Collimation - Celestron NexStar 90 MAK Instruction Manual

To collimate your telescope, remove the diagonal and eyepiece and look into rear opening of the tube (also remove the
dust cover from the front of the tube). This can be done indoors, with the telescope pointed at a white wall in a well-lit
room. Try to keep your eye centered with respect to the rear opening of the tube as best as possible. Using a Collimating
Eyepiece will aid greatly in keeping your eye centered and is strongly recommend (see Accessories section).
Secondary mirror
Front of
telescope
Secondary
reflection of
inside of tube
Figure 6-2
Out of collimation (alignment) optics as seen through the
rear of the telescope.
Once you are ready to collimate, look into rear opening of the tube. If your telescope is out of collimation, it will resemble
Figure 6-2. A properly collimated scope will resemble Figure 6-3. The direction of the misalignment in your telescope
may differ from Figure 6-2 but the diagram will give you the general idea of how things will look.
Note there are six alignment screws on the back of the optical tube, three large and three small. You will need 3mm and
2mm Allen wrenches to turn these screws. These alignment screws push and pull the mirror cell in order to tilt it. When
you loosen or tighten one of these screws, the other five screws must be adjusted as well to keep the proper amount of
pressure on the back of the mirror cell.
Look into the rear opening of the tube and locate the black crescent that
shows the telescope is out of alignment (Figure 6-2). Note which way the
front of the telescope would need to move in order to "fill" that black
crescent and resemble Figure 6-3 Then look at the back end of the
telescope and locate the alignment screw that is in the direction that the
front of the telescope needs to move. For example, if the view in your
telescope resembled Figure 6-2 then you would want to move the front
opening of the telescope scope to the right. The alignment screw you
would start with would be the screw on the right as shown in Figure 6-4.
Repeat the above steps until the front opening is centered in the direction
you wanted it to go and the view through the rear cell looks like Figure 6-
3. You may need to repeat this process with the other screws in order to
align it in other directions.
Tips for Collimating
- If you feel any resistance while turning a screw, stop immediately and loosen the two screws on either side of the one
you are turning.
- Only make small adjustments to each screw; turning them only ¼ turn at a time.
- If your telescope appears collimated after star testing, it should not need adjustment again unless it is roughly
handled.
Reflection of your
eye in Secondary
Reflection of
inside of tube
(Misalignment)
31
Secondary mirror
Front of
telescope
Figure 6-3
Collimated (aligned) optics as seen through the rear of the
telescope.
Reflection of
your eye in
secondary
mirror
"Push"

Collimation

Screws
"Pull"
Collimation
Screws
Figure 6-4