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INSTRUCTION MANUAL
Orion®
AstroView
#9024 Equatorial Refracting Telescope
™
90mm EQ
Providing Exceptional Consumer Optical Products Since 1975
Customer Support (800) 676-1343
E-mail: support@telescope.com
Corporate Offices (831) 763-7000
P.O. Box 1815, Santa Cruz, CA 95061
IN 112 Rev. C 05/02
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Tube ring mounting plate
Dec. lock knob
Dec. setting circle
R.A. lock knob
R.A. slow-motion control
Counterweight lock knob
Counterweight shaft
Counterweight
Latitude locking T-bolt
Azimuth lock knob
Accessory tray bracket
attachment point
Piggyback camera adapter
Tube mounting rings
Finder scope bracket
Finder scope
Alignment screws (2)
Eyepiece
Star diagonal
Focus knob
Dec. slow-motion control
R.A. setting circle
Latitude adjustment T-bolt
Accessory tray bracket
Tripod leg lock knob
2
Accessory tray
Figure 1. AstroView 90 EQ Parts Diagram
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Congratulations on your purchase of a quality Orion telescope. Your new AstroView 90mm EQ Refractor is
designed for high-resolution viewing of astronomical objects. With its precision optics and equatorial mount, you’ll be able to
locate and enjoy hundreds of fascinating celestial denizens, including the planets, Moon, and a variety of deep-sky galaxies,
nebulas, and star clusters.
If you have never owned a telescope before, we would like to welcome you to amateur astronomy. Take some time to familiarize yourself with the night sky. Learn to recognize the patterns of stars in the major constellations; a star wheel, or planisphere,
available from Orion or from your local telescope shop, will greatly help. With a little practice, a little patience, and a reasonably
dark sky away from city lights, you’ll find your telescope to be a never-ending source of wonder, exploration, and relaxation.
These instructions will help you set up, properly use, and care for your telescope. Please read them over thoroughly before
getting started.
Table of Contents
1. Parts List. . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Balancing the Telescope. . . . . . . . . . . . . . . 5
4. Aligning the Finder Scope . . . . . . . . . . . . . 6
5. Setting Up and Using the
Equatorial Mount . . . . . . . . . . . . . . . . . . . . 6
6. Using Your Telescope—
Astronomical Observing . . . . . . . . . . . . . . 10
7. Astrophotography . . . . . . . . . . . . . . . . . . . 13
8. Terrestrial Viewing . . . . . . . . . . . . . . . . . . 14
9. Care and Maintenance . . . . . . . . . . . . . . . 14
10. Specifications . . . . . . . . . . . . . . . . . . . . . . 14
1. Parts List
Qty. Description
1 Optical tube assembly
1 German-type equatorial mount
2 Slow-motion control cables
1 Counterweight
1 Counterweight shaft
3 Tripod legs
1 Accessory tray with mounting hardware
1 Accessory tray bracket
2 Optical tube mounting rings (located on optical tube)
1 6x30 achromatic crosshair finder scope
1 Finder scope bracket with O-ring
1 Mirror star diagonal (1.25")
1 25mm (36x) Sirius Plössl eyepiece (1.25")
1 10mm (91x) Sirius Plössl eyepiece (1.25")
1 Objective lens dust cap
4 Assembly Tools (2 wrenches, Phillips-head
screwdriver, flat-head screwdriver key)
2. Assembly
Carefully open all of the boxes in the shipping container.
Make sure all the parts listed in the parts list are present.
Save the boxes and packaging material. In the unlikely event
that you need to return the telescope, you must use the original packaging.
Assembling the telescope for the first time should take about
30 minutes. No tools are needed other than the ones provided. All screws should be tightened securely to eliminate
flexing and wobbling, but be careful not to over-tighten or
the threads may strip. Refer to Figure 1 during the assembly
process.
During assembly (and anytime, for that matter), Do not touch
the surfaces of the telescope objective lens or the lenses of
the finder scope or eyepieces with your fingers. The optical
surfaces have delicate coatings on them that can easily be
damaged if touched inappropriately. Never remove any lens
assembly from its housing for any reason, or the product
warranty and return policy will be void.
1. Lay the equatorial mount on its side. Attach the tripod
legs one at a time to the mount using the screws installed
in the tops of the tripod legs. Remove the screw from the
leg, line up the holes in the top of the leg with the holes
in the base of the mount, and reinstall the screw so it
passes through the leg and the mount. Make sure that a
washer is between the screw head and the tripod leg and
between the wingnut and tripod leg. Tighten the wingnuts
only finger-tight, for now. Note that the accessory tray
bracket attachment point on each leg should face inward.
2. Tighten the leg lock knobs at the base of the tripod legs.
For now, keep the legs at their shortest (fully retracted)
length; you can extend them to a more desirable length
later, after the scope is completely assembled.
3. With the tripod legs now attached to the equatorial mount,
stand the tripod upright (be careful!) and spread the legs
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.
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Focus
lock-ring
Alignment thumbscrews
Tensioner
Figure 2a.
The 6x30 finder scope and bracket
apart enough to connect each end of the accessory tray
bracket to the attachment point on each leg. Use the
screw that comes installed in each attachment point to do
this. First remove the screw, then line up one of the ends
of the bracket with the attachment point and reinstall the
screw. Make sure the accessory tray bracket is oriented
so that the ribs in its plastic molding face downward.
4. Now, with the accessory tray bracket attached, spread
the tripod legs apart as far as they will go, until the bracket is taut. Attach the accessory tray to the accessory
tray bracket with the three wingnut-head screws already
installed in the tray. This is done by pushing the screws
up through the holes in the accessory tray bracket, and
then threading them into the holes in the accessory tray.
5. Next, tighten the screws at the tops of the tripod legs, so
the legs are securely fastened to the equatorial mount.
Use the larger wrench and your fingers to do this.
6. Orient the equatorial mount as it appears in Figure 1,
at a latitude of about 40, (i.e., so the pointer next to the
latitude scale—located directly above the latitude locking
T-bolt—is pointing to the mark at “40.”) To do this, loosen
the latitude locking T-bolt, and turn the latitude adjustment
T-bolt until the pointer and the “40” line up. Then tighten
the latitude locking T-bolt. The declination (Dec.) and right
ascension (R.A.) axes may need repositioning (rotation)
as well. Be sure to loosen the R.A. and Dec. lock knobs
before doing this. Retighten the R.A. and Dec. lock knobs
once the equatorial mount is properly oriented.
