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How to Troubleshoot a Telescope's Focus

A telescope's focus control defines the sharpness of the star's image. If the telescope is out of focus, the star will be difficult or impossible to see. Certain focusing techniques will allow you to focus correctly each time. The techniques apply to any focusing mechanism, including Schmidt-Cassegrain, and any telescope manufacturer. Problems with your focus can be corrected by following some troubleshooting steps.

Instructions

- 1
  Focus on a bright object first, like the moon or a planet. Out-of-the-box focusing is much easier if the object is easy to see. Focusing on a star can be extremely tricky, because if you turn the focus knob too fast, you can whiz through focus without seeing the star at all. Always start by focusing on an object that will be visible even if the object is out of focus.
- 2
  Turn the focus knob in the smoothest and easiest rotation. On many telescopes, such as a Schmidt-Cassegrain focusing-mechanism telescope, this will be moving the focusing mirror against the force of gravity. You'll get a much smoother rotation. Start focusing with the knob making the smoothest moves. Many focusing knobs will have an arrow-like icon showing you which way to turn. Most often this is counterclockwise.
- 3
  Stop turning the focus knob if it won't move any further -- you've probably reached the end of the focusing ability. Turn the knob in the opposite direction until the image is sharp. Turn the knob again to focus on closer or more distant objects. On a Schmidt-Cassegrain-style mirror-focus telescope, move it clockwise for closer objects and counterclockwise for farther objects.

Astronomy