Orion SKYQUEST #27189 XT12I - Manual (Page 16)

Preparing the telescope for collimation
Once you get the hang of collimation, you will be able to do
it quickly even in the dark. When trying it for the first time or
two, though, it is best to collimate in daylight, preferably in a
brightly lit room and with the telescope 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,
should something come loose when you are making adjust-
ments. Place a sheet of white paper inside the optical tube
directly opposite the focuser. This will provide a bright “back-
ground” when viewing into the focuser. When properly set up
for collimation, your telescope should resemble
Figure 20.
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, in the direction parallel to the
length of the telescope. If it isn’t, as in
Figure 19b, it must be
adjusted. This adjustment will rarely, if ever need to be done.
Using the included 2mm hex key, loosen the three small
alignment set screws in the center hub of the 4-vaned spi-
der several turns. Now keep the mirror’s holder stationary (be
careful not to touch the surface of the mirrors), while turning
the center screw with a Phillips head screwdriver (see
Figure
21). 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.
Note: When making these adjustments, be careful not to
stress the spider vanes or they may bend.
When the secondary mirror is centered in the focuser draw-
tube, rotate the secondary 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. Now
tighten the three small alignment screws equally to secure the
secondary mirror in that position.
If the entire primary mirror reflection is not visible in the sec-
ondary mirror, as in
Figure 19c, you will need to adjust the tilt
of the secondary mirror. This is done by alternately loosen-
ing one of the three alignment hex screws while tightening
the other two, as depicted in
Figure 22. Do not make exces-
sive turns of these hex screws or force them past their normal
travel. A simple 1/2 turn of the screw can dramatically change
the tilt of the mirror. The goal is to center the primary mir-
ror reflection in the secondary mirror, as in
Figure 19d. Don’t
worry that the reflection of the secondary mirror (the smallest
circle, with the collimation cap “dot” in the center) 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 19d, 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
16
Figure 20.
The SkyQuest
XTi IntelliScope
properly set up
for collimation.
Note the white
paper placed
across from the
focuser, and
the level angle
of the optical
tube. Ideally, the
telescope should
be pointing at a
white wall.
Figure 21. 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. Do not touch the mirror’s surface!
Figure 22. Adjust the tilt of the secondary mirror by loosening or
tightening the three alignment set screws with the 2mm hex key.