7. Slide the counterweight onto the counterweight shaft.
Make sure the counterweight lock knob is adequately
loosened so the metal pin the knob pushes against
(inside the counterweight) is recessed enough to allow
the counterweight shaft to pass through the hole in the
counterweight.
8. Now, with the counterweight lock knob still loose, grip the
counterweight with one hand and thread the shaft into the
Figure 2b. Inserting the finder scope into the finder scope bracket
equatorial mount (at the base of the declination axis) with
the other hand. When it is threaded as far in as it will go,
position the counterweight about halfway up the shaft and
tighten the counterweight lock knob.
9. Attach the two tube rings to the equatorial head using the
screws that come installed in the bottom of the rings. First
remove the screws. then push the screws, with the washers still attached, up through the holes in the tube ring
mounting plate (on the top of the equatorial mount) and
re-thread them into the bottom of the tube rings. Tighten
the screws securely with the smaller wrench. Open the
tube rings by first loosening the knurled ring clamps.
10. Lay the telescope optical tube in the tube rings at about
the midpoint of the tube’s length. Rotate the tube in the
rings so the focus knobs are on the underside of the
telescope. Close the rings over the tube and tighten the
knurled ring clamps finger-tight to secure the telescope in
position.
11. Now attach the two slow-motion cables to the R.A. and
Dec. worm gear shafts of the equatorial mount by positioning the thmb screw on the end of the cable over the
indented slot on the worm gear shaft. Then tighten the
thumb screw.
12. To place the finder scope in the finder scope bracket, first
unthread the two black nylon screws until the screw ends
are flush with the inside diameter of the bracket. Place
the O-ring that comes on the base of the bracket over the
body of the finder scope until it seats into the slot on the
middle of the finder scope. Slide the eyepiece end (narrow end) of the finder scope into the end of the bracket’s
cylinder opposite the adjustment screws while pulling the
chrome, spring-loaded tensioner on the bracket with your
fingers (Figure 2b). Push the finder scope through the
bracket until the O-ring seats just inside the front opening
of the bracket’s cylinder. Now, release the tensioner and
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Figure 3a. Balancing the telescope with respect to the R.A.axis
by sliding the counterweight along its shaft.
Figure 3b. The telescope is now balanced on the R.A. axis.
That-is, when hands are released, the counterweight shaft remains
horizontal
Figure 3c. Preparing the telescope to be balanced on the Dec.
axis by first releasing the Dec. lock knob.
tighten the two black nylon screws a couple of turns each
to secure the finder scope in place.
13. Insert the base of the finder scope bracket into the
dovetail slot on the top of the focuser housing. Lock the
bracket in position by tightening the knurled thumbscrew
on the dovetail slot.
14. Insert the chrome barrel of the star diagonal into the
focuser drawtube and secure with the thumbscrew on the
drawtube.
15. Then insert an eyepiece into the star diagonal and secure
it in place with the thumbscrews on the diagonal. (Always
loosen the thumbscrews before rotating or removing the
diagonal or an eyepiece.)
3. Balancing the Telescope
To insure smooth movement of the telescope on both axes
of the equatorial mount, it is imperative that the optical tube
be properly balanced. We will first balance the telescope with
respect to the R.A. axis, then the Dec. axis.
1. Keeping one hand on the telescope optical tube, loosen
the R.A. lock knob. Make sure the Dec. lock knob is
locked, for now. The telescope should now be able to
Figure 3d. Balancing the telescope with respect to the Dec. axis.
As shown here, the telescope is out of blance (tilting).
Figure 3e. Telescope is now balanced on the Dec. axis, i.e., it
remains horizontal when hands are released.
rotate freely about the R.A. axis. Rotate it until the counterweight shaft is parallel to the ground (i.e., horizontal).
2. Now loosen the counterweight lock knob and slide the
weight along the shaft until it exactly counterbalances the
telescope (Figure 3a). That’s the point at which the shaft
remains horizontal even when you let go with both hands
(Figure 3b).
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3. Retighten the counterweight lock knob. The telescope is
now balanced on the R.A. axis.
4. To balance the telescope on the Dec. axis, first tighten
the R.A. lock knob, with the counterweight shaft still in the
horizontal position.
5. With one hand on the telescope optical tube, loosen the
Dec. lock knob (Figure 3c). The telescope should now be
able to rotate freely about the Dec. axis. Loosen the tube
ring clamps a few turns, until you can slide the telescope
tube forward and back inside the rings (this can be aided
by using a slight twisting motion on the optical tube while
you push or pull on it) (Figure 3d).
6. Position the telescope in the mounting rings so it remains
horizontal when you carefully let go with both hands. This
is the balance point for the optical tube with respect to the
Dec. axis (Figure 3e).
7. Retighten the tube ring clamps.
The telescope is now balanced on both axes. Now when you
loosen the lock knob on one or both axes and manually point
the telescope, it should move without resistance and should
not drift from where you point it.
Once the target object is centered on the crosshairs of the
finder scope, look again in the main telescope’s eyepiece
and see if it is still centered there as well. If it isn’t, repeat the
entire process, making sure not to move the main telescope
while adjusting the alignment of the finder scope.
The finder scope is now aligned and ready to be used for
an observing session. The finder scope and bracket can
be removed from the dovetail slot for storage, and then reinstalled without changing the finder scope’s alignment.
Focusing the Finder Scope
If, when looking through the finder scope, the images appear
somewhat out of focus, you will need to refocus the finder
scope for your eyes. Loosen the lock ring located behind the
objective lens cell on the body of the finder scope (Figure
2a). Back the lock ring off by a few turns, for now. Refocus
the finder scope on a distant object by threading the objective lens cell in or out on the finder scope body. Precise
focusing will be achieved by focusing the finder scope on a
bright star. Once the image appears sharp, retighten the lock
ring behind the objective lens cell. The finder scope’s focus
should not need to be adjusted again.
4. Aligning the Finder-Scope
A finder scope has a wide field of view to facilitate the location of objects for subsequent viewing through the main telescope, which has a much narrower field of view. The finder
scope and the main telescope must be aligned so they point
to exactly the same spot in the sky.
