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Perfect collimation will yield a star image very symmetrical just inside and outside of focus. In addition, perfect
collimation delivers the optimal optical performance specifications that your telescope is built to achieve.
If seeing (i.e., air steadiness) is turbulent, collimation is difficult to judge. Wait until a better night if it is turbulent
or aim to a steadier part of the sky. A steadier part of the sky is judged by steady versus twinkling stars.
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The optical performance of most Newtonian reflecting telescopes can be optimized by re-collimating (aligning) the
telescope's optics, as needed. To collimate the telescope simply means to bring its optical elements into balance.
Poor collimation will result in optical aberrations and distortions.
Before collimating your telescope, take time to familiarize yourself with all its components. The primary mirror is
the large mirror at the back end of the telescope tube. This mirror is adjusted by loosening and tightening the three
screws, placed 120 degrees apart, at the end of the telescope tube. The secondary mirror (the small, elliptical mirror
under the focuser, in the front of the tube) also has three adjustment screws. To determine if your telescope needs
collimation first point your telescope toward a bright wall or blue sky outside.
Never look directly at the sun with the naked eye or with a telescope (unless you have the proper solar filter).
Permanent and irreversible eye damage may result.
Aligning the Secondary Mirror
The following describes the procedure for daytime collimation of your telescope using the optional Newtonian
Collimation Tool (#94183) offered by Celestron. To collimate the telescope without the Collimation Tool, read the
following section on night time star collimation. For very precise collimation, the optional Collimation Eyepiece
1 ¼” (# 94182) is offered.
If you have an eyepiece in the focuser, remove it. Rack the focuser tube in completely, using the focusing knobs,
until its silver tube is no longer visible. You will be looking through the focuser at a reflection of the secondary
mirror, projected from the primary mirror. During this step, ignore the silhouetted reflection from the primary
mirror. Insert the collimating cap into the focuser and look through it. With the focus pulled in all the way, you
should be able to see the entire primary mirror reflected in the secondary mirror. If the primary mirror is not
centered in the secondary mirror, adjust the secondary mirror screws by alternately tightening and loosening them
until the periphery of the primary mirror is centered in your view. DO NOT loosen or tighten the center screw in the
secondary mirror support, because it maintains proper mirror position.
Aligning the Primary Mirror
Now adjust the primary mirror screws to re-center the reflection of the small secondary mirror, so it’s silhouetted
against the view of the primary. As you look into the focuser, silhouettes of the mirrors should look concentric.
Repeat steps one and two until you have achieved this.
Remove the collimating cap and look into the focuser, where you should see the reflection of your eye in the
secondary mirror.
