Orion 9786 - Manual (Page 6)

6
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 up­and­down 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 off­center. 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 off­center.
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 trial­and­
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.
Figure 7. The tilt of the primary mirror is adjusted by turning the
three larger thumbscrews.
Figure 5. To center the secondary mirror up­and­down in the
focuser drawtube, make adjustments to the two knurled spider vane
thumbnuts that are perpendicular to the focuser.
Spider vane
thumbnuts
Figure 6. Adjust the tilt of the secondary mirror by loosening one
of the three alignment set screws then tightening the other two.
Alignment set
screws (3)