Alignment is easiest to do in daylight hours. First, insert the
lowest-power (25mm) eyepiece into the star diagonal. Then
loosen the R.A. and Dec. lock knobs so the telescope can be
moved freely.
Point the main telescope at a discrete object such as the top
of a telephone pole or a street sign that is at least a quartermile away. Move the telescope so the target object appears
in the very center of the field of view when you look into the
eyepiece. Now tighten the R.A. and Dec. lock knobs. Use the
slow-motion control knobs to re-center the object in the field
of view, if it moved off-center when you tightened the lock
knobs.
Now look through the finder scope. Is the object centered in
the finder scope’s field of view, (i.e., at the intersection of the
crosshairs)? If not, hopefully it will be visible somewhere in
the field of view, so that only fine adjustment of the two finder
scope alignment thumb screws will be needed to center it
on the crosshairs. Otherwise you’ll have to make coarser
adjustments to the alignment screws to redirect the aim of
the finder scope.
Note: The image seen through the finder scope appears
upside down. This is normal for astronomical finder
scopes. The image through the telescope will be inverted
left-to-right, which it normal for telescopes that utilize a
star diagonal.
5. Setting Up and Using the
Equatorial Mount
When you look at the night sky, you no doubt have noticed
that the stars appear to move slowly from east to west over
time. That apparent motion is caused by the Earth’s rotation (from west to east). An equatorial mount (Figure 4) is
designed to compensate for that motion, allowing you to
easily “track” the movement of astronomical objects, thereby
keeping them from drifting out of the telescope’s field of view
while you’re observing.
This is accomplished by slowly rotating the telescope on its
right ascension (polar) axis, using only the R.A. slow-motion
cable. But first the R.A. axis of the mount must be aligned
with the Earth’s rotational (polar) axis—a process called
polar alignment.
Polar Alignment
For Northern Hemisphere observers, approximate polar
alignment is achieved by pointing the mount’s R.A. axis
at the North Star, or Polaris. It lies within 1 degree of the
north celestial pole (NCP), which is an extension of the
Earth’s rotational axis out into space. Stars in the Northern
Hemisphere appear to revolve around Polaris.
To find Polaris in the sky, look north and locate the pattern
of the Big Dipper (Figure 5). The two stars at the end of the
“bowl” of the Big Dipper point right to Polaris.
Observers in the Southern Hemisphere aren’t so fortunate to
have a bright star so near the south celestial pole (SCP). The
star Sigma Octantis lies about 1 degree from the SCP, but it
is barely visible with the naked eye (magnitude 5.5).
For general visual observation, an approximate polar alignment is sufficient:
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R.A. lock knob
RIGHT ASCENSION AXIS
RIGHT ASCENSION AXIS
Declination (Dec.)
slow motion control
Latitude adjustment T-bolt
Azimuth lock knob
Figure 4. The equatorial mount.
1. Level the equatorial mount by adjusting the length of the
three tripod legs.
2. Loosen the latitude locking T-bolt. Turn the latitude adjusting T-bolt and tilt the mount until the pointer on the latitude scale is set at the latitude of your observing site. If
you don’t know your latitude, consult a geographical atlas
to find it. For example, if your latitude is 35° North, set the
pointer to +35. Then retighten the latitude locking T-bolt.
The latitude setting should not have to be adjusted again
unless you move to a different viewing location some distance away.
3. Loosen the Dec. lock knob and rotate the telescope optical tube until it is parallel with the R.A. axis. The pointer
on the Dec. setting circle should read 90°. Retighten the
Dec. lock knob.
4. Loosen the azimuth lock knob and rotate the entire equatorial mount left-to-right so the telescope tube (and R.A.
axis) points roughly at Polaris. If you cannot see Polaris
directly from your observing site, consult a compass and
rotate the equatorial mount so the telescope points North.
Retighten the azimuth lock knob.
The equatorial mount is now approximately polar-aligned
for casual observing. More precise polar alignment is
required for astrophotography. Several methods exist and are
described in many amateur astronomy reference books and
astronomy magazines.
Note: From this point on in your observing session, you
should not make any further adjustments in the azimuth
or the latitude of the mount, nor should you move the
tripod. Doing so will undo the polar alignment. The telescope should be moved only about its R.A. and Dec.
axes.
Declination (Dec.)
DECLINATION AXIS
setting circle
Right ascension
(R.A.) setting circle
Right ascension (R.A.)
slow motion control
Latitude locking T-bolt
Latitude scale
Little Dipper
(in Ursa Minor)
Big Dipper
(in Ursa Major)
Pointer Stars
Figure 5. To find Polaris in the night sky, look north
and find the Big Dipper. Extend an imaginary line from the two
“Pointer Stars” in the bowl of the Big Dipper. Go about five times the
distance between those stars and you’ll reach Polaris, which lies
within 1° of the north celestial pole (NCP).
Use of the R.A. and Dec.
Slow-Motion Control Cables
The R.A. and Dec. slow-motion control cables allow fine
adjustment of the telescope’s position to center objects
within the field of view. Before you can use the cables, you
must manually “slew” the mount to point the telescope in the
vicinity of the desired target. Do this by loosening the R.A.
and Dec. lock knobs and moving the telescope about the
mount’s R.A. and Dec. axes. Once the telescope is pointed
somewhere close to the object to be viewed, retighten the
mount’s R.A. and Dec. lock knobs.
The object should now be visible somewhere in the telescope’s finder scope. If it isn’t, use the slow-motion controls
to scan the surrounding area of sky. When the object is
visible in the finder scope, use the slow-motion controls to
center it. Now, look in the telescope with a long focal length
(low magnification) eyepiece. If the finder scope is properly
Pola ris
Cassiopeia
N.C.P.
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aligned, the object should be visible somewhere in the field
of view.
Once the object is visible in the telescope’s eyepiece, use
the slow-motion controls to center it in the field of view. You
can now switch to a higher magnification eyepiece, if you
wish. After switching eyepieces, you can use the slow-motion
control cables to re-center the image, if necessary.
