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Be sure to re-center the star in the eyepiece's fi eld of view by moving the telescope on its mount after making any
adjustments to the collimation screws. If the star is not centered in the fi eld of view, interpretation of the defocused star
images will not be accurate to determine proper collimation. As discussed previously, using shorter focal length eyepieces
will increase magnifi cation and improve the centering precision of the star within the fi eld of view of the eyepiece.
To collimate the SCT or EdgeHD, follow these steps:
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1. Center the bright star in the eyepiece's fi eld of view. Insert the highest
power eyepiece that can be used with good results under current seeing
conditions.
2. Defocus the star until you can see a dark "hole" in the center (i.e. the
shadow of the secondary mirror) and 2-4 diffraction rings of light around
it. If you defocus the star too much, it may be diffi cult to determine precise
collimation, and it will also become dimmer and harder to see. If you defocus
the star too little, you won't be able to distinctly see the hole and rings.
3. Inspect the out-of-focus ("extra-focal") diffraction pattern.
4. Next, turn the focus knob in the opposite direction. This will cause the
image to pass through focus and become defocused on the other side of
focus. Again, defocus the image until you can see the central hole and 2-4
rings of light around it.
SCT & EDGEHD COLLIMATION GUIDE |
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