Orion 9768 Instruction Manual page 6

Figure 9.
The tilt of the primary mirror is adjusted by turning one
or more of the three larger thumbscrews.
D. Using an Optional Laser Collimator
Optional laser collimators, like the Orion LaserMate, can great-
ly aid in aligning the 3.6" CA reflector's optics. Laser collimators
only help to adjust the tilt of the mirrors, so centering the sec-
ondary mirror must be done with the collimation cap. Use the
procedure described previously to do this. Once the secondary
mirror itself is accurately centered in the collimation cap, use
the following procedure to adjust the tilt of both mirrors:
1. Place the laser collimator into the focuser drawtube, and
secure it with the thumbscrews on the drawtube.
2. Turn the laser pointer on.
3. Hold a white sheet of paper over the front of the telescope
to determine where the exiting laser beam is currently posi-
tioned. Avoid placing your eye in this area while making
collimation adjustments. Remove the sheet of paper.
4. Look down the tube, and see where the laser beam reflects
off the primary mirror. This reflection will appear as a red
spot on the primary mirror (or somewhere else within the
tube if the secondary mirror tilt is very misaligned). Make
adjustments to the three setscrews that adjust the tilt of the
secondary mirror (Figure 6) until the laser spot is centered
on the primary mirror's center mark. The secondary mirror
is now collimated.
5. To adjust the tilt of the primary mirror, you will need to make
a collimation target for the front opening of the telescope
tube. This can be done by placing the telescope's dust
cover on a piece of paper and tracing the dust cover's out-
line. Make the outline a circle; do not trace the dust cover's
removal tabs. Cut the circle out, and precisely fold it in half.
Then fold the half-circle precisely in half again, to create
precise quarter circles. Unfold the circle, and mark the
intersection of the folds with a black pen; this is the precise
center of the target.
6. Center the target on the front opening of the telescope, and
tape it onto the tube so it is secure (Figure 7).
6
7. Unlock the three primary mirror lock thumbscrews (Figure
8), and use the three primary mirror collimation thumb-
screws (Figure 9) to center the exiting laser beam onto the
center of the target.
8. Retighten the primary mirror lock thumbscrews, and
remove the target from the tube. The primary mirror is now
collimated.
A simple star test will tell you whether the optics are, in fact,
accurately aligned with each other and the focuser. This is
recommended, as some slight "tweaks" to the telescope's col-
limation may be needed for optimal performance.
E. Star-Testing the Telescope
When it is dark, point the telescope at a bright star and accu-
rately center it in the 10mm eyepiece's field of view. Slowly
defocus the image with the focusing knob. If the telescope is
accurately collimated, the expanding disk should be a circle
(Figure 10). If the image is unsymmetrical (i.e. oblong or oval),
the telescope is somewhat out of collimation.
Out of collimation
Figure 10.
A star test will determine if a telescope's optics are
properly collimated. An unfocused view of a bright star through
the eyepiece should appear as illustrated on the right if the optics
are perfectly collimated. If the circle is unsymmetrical, as in the
illustration on the left, the scope needs collimation.
If you try the star test and the bright star you have selected is
not centered in the eyepiece, the optics will always appear out
of collimation, even though they may be perfectly aligned. It is
critical to keep the star centered, so over time you will need to
make slight corrections to the telescope's position in order to
account for the sky's apparent motion.
For clear-aperture Newtonians, such as the 3.6" CA reflector,
collimation errors produce astigmatism in the optical system.
If you believe your telescope's mirrors are collimated, yet out-
of-focus star images still appear slightly oblong, you may need
to "tweak" the collimation of the primary mirror slightly. Do this
by only adjusting the primary mirror collimation thumbscrew
that is in line with the focuser (Figure 11). Loosen the three
collimation lock thumbscrews (Figure 8) and turn the in line
collimation thumbscrew approximately one-quarter turn clock-
wise or counterclockwise, re-center the star in the eyepiece,
and perform the star test again. Continue making small adjust-
ments to this thumbscrew only until the star appears round
when defocusing. Retighten the collimation lock thumbscrews
when done.
Collimated