The Dec. slow-motion control cable can move the telescope
a maximum of 25°. This is because the Dec. slow-motion
mechanism has a limited range of mechanical travel. (The
R.A. slow-motion mechanism has no limit to its amount of
travel.) If you can no longer rotate the Dec. control cable in
a desired direction, you have reached the end of travel, and
the slow-motion mechanism should be reset. This is done by
first rotating the control cable several turns in the opposite
direction from which it was originally being turned. Then,
manually slew the telescope closer to the object you wish
to observe (remember to first loosen the Dec. lock knob).
You should now be able to use the Dec. slow-motion control
cable again to fine adjust the telescope’s position.
Tracking Celestial Objects
When you observe a celestial object through the telescope,
you’ll see it drift slowly across the field of view. To keep it in
the field, if your equatorial mount is polar-aligned, just turn
the R.A. slow-motion control. The Dec. slow-motion control is
not needed for tracking. Objects will appear to move faster at
higher magnifications, because the field of view is narrower.
Optional Motor Drives for Automatic Tracking
and Astrophotography
An optional DC motor drive can be mounted on the R.A. axis
of the AstroView’s equatorial mount to provide hands-free
tracking. Objects will then remain stationary in the field of
view without any manual adjustment of the R.A. slow-motion
control.
Understanding the Setting Circles
The setting circles on an equatorial mount enable you to
locate celestial objects by their “celestial coordinates”. Every
object resides in a specific location on the “celestial sphere”.
That location is denoted by two numbers: its right ascension
(R.A.) and declination (Dec.). In the same way, every location
on Earth can be described by its longitude and latitude. R.A.
is similar to longitude on Earth, and Dec. is similar to latitude.
The R.A. and Dec. values for celestial objects can be found
in any star atlas or star catalog.
The R.A. setting circle is scaled in hours, from 1 through 24,
with small marks in between representing 10-minute increments (there are 60 minutes in 1 hour of R.A.). The lower
set of numbers (closest to the plastic R.A. gear cover) apply
to viewing in the Northern Hemisphere, while the numbers
above them apply to viewing in the Southern Hemisphere.
The Dec. setting circle is scaled in degrees, with each mark
representing 1° increments. Values of Dec. coordinates
range from +90° to -90°. The 0° mark indicates the celestial
equator. When the telescope is pointed north of the celestial
equator, values of the Dec. setting circle are positive, and
when the telescope is pointed south of the celestial equator,
values of the Dec. setting circle are negative.
So, the coordinates for the Orion Nebula listed in a star atlas
will look like this:
R.A. 5h 35.4m Dec. -5° 27'
That’s 5 hours and 35.4 minutes in right ascension, and -5
degrees and 27 arc-minutes in declination (there are 60 arcminutes in 1 degree of declination).
Before you can use the setting circles to locate objects, the
mount must be well polar aligned, and the R.A. setting circle
must be calibrated. The Dec. setting circle has been permanently calibrated at the factory, and should read 90° whenever the telescope optical tube is parallel with the R.A. axis.
Calibrating the Right Ascension Setting Circle
1. Identify a bright star near the celestial equator (Dec. = 0°)
and look up its coordinates in a star atlas.
2. Loosen the R.A. and Dec. lock knobs on the equatorial
mount, so the telescope optical tube can move freely.
3. Point the telescope at the bright star near the celestial
equator whose coordinates you know. Lock the R.A. and
Dec. lock knobs. Center the star in the telescope’s field of
view with the slow-motion control cables.
4. Loosen the thumb screw located just above the R.A. setting circle pointer; this will allow the setting circle to rotate
freely. Rotate the setting circle until the pointer indicates
the R.A. coordinate listed in the star atlas for the object.
Retighten the thumb screw.
Finding Objects With the Setting Circles
Now that both setting circles are calibrated, look up in a star
atlas the coordinates of an object you wish to view.
1. Loosen the Dec. lock knob and rotate the telescope until
the Dec. value from the star atlas matches the reading on
the Dec. setting circle. Remember that values of the Dec.
setting circle are positive when the telescope is pointing
north of the celestial equator (Dec. = 0°), and negative
when the telescope is pointing south of the celestial
equator. Retighten the lock knob.
2. Loosen the R.A. lock knob and rotate the telescope until
the R.A. value from the star atlas matches the reading
on the R.A. setting circle. Remember to use the lower set
of numbers on the R.A. setting circle. Retighten the lock
knob.
Most setting circles are not accurate enough to put an object
dead-center in the telescope’s eyepiece, but they should
place the object somewhere within the field of view of the
finder scope, assuming the equatorial mount is accurately
polar aligned. Use the slow-motion controls to center the
object in the finder scope, and it should appear in the telescope’s field of view.
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Figure 6a.
illustrations, the mount and tripod remain stationary; only the R.A.
and Dec. axes are moved.
Telescope pointing south. Note that in all these
Figure 6b. Telescope pointing north.
Figure 6c. Telescope pointing east.
The R.A. setting circle must be re-calibrated every time you
wish to locate a new object. Do so by calibrating the setting
circle for the centered object before moving on to the next
one.
Confused About Pointing the Telescope?
Beginners occasionally experience some confusion about
how to point the telescope overhead or in other directions. In
Figure 1 the telescope is pointed north, as it would be during
polar alignment. The counterweight shaft is oriented downward. But it will not look like that when the telescope is pointed in other directions. Let’s say you want to view an object
that is directly overhead, at the zenith. How do you do it?
One thing you DO NOT do is make any adjustment to the
latitude adjustment T-bolt. That will nullify the mount’s polar
alignment. Remember, once the mount is polar aligned, the
telescope should be moved only on the R.A. and Dec. axes.
To point the scope overhead, first loosen the R.A. lock knob
Figure 6d. Telescope pointing west.
and rotate the telescope on the R.A. axis until the counterweight shaft is horizontal (parallel to the ground). Then
loosen the Dec. lock knob and rotate the telescope until it
is pointing straight overhead. The counterweight shaft is still
horizontal. Then retighten both lock knobs.
Similarly, to point the telescope directly south, the counterweight shaft should again be horizontal. Then you simply
rotate the scope on the Dec. axis until it points in the south
direction.
What if you need to aim the telescope directly north, but at
an object that is nearer to the horizon than Polaris? You can’t
do it with the counterweight down as pictured in Figure 1.
