Actual Step

Step 2: Collimating the Secondary Mirror

updated: 2025-10-09

Purpose

Aligning the secondary mirror with the optical axis of the telescope

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Completion of Step 1: Adjusting the Primary Mirror

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IMPORTANT: NEVER ADJUST THE SECONDARY CENTER SCREW

Doing so will alter the focal length of the telescope and can cause spherical abberation. This spacing is set at the factory.



Secondary Mirror Collimation using a Laser Collimator for Newtonians and STCs (Schmidt Cassegrains), not applicable to RCTs

Adjusting the Secondary Mirror 

reference: Orion Ritchey-Crétien Astrographs
  • It is recommended that one of the collimation screws (e.g. the "Y" screw) be maintained in its current state, thus maintaining the mirror in its current position and changes in mirror spacing are avoided.
  • IMPORTANT: NEVER ADJUST THE SECONDARY CENTER SCREW
    Doing so will alter the focal length of the telescope and can cause spherical abberation. This spacing is set at the factory.
  • In contrast to the note on the picture above, it is sometimes necessary to slightly loosen the central screw  with a Philips screwdriver in order to tighten the X and Z screws - please only do this very carefully and then immediately retighten the X or Z screw to be tightened again (clockwise rotation).
  • However, it is always safer to loosen only one of the locking screws to allow the other two to move freely

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