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How to Make a Refractor

A refractor is a telescope which focuses rays of light through a convex lens. The light is magnified as it travels through this main, or objective, lens. At the other end of the telescope, is the eyepiece, where another lens or set of lenses further modifies the light to produce the image seen by the eye. The distance between the two lenses is the focal length. The curvature and size of the main lens dictates the distance needed to achieve a focal length that gives a clear image. The larger and more curved the lens, the longer the telescope must be.

Things You'll Need

2 convex lenses
2 cardboard tubes
Flat, thick cardboard
Scissors or knife
Glue
Pencil

Instructions

Use Two Tubes
- 1
  Take two cardboard tubes of slightly different diameters, the larger being about 2 inches across. They should each be about 1 foot long.
- 2
  Cut four circular rings from a piece of thick flat cardboard. Make one of them ("A") the inside diameter of the small tube. Make the other three the inside diameter of the large tube ("B", "C" and "D")
- 3
  Take two convex lenses, one about 1 ¾ inches diameter and the other about 1 inch diameter. The smaller lens is the eyepiece.
- 4
  Trace the shape of the smaller lens in the center of "A" and cut out the cardboard
- 5
  Glue the eyepiece lens into the hole.
Add the Lenses
- 6
  Glue the cardboard and lens into one end of the narrower tube.
- 7
  Cut holes in "B" and "C" so they just fit over the thinner tube.
- 8
  Glue them in place about 1 inch and 2 inches from the open end of the tube.
- 9
  Trace the shape of the larger lens in the center of "D" and cut out the cardboard.
- 10
  Glue the larger lens into the hole.
Final Assembly
- 11
  Glue the cardboard and lens into one end of the wider tube.
- 12
  Slide the eyepiece tube into the other end of the wider tube, with the "B" and "C" end going in first. It should fit snugly.
- 13
  Move the tube in and out to focus on objects.

Astronomy