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How to Adjust the Light Focus in a Parabolic Reflector

Newtonian reflectors consist of two mirrors that capture the light from distant objects and redirect it to a magnifying eyepiece. The primary mirror features a parabolic, or concave, mirror design. It gathers the light from the moon, planets and other astronomical objects and focuses it into a cone. The smaller, secondary mirror receives the reflected light from the primary mirror and sends it the telescope's eyepiece. Focus the reflected light with the telescope's focuser to produce sharp, clear images of the astronomical objects.

Instructions

- 1
  Set up the telescope in a dark location away from local forms of light pollution such as street lights and porch lights.
- 2
  Aim the telescope at an astronomical object. Pick a bright object such as the moon or a star if you've never looked through a telescope before.
- 3
  Look through the telescope's finder scope. Adjust the angle and direction of the telescope until you have the object centered in the finder scope.
- 4
  Remove the dust cap from the telescope's focuser. Unscrew the set screw on the focuser, and insert a magnifying eyepiece into the focuser tube. Tighten the set screw to lock the eyepiece in place. Depending on whether the eyepiece is 1.25 or 2 inches in diameter, you may have to remove the 1.25-inch eyepiece adapter from the telescope to insert a 2-inch eyepiece.
- 5
  Observe the target through the magnifying eyepiece. Adjust the angle and direction of the telescope if the object is not centered in the eyepiece's field of view. The object will appear blurry and distorted because you have not yet focused the telescope.
- 6
  Adjust the focus knob to focus the light captured by the telescope's parabolic mirror. Turn the focus knob clockwise and observe whether the object sharpens in the eyepiece. If not, turn the object counterclockwise and check whether the image improves.
- 7
  Continue turning the focus knob clockwise and counterclockwise in smaller intervals to refine the image quality. When you have the telescope perfectly focused, stars should resemble pinpoints and the moon should reveal craters and other details.

Astronomy