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How to Tell When a Telescope Needs to Be Collimated

Reflector telescopes, including Newtonian reflectors, consist of four main parts: body tube, primary reflector mirror, secondary mirror and eyepiece. Reflector telescopes' primary mirrors are mounted on adjustable brackets at the rear of the telescope to allow for fine-tuning as the mirror goes out of alignment with use. This adjustment is called "collimation." To determine if the telescope is in need of collimation, it must be aimed at a distant bright object, which must be brought out of focus. Once out of focus, observation can determine if collimation is necessary for the best view.

Instructions

- 1
  Set up the telescope outdoors at night after sundown. Allow the telescope to sit for at least one full hour to allow the mirrors and lens to come to the same outdoor temperature.
- 2
  Aim the telescope at a bright star and adjust the telescope so the star is in the exact center of the eyepiece when looking through it. Focus the telescope normally to bring the star into sharp focus. Adjust the telescope further, if necessary, so the focused star is centered perfectly in view.
- 3
  Slowly rotate the focus knob to bring the star out of focus. Rotate the knob back and forth until a dark disk in the center of the unfocused star is at its largest.
- 4
  Observe the dark disk in the center of the light of the unfocused star. If the disk is in the absolute center of the circle of light, the telescope isn't in need of collimation adjustment. If the dark circular disk is off to the side, top or bottom of the circle of light, the mirrors aren't in alignment and that the telescope is in need of collimation adjustment.

Astronomy