Reflecting Telescopes

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Reflecting Newtonian Telescope

There are many different designs for reflecting telescopes.

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Newtonian reflector

  • The Newtonian reflector uses a parabolic concave primary mirror and a flat mirror as shown in the diagram.
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  • The advantage of the Newtonian reflector over a refracting telescope is that the image does not suffer from chromatic aberration at the edges.
    • Chromatic aberration is when the light diffracts slightly when it passes through a lens.
    • This causes each colour of light to bend at slightly different angles meaning the colours are slightly split at the ends of an image.

Reflecting Cassegrain Telescope

There are many different designs for reflecting telescopes.

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Cassegrain reflector

  • The Cassegrain reflector design, shown with the path of the rays through the telescope, is similar to a Newtonian reflector in having a parabolic concave primary mirror.
  • The difference is that the secondary mirror is a convex mirror.
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  • The advantages of this design are:
    • Longer focal length than a Newtonian of a similar physical length.
    • Position of the focal point is closer to the main body of the telescope.

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