Reflecting Telescope

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A Newtonian reflecting telescope model can be made from a few simple pieces of apparatus that most science laboratories will have.

Requirements per telescope:

  1. Two retort stands
  2. Three boss heads and clamps
  3. One concave mirror (a focal length of 200mm worked well in testing) A compact mirror (for cosmetics) may work
  4. One dental mirror
  5. One microscope eye piece (10x) was used in trials


The mirror is held in the jaws of a clamp so that it is facing an object of high contrast (posters on a wall do well).
The three pronged clamps are ideal as they hold the mirror better. This arrangement is held on the retort stand at a convenient height 30 cm or so of the table.
The dental mirror is held in the jaws of a second clamp on the second retort stand so that it is at the same level as the "objective" concave mirror. Move the dental mirror so that it is about 25mm from the focus of the Concave mirror. The dental mirror should be angled to 45 degrees to the path of the light between the mirror and the object, so that when looking down on the mirror a clear image of the concave mirror can be seen.
The eyepiece of the microscope is now placed carefully in the jaws of a second clamp and manoeuvred so that is about an inch above the dental mirror.
Look through the eye-piece and move the concave mirror (on the stand) back and forth to focus.

actual telescope
Schematic of a Newtonian reflecting telescope

Results and development ideas

Using the trial arrangement a magnification of about -3 (inverted) was acheived.
A "shaving mirror" may give better results but is bulky.
A bulb or other bright light can be used to show the limitations of this device. The glass causes many ghost images to be formed.
Applying a surface coat to the mirrors (e.g. using the silver mirror test) may improve the image but these will not last long and is not recommended.
The simpicity of the equipment allows a full understanding of how the telescope works.
With a suitable Astronomical mirror and optically flat reflector a "Dobsonian" telescope can be made. (categories and external links to be added)
--D.B.Ferguson 20:43, 1 February 2008 (GMT)
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