Again, you have to rotate the scope in R.A. so the counterweight shaft is positioned horizontally. Then rotate the scope
in Dec. so it points to where you want it near the horizon.
To point the telescope to the east or west, or in other directions, you rotate the telescope on its R.A. and Dec. axes.
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Depending on the altitude of the object you want to observe,
the counterweight shaft will be oriented somewhere between
vertical and horizontal.
Figure 6 illustrates how the telescope will look pointed at the
four cardinal directions—north, south, east, and west.
The key things to remember when pointing the telescope
are, first that you only move it in R.A. and Dec., not in azimuth or latitude (altitude), and second, the counterweight
and shaft will not always appear as it does in Figure 1. In
fact, it almost never will!
6. Using Your Telescope—
Astronomical Observing
Choosing an Observing Site
When selecting a location for observing, get as far away as
possible from direct artificial light such as streetlights, porch
lights, and automobile headlights. The glare from these lights
will greatly impair your dark-adapted night vision. Set up on
a grass or dirt surface, not asphalt, because asphalt radiates
more heat. Heat disturbs the surrounding air and degrades
the images seen through the telescope. Avoid viewing over
rooftops and chimneys, as they often have warm air currents
rising from them. Similarly, avoid observing from indoors
through an open (or closed) window, because the temperature difference between the indoor and outdoor air will cause
image blurring and distortion.
If at all possible, escape the light-polluted city sky and head
for darker country skies. You’ll be amazed at how many more
stars and deep-sky objects are visible in a dark sky!
Cooling the Telescope
All optical instruments need time to reach “thermal equilibrium.” The bigger the instrument and the larger the temperature change, the more time is needed. Allow at least a halfhour for your telescope to cool to the temperature outdoors.
In very cold climates (below freezing), it is essential to store
the telescope as cold as possible. If it has to adjust to more
than a 40° temperature change, allow at least one hour.
Beware, too, that nearby porch lights, streetlights, and car
headlights will ruin your night vision.
Aiming the Telescope
To view an object in the main telescope, first loosen both the
R.A. and Dec. lock knobs. Aim the telescope at the object
you wish to observe by “eyeballing” along the length of the
telescope tube (or use the setting circles to “dial in” the
object’s coordinates). Then look through the (aligned) finder
scope and move the telescope tube until the object is generally centered on the finder’s crosshairs. Retighten the R.A.
and Dec. lock knobs. Then accurately center the object on
the finder’s crosshairs using the R.A. and Dec. slow-motion
controls. The object should now be visible in the main telescope with a low-power (long focal length) eyepiece. If necessary, use the R.A. and Dec. slow-motion controls to reposition the object within the field of view of the main telescope’s
eyepiece.
Focusing the Telescope
Practice focusing the telescope in the daytime before using it
for the first time at night. Start by turning the focus knob until
the focuser drawtube is near the center of its adjustment
range. Insert the star diagonal into the focuser drawtube and
an eyepiece into the star diagonal (secure with the thumbscrews). Point the telescope at a distant subject and center it
in the field of view. Now, slowly rotate the focus knob until the
object comes into sharp focus. Go a little bit beyond sharp
focus until the image just starts to blur again, then reverse
the rotation of the knob, just to make sure you hit the exact
focus point. The telescope can only focus on objects at least
50 to 100 feet away.
Do You Wear Eyeglasses?
If you wear eyeglasses, you may be able to keep them on
while you observe, if your eyepieces have enough “eye relief”
to allow you to see the whole field of view. You can try this
by looking through the eyepiece first with your glasses on
and then with them off, and see if the glasses restrict the
view to only a portion of the full field. If they do, you can easily observe with your glasses off by just refocusing the telescope the needed amount.
Let Your Eyes Dark-Adapt
Don’t expect to go from a lighted house into the darkness
of the outdoors at night and immediately see faint nebulas,
galaxies, and star clusters—or even very many stars, for
that matter. Your eyes take about 30 minutes to reach perhaps 80% of their full dark-adapted sensitivity. As your eyes
become dark-adapted, more stars will glimmer into view and
you’ll be able to see fainter details in objects you view in your
telescope.
To see what you’re doing in the darkness, use a red-filtered
flashlight rather than a white light. Red light does not spoil
your eyes’ dark adaptation like white light does. A flashlight
with a red LED light is ideal, or you can cover the front of a
regular incandescent flashlight with red cellophane or paper.
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Calculating the Magnification
It is desirable to have a range of eyepieces of different focal
lengths, to allow viewing over a range of magnifications. To
calculate the magnification, or power, of a telescope, simply
divide the focal length of the telescope by the focal length of
the eyepiece (the number printed on the eyepiece):
Telescope F.L. ÷ Eyepiece F.L. = Magnification
For example, the AstroView 90 EQ, which has a focal length
of 910mm, used in combination with the suppled 25mm
Sirius Plössl eyepiece, yields a magnification of:
910 ÷ 25 = 36x
Every telescope has a useful magnification limit of about 2x
per millimenter of aperture. This comes to about 180x for the
AstroView 90. Claims of higher power by some telescope
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manufacturers are a misleading advertising gimmick and
should be dismissed. Keep in mind that at higher powers, an
image will always be dimmer and less sharp (this is a fundamental law of optics). The steadiness of the air (the “seeing”)
can also limit how much magnification an image can tolerate.
Always start viewing with your lowest-power (longest focal
length) eyepiece in the telescope. After you have located and
looked at the object with it, you can try switching to a higher
power eyepiece to ferret out more detail, if atmospheric conditions permit. If the image you see is not crisp and steady,
reduce the magnification by switching to a longer focal length
eyepiece. As a general rule, a small but well-resolved image
will show more detail and provide a more enjoyable view
than a dim and fuzzy, over-magnified image.
“Seeing” and Transparency
Atmospheric conditions vary significantly from night to night.
“Seeing” refers to the steadiness of the Earth’s atmosphere
at a given time. In conditions of poor seeing, atmospheric
turbulence causes objects viewed through the telescope to
“boil.” If the stars are twinkling noticeably when you look up
at the sky with just your eyes, the seeing is bad and you will
be limited to viewing with low powers (bad seeing affects
images at high powers more severely). Planetary observing
may also be poor.
