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How to Make Parabolic Astronomical Mirrors

Astronomers use parabolic mirrors for light collection in reflecting telescopes. Many manufacturers and scientists also prefer concave mirrors that are parabolic, rather than spherical in shape. Parabolic mirrors avoid the problems associated with spherical aberration, an error in focusing caused by light rays reflected too far from the center of the mirror. If you want to build your own telescope from scratch, you will need to grind your own mirrors, creating concave mirrors with a parabolic shape.

Things You'll Need

Mirror blank (glass disk)
Glass grinding disk of the same size
Several types of grit, of varying fineness
Water
Light source for testing
Aluminizing vacuum chamber

Instructions

- 1
  Choose the size you want for your parabolic mirror. You want a size big enough that you can work with easily but small enough for portability and stability. A good range for homemade parabolic mirrors is four to 10 inches in diameter.
- 2
  Place wet grit between your mirror blank and your grinding disk. You do not need much grit, about half a teaspoon of wet grit works for an eight-inch mirror.
- 3
  Grind the rough, spherical shape by rubbing the grinding disk on the mirror blank in regular strokes. Turn the mirror blank every few strokes for even grinding.
- 4
  When you have a concave shape, polish the surface using finer and finer grits. For the final polish, use jeweler's rouge or cerium oxide.
- 5
  Test your mirror while still in the spherical shape. If your mirror does not focus, re-grind the mirror until you get a tight focus.
- 6
  Use a parabolic tool to alter slightly the concave surface of your parabolic mirror. By slightly straightening the curve on the edges of your mirror, you will produce a parabolic shape. Test the mirror until you get a tight focus.
- 7
  Aluminize the surface of your mirror with a vacuum chamber to provide a durable reflective surface.

Astronomy