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ENGLISH I 19
2. Place your finger along the edge of the front cell of the telescope (be careful not to touch the corrector plate), pointing
towards the collimation screws. The shadow of your finger should be visible when looking into the eyepiece. Rotate your
finger around the tube edge until its shadow is seen closest to the narrowest portion of the rings (i.e., the same direction in
which the central shadow is skewed).
Even though the star pattern appears the same on both sides of focus, they are asymmetric. The dark obstruction is skewed
off to the left side of the diffraction pattern indicating poor collimation.
To accomplish this, you need to tighten the secondary
collimation screw(s) that move the star across the
field toward the direction of the skewed light. These
screws are located in the secondary mirror holder).
Make only small 1/6 to 1/8 adjustments to the colli-
mation screws and re-center the star by moving the
scope before making any improvements or before
making further adjustments.
To collimate your telescope, follow these steps:
1. While looking through a medium-to-high-power eyepiece,
de-focus a bright star until a ring pattern with a dark
shadow appears. Center the de-focused star and
notice in which direction the central shadow is skewed.
Secondary Mirror Collimation Adjustment Screws
The optical performance of your telescope is directly related to its collimation. Collimation is the alignment of the optical
system. Your Schmidt-Cassegrain telescope was collimated at the factory after it was completely assembled. However, the
telescope may have to be collimated after it’s transported. The only optical element that may need to be adjusted, or is
possible, is the tilt of the secondary mirror.
To check the collimation of your telescope you will need a light source. A bright star near the zenith is ideal since there is
a minimal amount of atmospheric distortion. Make sure that tracking is on so that you won’t have to manually track the star.
Or, if you do not want to power up your telescope, you can use Polaris. Its position relative to the celestial pole means that it
moves very little thus eliminating the need to manually track it.
Before you begin the collimation process, be sure that your telescope is in thermal equilibrium with the surroundings. Allow
45 minutes for the telescope to reach equilibrium if you move it between large temperature extremes.
To verify collimation, view a star near the zenith. Use your high power eyepiece — 9mm focal length. It is important to center a
star in the center of the field to judge collimation. Slowly move in and out of focus and judge the symmetry of the star. If you
see a systematic skewing of the star to one side, then re-collimation is needed.
COLLIMATION
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