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COLLIMATION PROCESS
To collimate your telescope, you'll use a Phillips-head
screwdriver to make adjustments to the collimation
screws on the back of the secondary mirror assembly.
These three screws are clearly visible when looking at
the front of most telescopes (see Figure 6).
Some older SCT telescopes have an orange cap
that covers the collimation screws (see Figure 7).
Carefully use a fl at-head instrument or other tool to
pry the cap off. There are a couple of tabs on the
plastic cap that connect it to the rear of the secondary
mirror assembly. Once the cover is removed, it's easy
to see and access the three collimation screws.
There are three collimation screws; each can be adjusted to change the tilt of the secondary mirror. All
three screws provide a "tip/tilt" adjustment system, if you loosen one screw, then the other two screws
should be tightened. Conversely, if you tighten one screw, then the other two screws should be slightly
loosened (see Figure 8). In practice, since each screw will only be loosened or tightened by a very small
amount at a time, it is not necessary to adjust all three screws at once, as there is some fl ex in the mechanical
assembly. However, if you do tighten (or loosen) one of the screws by a signifi cant amount, then the other two screws
will need to be loosened (or tightened) at some point in order to provide the proper screw tension.
WARNING: When using the screwdriver to make adjustments to the collimation screws, stay focused and be careful
not to inadvertently scratch the Schmidt corrector. Use a red-light fl ashlight, if needed, to illuminate the
collimation screws so you can make sure you put the screwdriver tip in the head of the intended screw.
The goal of making adjustments to the collimation screws is to center the central shadow (i.e. the hole) in the defocused
star image. Make only small 1/10th-of-a-turn adjustments at most to each of the collimation screws.
Collimation
Screws
Front View
4 |
SCT & EDGEHD COLLIMATION GUIDE
Secondary Mirror
Tighten
Collimation
Screws (2)
Loosen
Collimation
Screw
Side View
Collimation
Screws
Loosen
Collimation
Screws (2)
Tighten
Collimation
Screw
Fig. 6
Fig. 7
Secondary Mirror
Side View
Fig. 8
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