Orion 9768 Instruction Manual
INSTRUCTION MANUAL
Orion® 3.6"
Clear-Aperture Reflector
Optical Tube Assembly
Primary mirror cell
#9768
Dovetail mount Focuser
Focus knobs
Secondary mirror
holder
Figure 1. The 3.6" Clear-Aperture reflector optical tube assembly.
Congratulations on your purchase of an Orion telescope. Your new 3.6" Clear-Aperture (CA) reflector is
specifically designed for high-resolution visual observation of astronomical objects. With its unobstructed
optical system, you’ll be able to enjoy razor sharp views of objects such as planets, the Moon, double
stars, and hundreds of other fascinating celestial denizens.
About the Clear-Aperture Newtonian
Optical Design
The clear-aperture Newtonian is an exciting optical design that
has gained popularity in recent years. Because of its unobstructed primary mirror, it provides much higher image contrast
than obstructed optical designs, such as standard Newtonians
and Schmidt-Cassegrains. The secondary mirrors in those
types of telescopes block a significant portion of the incoming
light, which only serves to reduce image contrast.
In addition, since the incoming light does not pass through any
lenses, there is no chromatic aberration (color dispersion) in
clear-aperture Newtonians, as is present in refractors. In fact,
side-by-side testing shows clear-aperture Newtonians can
out perform apochromatic refractors of similar aperture that
cost over twice as much! This is because the clear-aperture
Newtonian has absolutely no chromatic aberration to speak of.
Even the most expensive apochromatic refractors have some
residual chromatic aberration, which reduces image contrast.
As a result, the SkyView Pro 3.6 CA EQ yields incredibly highcontrast images. Expect to see amazingly crisp views of the
planets, Moon, Sun (with optional solar filter, of course!), double stars, and bright star clusters.
WARNING: Never look directly at the Sun
through your telescope or its finder scope—even
for an instant—without a professionally made
solar filter that completely covers the front of
the instrument, or permanent eye damage could
result. Young children should use this telescope
only with adult supervision.
IN 242 REV A 10/04
Getting Started
The telescope will arrive in one box. We recommend keeping the box and all original packaging. In case the telescope
needs to be shipped to another location, or returned to Orion
for warranty repair, having the proper box and packaging will
help ensure your telescope will survive the journey intact. The
box also makes a good container for storing the telescope
when not in use.
In addition to the optical tube assembly, you will find a collimation cap, rear cover plate, and two cover plate thumbscrews.
Dust covers for the front opening of the tube and for the
focuser drawtube are also included.
Installing the Rear Cover Plate
The rear cover plate reduces the amount of light that can enter
the telescope from behind the mirror cell, which improves
image contrast. It can be removed prior to observing to facilitate rapid cooling of the primary mirror, which ensures the
best views through the telescope. To install the rear cover
plate (if not already on the mirror cell), simply line up the small
holes in the cover plate with two of the four threaded holes in
the rear of the mirror cell. Then, thread the cover plate thumbscrews through the cover plate and into the rear of the mirror
cell (Figure 2). The larger hole in the center of the cover plate
is a finger hole to make it easier to remove the plate.
Figure 2. Thread the cover plate thumbscrews through the rear
cover plate and into two of the threaded holes in the back of the
mirror cell.
Connecting to a Mount
Optional tube rings should be used to attach the scope to a
telescope mount. Tube rings with an inner diameter of 182mm
(7.2"), such as Orion item #7375, are needed.
Use of Optional Eyepieces and Finder Scope
The 3.6" CA reflector does not come with a finder scope or
eyepieces in order to grant the user the greatest versatility in
customizing the instrument to suit their needs.
Any Orion finder scope with a dovetail bracket can be used
with the 3.6" CA reflector. Simply unthread the thumbscrew on
the tube’s dovetail mount (Figure 1) and insert the assembled
finder scope and dovetail bracket. Then retighten the thumbscrew. Finder scope brackets that do not match the dovetail
mount will need to be attached by some other means.
The 3.6" CA reflector can use almost any 1.25" eyepiece.
Remove the cover cap from the focuser drawtube, loosen
the two thumbscrews, and insert the eyepiece. Secure the
eyepiece with the thumbscrews on the drawtube. Focus the
telescope by rotating one of the focus knobs.
Magnification & Eyepieces
Magnification, or power, is determined by the focal length of
the telescope and the focal length of the eyepiece. Therefore,
by using eyepieces of different focal lengths, the resultant
magnification can be varied.
Magnification is calculated as follows:
Telescope Focal Length (mm)
Eyepiece Focal Length (mm)
= Magnification
The 3.6" CA reflector has a focal length of 1240mm, so when
used with a 25mm eyepiece yields:
1240 mm
= 50x
25 mm
The magnification provided by a 10mm eyepiece is:
1240 mm
= 124x
10 mm
The maximum attainable magnification for a telescope is
directly related to how much light it can gather. The larger the
aperture, the more magnification is possible. In general, a figure of 50x per inch of aperture is the maximum attainable for
most telescopes. Your 3.6" CA reflector has an aperture of 3.6
inches, so the maximum magnification would be about 180x.
This level of magnification assumes you have ideal conditions
for viewing.
Keep in mind that as you increase magnification, the brightness of the object viewed will decrease; this is an inherent
principle of the laws of physics and cannot be avoided. If
magnification is doubled, an image appears four times dimmer. If magnification is tripled, image brightness is reduced
by a factor of nine!
It is quite common for an observer to own five or more eyepieces to access a wide range of magnifications. This allows
the observer to choose the best eyepiece to use depending
on the object being viewed.
Whatever you choose to view, always start by inserting your
lowest power (longest focal length) eyepiece to locate and
center the object. Low magnification yields a wide field of
view, which shows a larger area of sky in the eyepiece. This
makes acquiring and centering an object much easier. If you
try to find and center objects with high power (narrow field of
view), it’s like trying to find a needle in a haystack!
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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 galaxies 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 loosen 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 loosening 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 setscrews requires a 1.5mm hex key.
Drawtube tensioning
setscrews
Focus lock
thumbscrew
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 center 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 secondary 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 telescope 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
from falling down onto the primary mirror should something
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. leftand-right in the collimation cap), use a 2mm hex key to loosen
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