Orion 9786 instruction manual Aligning the Primary Mirror, Alignment set screws

Spider vane thumbnuts

Figure 5. To center the secondary mirror up-and-down in the focuser drawtube, make adjustments to the two knurled spider vane thumbnuts that are perpendicular to the focuser.

ary mirror holder until the reflection of the primary mirror is as centered in the secondary mirror as possible. It may not be perfectly centered, but that is OK for now. Tighten the three small alignment setscrews equally to secure the secondary mirror in that position.

To adjust the secondary mirror up-and-down in the focuser drawtube, adjust the length of the two spider vanes perpen­ dicular to the focuser. This is done by tightening the knurled thumbnuts that secure the vanes to the tube (Figure 5). Loosen one thumbnut, then tighten the other until the second­ ary mirror is centered in the drawtube.

The secondary mirror should now be centered in the focuser drawtube. Now we will shift our attention to the reflections within the secondary mirror.

If the entire primary mirror reflection is not visible in the sec­ ondary mirror, as in Figure 3c, you will need to adjust the tilt of the secondary mirror. This is done by alternately loosen­ ing one of the three alignment setscrews while tightening the other two, as depicted in Figure 6. You will need a 2mm hex key to do this. The goal is to center the primary mirror reflec­ tion in the secondary mirror, as in Figure 3d. Don’t worry that

the reflection of the secondary mirror within the primary mirror reflection (the smallest circle, with the collimation cap “dot” in the center) is off-center. You will fix that in the next step.

Once the secondary mirror is centered in the focuser draw­ tube, and the primary mirror reflection is centered in the sec­ ondary mirror, the secondary mirror is properly aligned, and no further adjustments to it should be needed.

Aligning the Primary Mirror

The final adjustment is made to the primary mirror. It will need adjustment if, as in Figure 3d, the secondary mirror is cen­ tered in the focuser drawtube and the reflection of the pri­ mary mirror is centered in the secondary mirror, but the small reflection of the secondary mirror (with the “dot” of the col­ limating cap) is off-center.

The tilt of the primary mirror is adjusted with the three large knurled thumbscrews on the rear end of the optical tube (back of the mirror cell) (Figure 7). The small thumbscrews (with slots in them) serve to lock the mirror in place. Start by loos­ ening each of these smaller thumbscrews a few turns. Use a screwdriver in the slots, if necessary. Now adjust the tilt of the primary mirror by turning one of the large thumbscrews either clockwise or counterclockwise. Look into the focuser and see if the secondary mirror reflection has moved closer to the center of the primary mirror reflection. You can determine this easily with the collimating cap and primary mirror center mark by simply watching to see if the “dot” of the collimating cap is moving closer or farther away from the “ring” on the primary mirror. If it isn’t getting closer, try turning the thumbscrew in the opposite direction. Repeat this process for the other two large thumbscrews, if necessary. It will take a little trial-and- error to get the feel for how to adjust the primary mirror to center the dot of the collimating cap in the ring of the primary mirror center mark.

When you have the dot centered as much as possible in the ring, your primary mirror is aligned. The view through the colli­ mating cap should resemble Figure 3e. Make sure the smaller thumbscrews on the back of the mirror cell are tightened to lock the primary mirror in position.

Alignment set screws (3)

Figure 6. Adjust the tilt of the secondary mirror by loosening one of the three alignment set screws then tightening the other two.

Figure 7. The tilt of the primary mirror is adjusted by turning the three larger thumbscrews.

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