Orion ATLAS EQ-G User manual

INSTRUCTION MANUAL
IN 279 Rev. D 06/13
Providing Exceptional Consumer Optical Products Since 1975
Customer Support (800)-676-1343
E-mail: [email protected]
Corporate Offices (831)‑763‑7000
89 Hangar Way, Watsonville, CA 95076
Orion Atlas™EQ-G
Equatorial Mount
#24338

2
Figure 1. The Atlas EQ‑G mount.
Power switch
Power indicator light
12V DC power jack
Auto guider jack
Right Ascension
setting circle
Right Ascension
lock lever
Hand controller jack
Latitude scale
Latitude adjustment L‑bolts
Center support shaft
Tripod center support tray
GoTo hand controller
Tube ring mounting plate
Mounting plate lock knobs
Declination lock lever
Declination setting circle
Front opening
Counterweight shaft lock lever
Counterweight shaft
Counterweights
Counterweight lock knobs
“Toe‑saver”
GoTo hand controller cable
Tripod leg
Leg lock levers

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Table of Contents
1. Unpacking............................ 3
2. Parts List............................. 3
3. Assembly ............................ 3
4. Attaching a Telescope................... 4
5. Balancing a Telescope .................. 5
6. Setting Up and Using the Equatorial Mount . . 5
7. The SynScan GoTo Hand Controller........ 8
8. Technical Specifications ................. 8
Appendix: Enhancing the Pointing Accuracy ... 9
1. Unpacking
The entire mount will arrive in three boxes, one containing
the tripod, one containing the equatorial mount, and one con‑
taining the hand controller. Be careful unpacking the boxes.
We recommend keeping the boxes and original packaging.
In the event that the mount needs to be shipped to another
location, or returned to Orion for warranty repair, having the
proper packaging will ensure that your mount will survive the
journey intact.
Make sure all the parts in the Parts List are present. Be
sure to check the box carefully, as some parts are small.
If anything appears to be missing or broken, immediate‑
ly call Orion Customer Support (800‑676‑1343) or email
suppor[email protected] for assistance.
2. Parts List
Box 1: Tripod
Qty. Item
1 Tripod
2 Counterweights (11lbs. each)
1 Tripod center support tray
Box 2: Equatorial Mount
1 Equatorial mount
1 Tube ring mounting plate
1 12V DC Power cable
1 SynScan GoTo hand controller
1 GoTo hand controller cable
1 GoTo hand controller bracket
1 Computer interface cable (RS‑232)
1 Wire clip
3. Assembly
Refer to Figure 1 as needed during the assembly process.
1. Stand the tripod legs upright and spread the legs out as
far as they will go. Make certain that the leg lock levers
are tightened. Keep the tripod legs at their shortest (fully
retracted) length, for now; you can extend them to a more
desirable length later, after the mount is fully assembled.
2. Place the base of the equatorial mount onto the tripod
head. Orient the equatorial mount so that the post on the
tripod head lines up with the azimuth adjustment knobs on
the equatorial mount (Figure 2). You may need to loosen
the azimuth adjustment knobs on the equatorial mount in
order to fit the mount onto the tripod head.
3. Thread the center support shaft up through the tripod
head and into the bottom of the equatorial mount until
tight. Use the upper knob on the center support shaft to do
Congratulations on your purchase of a quality Orion mount. Your new Atlas EQ‑G mount works with many different
optical tubes. Designed for astronomical use, the Atlas EQ‑G provides a solid, stable foundation for precise navigation of the
night sky. The internally housed, dual‑axis stepper motors provide smooth slewing and tracking of any celestial object. With a
little practice, you’ll find that the Atlas EQ‑G mount is an invaluable tool for getting the most out of your astronomical observing
sessions.
These instructions will help you set up and properly use your equatorial mount. Please read them over thoroughly before getting
started.
Figure 2. Orient the equatorial head so that the post on the tripod
lines up with the azimuth adjustment knobs on the equatorial mount.
Azimuth
adjustment
knobs
Post
WARNING: Never look directly at the Sun through your
telescope or its finder scope – even for an instant – with-
out a professionally made solar filter that completely cov-
ers the front of the instrument, or permanent eye damage
could result. Young children should use this telescope
only with adult supervision.

