Figure 15. To center the secondary mirror under the focuser, hold the secondary mirror holder in place with one hand while adjusting the center bolt with a Phillips screwdriver. Do not touch the mirror’s surface!
Figure 16. Adjust the tilt of the secondary mirror by loosening or tightening the three alignment set screws with a 2mm hex key.
Figure 17. The three small thumbscrews that lock the primary mirror in place must first be loosened before any adjustments can be made.
of the secondary mirror. This is done by alternately loosening one of the three alignment set screws while tightening the other two, as depicted in Figure 16. The goal is to center the primary mirror reflection in the secondary mirror, as in Figure 14d. Don’t worry that the reflection of the secondary mirror (the smallest circle, with the collimation cap “dot” in the cen- ter) is off-center. You will fix that in the next step.
Adjusting the Primary Mirror
The final adjustment is made to the primary mirror. It will need adjustment if, as in Figure 14d, the secondary mirror is cen- tered under the focuser and the reflection of the primary mir- ror is centered in the secondary mirror, but the small reflection of the secondary mirror (with the “dot” of the collimation cap) is
The tilt of the primary mirror is adjusted with three spring- loaded collimation thumbscrews on the back end of the opti- cal tube (bottom of the primary mirror cell); these are the larg- er thumbscrews. The other three smaller thumbscrews lock the mirror’s position in place; these thumbscrews must be loosened before any collimation adjustments can be made to the primary mirror.
Figure 18. The tilt of the primary mirror is adjusted by turning one or more of the three larger thumbscrews.
To start, turn the smaller thumbscrews that lock the primary mirror in place a few turns each (Figure 17). Use a screwdriv- er in the slots, if necessary.
Now, try tightening or loosening one of the larger collimation thumbscrews with your fingers (Figure 18). Look into the focuser and see if the secondary mirror reflection has moved closer to the center of the primary. You can tell this easily with the collimation cap and mirror center mark by simply watching to see if the “dot” of the collimation cap is moving closer or fur- ther away from the “ring” on the center of the primary mirror mark. When you have the dot centered as much as is possible in the ring, your primary mirror is collimated. The view through the collimation cap should resemble Figure 15e.
A simple star test will tell you whether the optics are accurate- ly collimated.
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