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Figure 6: An example of an approximately collimated defocused star.
The CDK uses three ¼-20 socket head cap screws for collimation, as shown in Figure 7.
These screws require a 3/16 Allen wrench. It may be necessary to slightly loose the two
opposing screws in order to tighten the third screw. Remember to always finish tightening
with the secondary preloaded securely against all three screws.
Collimating is usually a two-person job: one person looks through the eyepiece while one
person adjusts the collimating screws. Attempting to do this alone can be quite difficult and
frustrating. If necessary, you might try using a webcam with a 1-1/4” nosepiece, such as the
Celestron NexImage, in place of an eyepiece. With this setup, you can watch the video
stream from the camera while you make adjustments.
Note that the central spacing knob is not used until Step 3.
.
Central Spacing Knob
Collimating screw
Figure 7: The CDK secondary housing. There are three
collimating screws and a central knob. The secondary on the
CDK is spring loaded, pulling the secondary into the three
collimating screws
