Orion SkyQuest XX12g Instruction Manual page 25

Figure 32.
The SkyQuest XX12g optical tube properly set up for
collimation.
As an additional aid in collimating, the primary mirror of the
XXg has a tiny adhesive ring marking its exact center. This
center ring will not affect the images you see when observ-
ing with the telescope in any way (since it lies directly in the
shadow of the secondary mirror), but it will greatly facilitate
collimating when using the supplied collimation cap or other,
more sophisticated collimation devices, such as the Orion
LaserMate Laser Collimator.
Preparing the Telescope for Collimation
Once you get the hang of collimating, you will be able to do it
quickly even in the dark. For now, it is best to collimate in day-
light, preferably in a brightly lit room and aimed at a white wall.
It is recommended that the telescope tube be oriented hori-
zontally. This will prevent any parts from the secondary mirror
from falling down onto the primary mirror and causing damage
if something comes loose when you are making adjustments.
Place a sheet of white paper inside the optical tube directly
opposite the focuser. This will provide a bright "background"
when viewing into the focuser. When properly set up for col-
limation, your telescope should resemble Figure 32.
Aligning the Secondary Mirror
With the collimation cap in place, look through the hole in the
cap at the secondary (diagonal) mirror. Ignore the reflections
for the time being. The secondary mirror itself should be cen-
tered in the focuser drawtube. If it isn't, as in Figure 31b, its
position must be adjusted. This positional adjustment of the
secondary mirror will rarely, if ever, need to be done.
To adjust the secondary mirror left-to-right in the focuser draw-
tube, use the included 2mm hex key to loosen the three small
alignment setscrews in the center hub of the 4-vaned spider
several turns. Now, grasp the mirror to prevent it from rotat-
ing (be careful not to touch the surface of the mirror), while
turning the center screw with a Phillips screwdriver (Figure
33). Turning the screw clockwise will move the secondary mir-
ror toward the front opening of the optical tube, while turning
the screw counter-clockwise will move the secondary mirror
toward the primary mirror. When the secondary mirror is cen-
tered left-to-right in the focuser drawtube, rotate the second-
Figure 33.
To center the secondary mirror under the focuser,
hold the mirror holder in place with one hand while adjusting the
center bolt with a Phillips screwdriver.
Figure 34.
Adjust the tilt of the secondary mirror by loosening or
tightening the three alignment set screws with the supplied 2mm hex
key.
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.
NOTE: When making these adjustments, be careful not to
stress the spider vanes or they may bend.
The secondary mirror should now be centered in the focuser
drawtube. Now we will shift our attention to the reflections
within the secondary mirror in order to properly adjust the tilt
of the secondary mirror. Adjusting the tilt of the secondary
mirror and the tilt of the primary mirror are the two collimation
adjustments that will be done most often.
If the entire primary mirror reflection is not visible in the sec-
ondary mirror, as in Figure 31c, you will need to adjust the tilt
of the secondary mirror. This is done by alternately loosening
one of the three secondary mirror alignment set screws while
tightening the other two (Figure 34). Do not make excessive
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