In conditions of good seeing, star twinkling is minimal and
images appear steady in the eyepiece. Seeing is best overhead, worst at the horizon. Also, seeing generally gets better
after midnight, when much of the heat absorbed by the Earth
during the day has radiated off into space.
Avoid looking over buildings, pavement, or any other source
of heat, as they will cause “heat wave” disturbances that will
distort the image you see through the telescope.
Especially important for observing faint objects is good
“transparency”—air free of moisture, smoke, and dust. All
tend to scatter light, which reduces an object’s brightness.
Transparency is judged by the magnitude of the faintest stars
you can see with the unaided eye (6th magnitude or fainter is
desirable).
Rotating the Diagonal
When looking at objects in different areas of the night sky,
the eyepiece may become positioned so that is uncomfortable or impossible to look through. If the eyepiece is in an
undesirable position, the diagonal can be rotated in order to
provide a more comfortable viewing angle. First, loosen the
thumbscrew on the eyepiece adapter, but make sure to hold
the diagonal in place so that it won’t fall to the ground. Also,
secure the eyepiece in the diagonal so that it won’t fall out
when rotating the diagonal. Retighten the thumbscrew on the
eyepiece adapter once the diagonal has been rotated to an
appropriate position.
What to Expect
So what will you see with your telescope? You should be
able to see bands on Jupiter, the rings of Saturn, craters on
the Moon, the waxing and waning of Venus, and possibly
hundreds of deep sky objects. Do not expect to see color
as you do in NASA photos, since those are taken with longexposure cameras and have ‘false color’ added. Our eyes are
not sensitive enough to see color in deep-sky objects except
in a few of the brightest ones.
Remember that you are seeing these objects using your own
telescope with your own eyes! The object you see in your
eyepiece is in real-time, and not some conveniently provided
image from an expensive NASA probe. Each session with
your telescope will be a learning experience. Each time you
work with your telescope it will get easier to use, and objects
will become easier to find. Take it from us, there is big difference between looking at a well-made full-color NASA image
of a deep-sky object in a lit room during the daytime, and
seeing that same object in your telescope at night. One can
merely be a pretty image someone gave to you. The other is
an experience you will never forget!
A. The Moon
With its rocky, cratered surface, the Moon is one of the easiest and most interesting targets to view with your telescope.
The best time to observe our one and only natural satellite
is during a partial phase, that is, when the Moon is NOT full.
During partial phases, shadows on the surface reveal more
detail, especially right along the border between the dark
and light portions of the disk (called the “terminator”). A full
Moon is too bright and devoid of surface shadows to yield
a pleasing view. Try using a Moon Filter to dim the Moon
when it is very bright. It simply threads onto the bottom of the
eyepieces (you must first remove the eyepiece from the star
diagonal to attach the Moon filter).
B. The Sun
You can change your nighttime telescope into a daytime
Sun viewer by installing an optional full-aperture solar filter
over the front opening of the AstroView 90 EQ. The primary
attraction is sunspots, which change shape, appearance,
and location daily. Sunspots are directly related to magnetic
activity in the Sun. Many observers like to make drawings
of sunspots to monitor how the Sun is changing from day to
day.
Important Note: Do not look at the Sun with any optical
instrument without a professionally made solar filter, or
permanent eye damage could result. Leave the cover
caps on the finder scope, or better yet, remove the finder
scope from the telescope when solar viewing.
C. The Planets
The planets don’t stay put like the stars (they don’t have fixed
R.A. and Dec. coordinates), so you’ll have to refer to www.
telescope.com or to charts published monthly in Astronomy,
Sky & Telescope, or other astronomy magazines to locate
them. Venus, Mars, Jupiter, and Saturn are the brightest
objects in the sky after the Sun and the Moon. Not all four of
these planets are normally visible at any one time.
JUPITER The largest planet, Jupiter, is a great subject to
observe. You can see the disk of the giant planet and watch
the ever-changing positions of its four largest moons, Io,
Callisto, Europa, and Ganymede. If atmospheric conditions
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are good, you may be able to resolve thin cloud bands on the
planet’s disk.
SATURN The ringed planet is a breathtaking sight when it is
well positioned. The tilt angle of the rings varies over a period
of many years; sometimes they are seen edge-on, while at
other times they are broadside and look like giant “ears” on
each side of Saturn’s disk. A steady atmosphere (good seeing) is necessary for a good view. You may probably see a
tiny, bright “star” close by; that’s Saturn’s brightest moon,
Titan.
VENUS At its brightest, Venus is the most luminous object in
the sky, excluding the Sun and the Moon. It is so bright that
sometimes it is visible to the naked eye during full daylight!
Ironically, Venus appears as a thin crescent, not a full disk,
when at its peak brightness. Because it is so close to the
Sun, it never wanders too far from the morning or evening
horizon. No surface markings can be seen on Venus, which
is always shrouded in dense clouds.
MARS If atmospheric conditions are good, you may be able
to see some subtle surface detail on the Red Planet, possibly even the polar ice cap. Mars makes a close approach
to Earth every two years; during those approaches its disk is
larger and thus more favorable for viewing.
D. Stars
Stars will appear like twinkling points of light in the telescope.
Even powerful telescopes cannot magnify stars to appear
as more than points of light! You can, however, enjoy the different colors of the stars and locate many pretty double and
multiple stars. The famous “Double-Double” in the constellation Lyra and the gorgeous two-color double star Albireo in
Cygnus are favorites. Defocusing the image of a star slightly
can help bring out its color.
E. Deep-Sky Objects
Under dark skies, you can observe a wealth of fascinating
deep-sky objects, including gaseous nebulas, open and
globular star clusters, and different types of galaxies. Most
deep-sky objects are very faint, so it is important that you
find an observing site well away from light pollution. Take
plenty of time to let your eyes adjust to the darkness. Don’t
expect these subjects to appear like the photographs you
see in books and magazines; most will look like dim gray
smudges. (Our eyes are not sensitive enough to see color
in such faint objects.) But as you become more experienced
and your observing skills get sharper, you will be able to discern more subtle details.
Remember that the higher the magnification you use, the
dimmer the image will appear. So stick with low power when
observing deep-sky objects, because they’re already very
faint.