4
this. The equatorial mount should now be firmly connected
to the tripod.
4. Remove the knob and washer from the bottom of the
center support shaft. Slide the tripod support tray up the
bottom of the central support shaft until the three tray
arms are touching the legs of the tripod. The flat side of
the support tray should be facing up. Make sure the “V” of
each tray arm is against a tripod leg. Place the washer on
the center support shaft against the tray, and follow it by
threading the knob all the way up the center support shaft
until it is tight against the tray. The tripod support tray pro‑
vides additional stability for the tripod, and holds up to five
1.25" eyepieces and two 2" eyepieces.
5. Loosen the counterweight shaft lock lever and fully extend
the counterweight shaft. Retighten the lock lever.
6. Remove the knurled “toe saver” retaining screw on the
bottom of the counterweight shaft and slide both counter‑
weights onto the shaft. Make sure the counterweight lock
knobs are adequately loosened to allow the counterweight
shaft to pass through the hole. Position the counterweights
about halfway up the shaft and tighten the lock knobs.
Replace the toe saver at the end of the bar. The toe saver
prevents the counterweights from falling on your foot if the
lock knobs happen to come loose.
Your Atlas EQ‑G mount is now fully assembled and should
resemble Figure 1 except for the hand controller, which is cov‑
ered in the separate SynScan GoTo Hand Controller manual.
4. Attaching a Telescope
The Atlas EQ‑G equatorial mount is designed to hold telescope
tubes weighing up to approximately 40 lbs. For heavier tele‑
scopes, the mount may not provide sufficient stability for steady
imaging. Any type of telescope can be mounted on the Atlas
EQ‑G, including refractors, Newtonian reflectors, and catadio‑
tropics, provided a set of tube rings is available to couple the
tube to the mount. Orion sells a variety of telescope tube rings.
Please visit our website at OrionTelescopes.com for details.
1. Attach the tube mounting rings to the tube ring mounting
plate using the screws that come with the tube rings. The
screws should go through the center holes in the ends of
the mounting plate and rethread into the tube rings. Note
that the side of the mounting plate with the central “groove”
will be facing up (Figure 3). Use a small wrench to secure
the tube rings to the mounting plate.
Note: The tube ring mounting plate included with the Atlas
EQ‑G includes four optical axis offset adjustment screws;
these are the socket head cap screws located at each cor‑
ner of the mounting plate. These adjustment screws will be
explained further in Appendix A. For now, confirm that all four
adjustment screws are sufficiently unthreaded so that the
ends of their threaded shafts are flush with the top surface of
the tube ring mounting plate.
Note: The optical axis offset adjustment screws should be
oriented so that the threaded shaft extends upward through
the top surface of the tube ring mounting plate. If the tube
ring mounting plate arrives with the optical axis offset screws
installed backwards, reverse their orientation before proceed‑
ing (Figure 3).
2. Loosen the black mounting plate lock knobs on the top of
the equatorial mount. Place the mounting plate, with the
tube rings attached, in the slot on top of the equatorial
Figure 4. Proper operation of the equatorial mount requires
that the telescope tube be balanced on the R.A. and Dec. axes. (a)
With the R.A. lock lever released, slide the counterweights down
the counterweight shaft until they just counterbalance the telescope
tube. (b) When you let go with both hands, the tube should not drift
up or down. (c) With the Dec. lock lever released, loosen the tube
ring lock clamps a few turns and slide the telescope forward or back
in the tube rings. (d) When the tube is balanced about the Dec. axis,
it will not move when you let go.
a. b.
c. d.
Figure 3. The tube ring mounting plate.
Optical axis offset
adjustment screws
Flat washer
Lock washer
Tube ring
attachment screw

