13
Preparing the Telescope for Collimation
Once you get the hang of collimation, you will be able to do it
quickly even in the dark.
For now, it is best to collimate in daylight, preferably in a
brightly lit room and aimed at a white wall. It is recommended
that the telescope tube be oriented horizontally. This will pre-
vent any parts from the secondary mirror from falling down
onto the primary mirror and causing damage, should some-
thing come 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 collimation,
your telescope should resemble Figure 19.
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 18b, it must be
adjusted. This adjustment will rarely, if ever need to be done.
Using a 2mm hex key, loosen the three small alignment set
screws in the center hub of the 4-vaned spider 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 20).
Turning the screw clockwise will move the secondary mirror
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 18c, you will need to adjust the tilt
of the secondary mirror. This is done by alternately loosening
one of the three alignment hex screws while tightening the
other two, as depicted in Figure 21. Do not make excessive
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 mirror
reflection in the secondary mirror, as in Figure 18d. Don’t
worry that the reflection of the secondary mirror (the smallest
circle, with the collimation cap “dot” in the center) is off-cen-
ter. You will fix that in the next step.
Figure 19.
The
SkyQuest 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 20.
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 21.
Adjust the tilt of the secondary mirror by loosening or
tightening the three alignment set screws with a 2mm hex key.
