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How to Adjust a Reflecting Telescope

Newtonian reflector telescopes employ a two-mirror optical design first developed by Sir Isaac Newton. The primary mirror gathers light from the moon, planets and other astronomical objects. The secondary mirror then reflects the light captured by the primary mirror and redirects it to a magnifying eyepiece. The primary and secondary mirrors must be perfectly aligned for a reflector telescope to work properly. You should periodically check and adjust the alignment of these mirrors, a process called collimation.

Things You'll Need

Flashlight
Cheshire sight tube
Phillips-head screwdriver

Instructions

- 1
  Set up the telescope in a brightly lit room, or have someone shine a flashlight down the telescope's optical tube during the collimation process.
- 2
  Tilt the telescope's optical tube at a 45 degree angle. Insert the Cheshire sight tube into the telescope's focuser. Tighten the set screw on the focuser to lock the sight tube in place.
- 3
  Look through the Cheshire sight tube. Turn the focuser knob clockwise until the secondary mirror nearly fills the sight tube's field of view. Check whether the secondary mirror appears round and centered in the focuser.
- 4
  Adjust the secondary mirror's orientation if it is off-center or oval in shape. Loosen the central screw on the secondary mirror and tighten the three adjustment screws if you need to lower the secondary mirror. Otherwise, loosen the three adjustment screws on the secondary mirror and tighten the central screw to raise the secondary mirror.
- 5
  Use the three adjustment screws to tilt the secondary mirror until it appears circular in the Cheshire sight tube's field of view. Loosen one of the adjustment screws and tighten the other two and then reexamine the secondary mirror through the sight tube. Continue loosening and tightening the adjustment screws until the secondary mirror appears perfectly round.
- 6
  Look through the sight tube and examine the primary mirror's reflection in the secondary mirror. The primary mirror has a small ring marking its exact center. Check whether this center marker appears perfectly centered in the secondary mirror.
- 7
  Adjust the three thumbscrews on the bottom of the telescope's optical tube to tilt the primary mirror until its center marker appears perfectly centered in the secondary mirror.

Astronomy