Orion 9768 Instruction Manual page 3

Once you've centered the object in the eyepiece, you can
switch to higher magnification (shorter focal length eyepiece),
if you wish. This is especially recommended for small and
bright objects, like planets and double stars. The Moon also
takes higher magnifications well.
Deep-sky objects, however, typically look better at medium
or low magnifications. This is because many of them are
quite faint, yet have some extent (apparent width). Deep-sky
objects will often disappear at higher magnifications, since
greater magnification inherently yields dimmer images. This
is not the case for all deep-sky objects, however. Many galax-
ies are quite small, yet are somewhat bright, so higher power
may show more detail.
The best rule of thumb with eyepiece selection is to start
with a low power, wide field, and then work your way up in
magnification. If the object looks better, try an even higher
magnification. If the object looks worse, then back off the
magnification a little by using a lower power eyepiece.
Focuser adjustments
The metal thumbscrew on the top of the body of the focuser
(Figure 3) will lock the focuser drawtube in place once the
telescope is properly focused. Before focusing with the focus
knob, remember to first loosen this thumbscrew. Do not loos-
en the thumbscrew too much as there must be some tension
to keep the drawtube secure within the focuser.
If you find the drawtube tension when focusing is either too
tight (focus knobs are difficult to turn) or too loose (image
shifts when focusing), you can adjust it by tightening or loos-
ening the two drawtube tensioning setscrews on the focuser.
These are the two small setscrews located on either side of
the focus lock thumbscrew (Figure 3). Adjusting these set-
screws requires a 1.5mm hex key.
Drawtube tensioning
setscrews
Figure 3.
The large thumbscrew on the focuser locks the
drawtube position. The two small setscrews adjust the tension of
the focuser drawtube.
collimating (aligning the Mirrors)
Collimating is the process of adjusting the mirrors so they
are precisely aligned with each another and the telescope's
focuser. Your telescope's optics were aligned at the factory,
and should not need much adjustment unless the telescope
is handled roughly. Accurate mirror alignment is important to
ensure peak performance of your telescope, so it should be
checked regularly. Collimating is relatively easy to do and can
be done in daylight, although a final "tweak" under the stars
may improve performance somewhat.
A. The Collimation Cap and Mirror Center Mark
Your 3.6" CA reflector comes with a collimation cap. This is a
simple cap that fits on the focuser drawtube like a dust cap,
but has a small hole in the center. This helps center your eye
so that collimating is easier to perform.
In addition to the collimation cap, the primary mirror is marked
with a black spot at its exact center. This "center mark" helps
to achieve a precise optical alignment, as you don't have to
guess where the center of the primary mirror is. The cen-
ter mark is also required for best results when using other
collimating devices, such as Orion's LaserMate Collimator,
obviating the need to remove the primary mirror and mark it
yourself.
B. Aligning the Secondary Mirror
To check alignment of the secondary mirror (the small mirror
held diagonally at the front of the tube), remove the eyepiece
and look down the focuser drawtube. You should see the sec-
ondary mirror centered in the drawtube and the reflection of
the primary mirror centered in the secondary mirror, as in
Figure 4a. If anything is off-center, as in Figure 4b, you will
need to align the secondary mirror.
It helps to adjust the mirrors in a brightly lit room with the tele-
scope pointed towards a bright surface, such as white paper
or wall. Placing a piece of white paper in the telescope tube
opposite the focuser and behind the secondary mirror will also
be helpful in determining the outline of the secondary mirror
itself. The telescope tube should be oriented horizontally, as
this prevents any parts from the secondary mirror assembly
Focus lock
from falling down onto the primary mirror should something
thumbscrew
come loose.
With the collimation cap on the focuser drawtube, look
through the hole in the cap at the secondary mirror. Ignore the
reflections within the secondary mirror for the time being. The
secondary mirror itself should be centered in the collimation
cap. If it isn't, as in Figure 4b, its position must be adjusted.
This adjustment should rarely need to be done.
To center the secondary mirror in the focuser drawtube in the
direction perpendicular to the optical axis (i.e. up-and-down in
the collimation cap), you will need to loosen the two Phillips
head screws that secure the secondary mirror holder to the
tube. Move the entire secondary mirror holder within the slots
until the mirror is centered up-and-down in the collimation cap
(Figure 5a). Retighten the Phillips head screws.
To center the secondary mirror in the collimation cap in the
direction parallel to the optical axis of the telescope (i.e. left-
and-right in the collimation cap), use a 2mm hex key to loosen
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