Celestron OMNI XLT 102 Instruction Manual page 47

When satisfied with the collimation, tighten the small locking screws.
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.
Take note of the direction the light appears to flare. For example, if it appears to
flare toward the three o'clock position in the field of view, then you must move
whichever screw or combination of collimation screws necessary to move the
star's image toward the direction of the flaring. In this example, you would want
to move the image of the star in your eyepiece, by adjusting the collimation
screws, toward the three o'clock position in the field of view. It may only be
necessary to adjust a screw enough to move the star's image from the center of the
field of view to about halfway, or less, toward the field's edge (when using a high
power ocular).
Collimation adjustments are best made while viewing the star's position in the field
of view and turning the adjustment screws simultaneously. This way, you can see
exactly which way the movement occurs. It may be helpful to have two people
working together: one viewing and instructing which screws to turn and by how
much, and the other performing the adjustments.
IMPORTANT: After making the first, or each adjustment, it is necessary to re-aim the telescope tube
to re-center the star again in the center of the field of view. The star image can then be
judged for symmetry by going just inside and outside of exact focus and noting the
star's pattern. Improvement should be seen if the proper adjustments are made. Since
three screws are present, it may be necessary to move at least two of them to achieve
the necessary mirror movement.
Figure 7-7
47
Figure 7-8
A collimated telescope
should appear as
symmetrical ring pattern
similar to the diffraction
disk seen here.
a