How to Find Interesting Celestial Objects—
Starhopping
Star hopping, as it is called by astronomers, is perhaps the
simplest way to hunt down deep-sky objects to view in the
night sky. It entails first pointing the telescope at a bright star
close to the object you wish to observe, and then progressing
Figure 7. Starhopping is a good way to locate hard-to-find
objects. Refer to a star chart to map a route to the object that uses
bright stars as guideposts. Center the first star you’ve chosen
in the finder scope and telescope eyepiece (1). Now move the
scope carefully in the direction of the next bright star (2), until it
is centered. Repeat (3 and 4). The last hop (5) should place the
desired object in the eyepiece.
to other stars closer and closer to the object until it is in the
field of view of the eyepiece. It is a very intuitive technique
that has been employed for hundreds of years by professional and amateur astronomers alike. Keep in mind, as with any
new task, that star hopping may seem challenging at first, but
will become easier over time and with practice.
To star hop, only a minimal amount of additional equipment
is necessary. A star chart or atlas that shows stars to at least
magnitude 5 is required. Select one that shows the positions
of many deep-sky objects, so you will have a lot of options to
choose from. If you do not know the positions of the constellations in the night sky, you will need a planisphere to identify
them.
Start by choosing bright objects to view. The brightness of
an object is measured by its visual magnitude; the brighter
an object, the lower its magnitude. Choose an object with
a visual magnitude of 9 or lower. Many beginners start with
the Messier objects, which represent some of the best and
brightest deep-sky objects, first catalogued about 200 years
ago by the French astronomer Charles Messier.
Determine in which constellation the object lies. Now, find the
constellation in the sky. If you do not recognize the constellations on sight, consult a planisphere. The planisphere gives
an all-sky view and shows which constellations are visible on
a given night at a given time.
Now, look at your star chart and find the brightest star in the
constellation that is near the object you are trying to find.
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Using the finder scope, point the telescope at this star and
center it on the crosshairs. Next, look again at the star chart
and find another suitably bright star near the bright star currently centered in the finder. Keep in mind that the field of
view of the finder scope is about 7°, so you should choose
another star that is no more that 7° from the first star, if possible. Move the telescope slightly, until the telescope is centered on the new star.
Continue using stars as guideposts in this way until you are
at the approximate position of the object you are trying to
find (Figure 7). Look in the telescope’s eyepiece, and the
object should be somewhere within the field of view. If it’s
not, sweep the telescope carefully around the immediate
vicinity until the object is found.
If you have trouble finding the object, start the star hop again
from the brightest star near the object you wish to view. This
time, be sure the stars indicated on the star chart are in fact
the stars you are centering in the eyepiece.
7. Astrophotography
Moon Photography
This is perhaps the simplest form of astrophotography, as no
motor drive is required. All that is needed is a T-ring for your
specific camera. Connect the T-ring to your camera body,
and remove the diagonal and eyepiece from the telescope’s
focuser. Then thread the camera and T-ring directly onto
the telescope’s focuser, coupling the telescope and camera
body.
Now you’re ready to shoot. Point the telescope toward the
Moon, and center it within the camera’s viewfinder. Focus
the image with the telescope’s focuser. Try several exposure
times, all less than 1 second, depending on the phase of
the Moon and the ISO (film speed) of the film being used. A
remote shutter release is recommended , since touching the
camera’s shutter release can vibrate the camera enough to
ruin the exposure.
This method of taking pictures is the same method with
which a daytime, terrestrial photograph could be taken
through the AstroView 90.
Planetary Photography
Once you’ve mastered basic Moon photography, you’re ready
to get images of the planets. This type of astrophotography
also may be used to capture highly magnified shots of the
Moon. In addition to the T-adapter already mentioned, a single-axis electronic drive and universal 1.25” camera adapter
are also required. The electronic drive is necessary because
of the longer exposure required for planetary photography.
The longer exposure time would cause the image to blur if
no motor drive were used for tracking. The equatorial mount
must be precisely polar aligned, too.
As before, connect the T-ring to your camera. Before connecting the universal camera adapter to the T-ring, an eyepiece
must be inserted and locked into the body of the adapter.
Start by using a medium-low power eyepiece (about 25mm);
you can increase the magnification later by using a higherpower eyepiece. Then connect the entire camera adapter,
with eyepiece inside, to the T-ring. Insert the whole system
into the telescope’s focuser drawtube and secure firmly with
the thumbscrew.
Aim the telescope at the planet (or Moon) you wish to shoot.
The image will be highly magnified, so you may need to use
the finder scope to center it within the camera’s viewfinder.
Turn the motor drive on. Adjust the telescope’s focuser so
that the image appears sharp. The camera’s shutter is now
ready to be opened. A remote shutter release must be used
or the image will be blurred beyond recognition! Try exposure
times between 1 and 10 seconds, depending on the brightness of the planet to be photographed and the ISO of the
film being used.
“Piggybacking” Photography
The Moon and planets are interesting targets for the budding astrophotographer, but what’s next? Literally thousands
of deep-sky objects can be captured on film with a type of
astrophotography called “piggybacking.” The basic idea is
that a camera with its own camera lens attached rides on
top of the main telescope. The telescope and camera both
move with the rotation of the Earth when the mount is polar
aligned and the motor drive is engaged. This allows for a
long exposure through the camera without blurring of the
object or background stars. In addition to the motor drive, an
illuminated reticle eyepiece is also needed. The T-ring and
camera adapter are not needed, since the camera is exposing through its own lens. Any camera lens with a focal length
between 50mm and 400mm is appropriate.
On the top of one of the tube rings is a piggyback camera
adapter. This is the black knob with the threaded shaft protruding through its center. The tube ring with the piggyback
adapter on it should be closest to the front of the telescope.
Remove the tube rings from the equatorial mount and swap
their positions, if necessary. Now, connect the camera to the
piggyback adapter. There should be a 1/4”-20 mounting hole
in the bottom of the camera’s body. Thread the protruding
shaft of the piggyback adapter into the 1/4”-20 hole in the
camera a few turns. Position the camera so that it is parallel
with the telescope tube and turn the knurled black knob of
the piggyback adapter counterclockwise until the camera is
locked into position.
