Celestron PowerSeeker Série Mode D'emploi page 28

With Polaris or a bright star centered within the field of view, focus with either the standard ocular or your highest
power ocular, i.e. the shortest focal length in mm, such as a 6mm or 4mm. Another option is to use a longer focal
length ocular with a Barlow lens. When a star is in focus it should look like a sharp pinpoint of light. If, when
focusing on the star, it is irregular in shape or appears to have a flare of light at its edge, this means your mirrors
aren't in alignment. If you notice the appearance of a flare of light from the star that remains stable in location, just
as you go in and out of exact focus, then re-collimation will help sharpen the image.
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 to
achieve the necessary mirror movement.
Figure 7-2
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Figure 7-3
A collimated telescope
should appear as a
symmetrical ring pattern
similar to the diffraction
disk seen here.