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Figure 23.
The
SkyQuest optical tube
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. (IntelliScope
model shown.)
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 23.
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 22b, 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 rotating
(be careful not to touch the surface of the mirror), while turn-
ing the center screw with a Phillips head screwdriver (Figure
24). 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-
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
Figure 24.
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 25.
Adjust the tilt of the secondary mirror by loosening or
tightening the three alignment set screws with a 2mm hex key.
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 22c, you will need to adjust the tilt
of the secondary mirror. This is done by alternately loosen-
ing one of the three secondary mirror alignment set screws
while tightening the other two, as depicted in Figure 25. Do
not make excessive turns of these set screws or force them
past their normal travel. A simple 1/2 turn of the screw can dra-
matically change the tilt of the secondary mirror. The goal is to
center the primary mirror reflection in the secondary mirror, as
in Figure 22d. Don't worry that the reflection of the secondary
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