length plus 1 inch using a serrated knife. The tubes will form the body of the telescope and need additional length to allow adjustments in length for more distant or closer objects.
- 4
  Cut corrugated cardboard in circles with scissors to fit on the ends of each tube. Each tube can be placed on the cardboard and used to measure the size of the circle.
- 5
  Cut a circle in the center of each corrugated circle slightly smaller than the lenses. Each lens should have a tight fit when inserted in this hole.
- 6
  Glue the objective lens and ocular lens in the corrugated cardboard circles.
- 7
  Glue each corrugated cardboard cutout on the end of the appropriate tube. Allow the glue to dry completely.
- 8
  Insert the smaller tube into the larger tube to complete the telescope. The fit should be snug but allow the smaller tube to move freely inside the larger tube. Tape can be placed around the smaller tube to increase circumference and tighten the fit if necessary. The refractive telescope is complete and ready to use. Magnification will be a ratio of 60 mm over 10 mm, or six times.

Astronomy