Aim the telescope at a deep-sky object. It should be a fairly
large deep-sky object, as the camera lens will likely have a
wide field of view. Check to make sure that the object is also
centered in the camera’s viewfinder. Turn the motor drive
on. Now, look into the telescope’s eyepiece and center the
brightest star within the field of view. Remove the eyepiece
and insert the illuminated reticle eyepiece into the telescope’s
star diagonal. Turn the eyepiece’s illuminator on (dimly!).
Recenter the bright star (guide star) on the crosshairs of the
reticle eyepiece. Check again to make sure the object to be
photographed is still centered within the camera’s field of
view. If it is not, recenter it either by repositioning the camera
on the piggyback adapter, or by moving the main telescope.
If you move the main telescope, then you will need to recen-
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ter another guide star on the eyepiece’s crosshairs. Once the
object is centered in the camera, and a guide star is centered
in the eyepiece, you’re ready to shoot.
Deep-sky objects are quite faint, and typically require exposures on the order of 10 minutes. To hold the camera’s shutter open this long, you will need a locking shutter release
cable . You will also need to set the camera’s shutter to the
“B” (bulb) setting for the locking shutter release to work
properly. Depress the release cable and lock it. You are now
exposing your first deep-sky object.
While exposing through the camera lens, you will need to
monitor the accuracy of the mount’s tracking by looking
through the illuminated reticle eyepiece in the main telescope. If the guide star drifts from its initial position, then use
the hand controller of the motor drive to “bump” the guide
star back to the center of the crosshairs. The hand controller only moves the telescope along the R.A. axis, which is
where most of the corrections will be made. If the guide star
appears to be drifting significantly along the Dec. axis, then
the mount’s slow-motion control cables can be carefully used
to move the guide star back onto the crosshairs. Any drifting
along the Dec. axis is due to imprecise polar alignment. If the
drifting is significant, you may need to polar align the mount
more accurately.
When the exposure is complete, unlock the shutter release
cable and close the camera’s shutter.
Astrophotography can be enjoyable and rewarding, as well
as frustrating and time-consuming. Start slowly and consult
outside resources, such as books and magazines, for more
details about astrophotography. Remember . . . have fun!
8. Terrestrial Viewing
The AstroView 90 may also be used for long-distance viewing over land. For this application we recommend substitution of an Orion 45° Correct-Image Diagonal for the 90° star
diagonal that comes standard with the telescope. The correct-image diagonal will yield an upright, non-reversed image
and also provides a more comfortable viewing angle, since
the telescope will be aimed more horizontally for terrestrial
subjects.
For terrestrial viewing, it’s best to stick with low powers of
50x or less. At higher powers the image loses sharpness and
clarity. That’s because when the scope is pointed near the
horizon, it is peering through the thickest and most turbulent
part of the Earth’s atmosphere.
Remember to aim well clear of the Sun, unless the front of
the telescope is fitted with a professionally made solar filter
and the finder scope is covered with foil or some other completely opaque material.
9. Care and Maintenance
If you give your telescope reasonable care, it will last a
lifetime. Store it in a clean, dry, dust-free place, safe from
rapid changes in temperature and humidity. Do not store the
telescope outdoors, although storage in a garage or shed is
OK. Small components like eyepieces and other accessories
should be kept in a protective box or storage case. Keep the
cap on the front of the telescope when it is not in use.
Cleaning the Tube
Your AstroView 90 telescope requires very little mechanical
maintenance. The optical tube is aluminum and has a smooth
painted finish that is fairly scratch-resistant. If a scratch does
appear on the tube, it will not harm the telescope. If you
wish, you may apply some auto touch-up paint to the scratch.
Smudges on the tube can be wiped off with a soft cloth and a
household cleaner such as Windex or Formula 409.
Cleaning Lenses
Any quality optical lens cleaning tissue and optical lens
cleaning fluid specifically designed for multi-coated optics
can be used to clean the AstroView’s objective lens or the
exposed lenses of your eyepieces or finder scope. Never
use regular glass cleaner or cleaning fluid designed for eyeglasses. Before cleaning with fluid and tissue, blow any loose
particles off the lens with a blower bulb or compressed air.
Then apply some cleaning fluid to a tissue, never directly
on the optics. Wipe the lens gently in a circular motion, then
remove any excess fluid with a fresh lens tissue. Oily fingerprints and smudges may be removed using this method.
Use caution; rubbing too hard may scratch the lens. For the
large surface of the objective lens, clean only a small area at
a time, using a fresh lens tissue on each area. Never reuse
tissues.
10. Specifications
Optical tube: Seamless aluminum
Objective lens: Achromatic doublet, air spaced, optical glass
elements
Objective lens coatings: Fully coated with multi-coatings
Objective lens diameter: 90mm (3.5")
Focal length: 910mm
Focal ratio: f/10
Eyepieces: 25mm and 10mm Sirius Plössls, fully coated with
multi-coatings, 1.25"
Magnification: 36x (with 25mm), 91x (with 10mm)
Focuser: Rack and pinion
Diagonal: 90° Star diagonal, mirror type, 1.25"
Finder scope: 6x Magnification, 30mm aperture, achromatic,
crosshairs
Mount: EQ-2 German-type equatorial
Tripod: Aluminum
Motor drive: Optional
Weight: 24 lbs.
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One-Year Limited Warranty
This Orion AstroView 90 EQ is warranted against defects in materials or workmanship for a
period of one year from the date of purchase. This warranty is for the benefit of the original
retail purchaser only. During this warranty period Orion Telescopes & Binoculars will repair or
replace, at Orion’s option, any warranted instrument that proves to be defective, provided it
is returned postage paid to: Orion Warranty Repair, 89 Hangar Way, Watsonville, CA 95076.
If the product is not registered, proof of purchase (such as a copy of the original invoice) is
required.
This warranty does not apply if, in Orion’s judgment, the instrument has been abused, mishandled, or modified, nor does it apply to normal wear and tear. This warranty gives you specific legal rights, and you may also have other rights, which vary from state to state. For further
warranty service information, contact: Customer Service Department, Orion Telescopes &
Binoculars, P. O. Box 1815, Santa Cruz, CA 95061; (800) 676-1343.
Orion Telescopes & Binoculars
Post Office Box 1815, Santa Cruz, CA 95061
Customer Support Help Line (800) 676-1343 • Day or Evening
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