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mount. Position the mounting plate so that it is centered in
the slot. Re‑tighten the mounting plate lock knobs until the
plate is secure.
3. Open the tube rings and lay the telescope optical tube in
the rings at about the midpoint of the tube’s length. Rotate
the tube so that the focuser is at a convenient height for
viewing. Close the tube rings and tighten them.
Note: The Atlas EQ‑G mount is very heavy. Alone it weighs 54
lbs. With a large optical tube and counterweights it can easily
weigh over 100 lbs. Keep this in mind when moving the tele‑
scope even small distances, and use assistance when need‑
ed. It is best to remove the optical tube and counterweights
when moving the mount.
Note: Some telescope optical tubes (specifically Schmidt‑
Cassegrains and Maksutov‑Cassegrains) have a mounting
plate connected directly to the tube. For these telescopes,
optional tube rings are not required. Simply follow step 2
(above) to connect the telescope to the mount.
5. Balancing a Telescope
To ensure smooth movement of a telescope on both axes of
the equatorial mount, it is imperative that the optical tube is
properly balanced. We will first balance the telescope with
respect to the right ascension (R.A.) axis, then the declination
(Dec.) axis.
1. Keeping one hand on the telescope optical tube, loosen
the R.A. lock lever. Make sure the Dec. lock lever is locked,
for now. The telescope should now be able to rotate freely
about the right ascension axis. Rotate it until the counter‑
weight shaft is parallel to the ground (i.e., horizontal).
2. Now loosen both counterweight lock knobs and slide the
weights along the shaft until they exactly counterbalance
the telescope (Figure 4a). That’s the point at which the
shaft remains horizontal even when you let go with both
hands (Figure 4b). If the telescope refuses to balance
than you have either too much or too little counterweight.
Remove a counterweight, or add optional counterweights
if needed.
3. Retighten the counterweight lock knobs. The telescope is
now balanced on the right ascension axis.
4. To balance the telescope on the declination axis, first tight‑
en the R.A. lock lever, with the counterweight shaft still in
the horizontal position.
5. With one hand on the telescope optical tube, loosen the
Dec. lock lever. The telescope should now be able to rotate
freely about the declination axis.
6. Loosen the knurled ring clamps on the tube rings 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 4c).
7. Position the telescope in the tube rings so it remains hori‑
zontal when you carefully let go with both hands. This is
the balance point for the optical tube with respect to the
Dec. axis (Figure 4d).
8. Retighten the knurled ring clamps.
The telescope is now balanced on both axes. When you loos‑
en the lock lever on one or both axes and manually point the
telescope, it should move without resistance and should not
drift from where you point it.
6. 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 5) is designed to
compensate for that motion, allowing you to easily “track” the
movement of astronomical objects, thereby keeping them
from drifting out of your telescope’s field of view while you’re
observing.
This is accomplished by slowly rotating the telescope on its
right ascension (R.A.) axis, using the built in motor drive. 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 align‑
ment is achieved by pointing the mount’s right ascension axis
at the North Star, or Polaris. It lies within 1° of the north celes‑
tial pole (NCP), which is an extension of the Earth’s rotational
axis out into space. Stars in the Northern Hemisphere appear
to revolve around the NCP.
Figure 5. The Atlas EQ‑G mount.
Dec. lock lever
(not shown)
Front opening
R.A. lock lever
Polar axis
finder scope
Latitude scale
Latitude
adjustment L‑bolts
Azimuth
adjustment
knobs (2)
Declination (Dec) axis
Right Ascension
(R.A.) axis

6
To find Polaris in the sky, look north and locate the pattern
of the Big Dipper (Figure 6). 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° from the SCP, but it is barely
visible with the naked eye (magnitude 5.5).
For general visual observation, an approximate polar align‑
ment is sufficient.
1. Level the equatorial mount by adjusting the length of the
three tripod legs.
2. There are two latitude adjustment L‑bolts (see Figure 5);
loosen one while tightening the other. By doing this you
will adjust the latitude of the mount. Continue adjusting the
mount until the pointer on the latitude scale is set at the
latitude of your observing site. If you don’t know your lati‑
tude, consult a geographical atlas to find it. For example,
if your latitude is 35° North, set the pointer to 35. The lati‑
tude setting should not have to be adjusted again unless
you move to a different viewing location some distance
away.
3. Loosen the Dec. lock lever and rotate the telescope’s opti‑
cal tube until it is parallel with the right ascension axis, as
it is in Figure 5.
4. Move the tripod so the telescope tube and right ascen‑
sion axis point roughly at Polaris. If you cannot see Polaris
directly from your observing site, consult a compass and
rotate the tripod so the telescope points north.
The equatorial mount is now polar aligned for casual observ‑
ing. More precise polar alignment is recommended for
astrophotography. For this we recommend using the polar
axis finder scope.
From this point on in your observing session, you should not
make any further adjustments to 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.
The Polar Axis Finder Scope
The Atlas EQ‑G mount comes with a polar axis finder scope
(Figure 7) housed inside the right ascension axis of the
mount. When properly aligned and used, it makes accurate
polar alignment quick and easy to do. Unthread the cover at
the rear of the mount’s right ascension axis and remove the
cap on the front opening of the equatorial mount (Figure 5) to
view through the polar axis finder scope.
Alignment of the Polar Axis Finder Scope
1. Loosen the Dec. lock lever and rotate the optical tube
about the declination axis until you have a clear view
through the polar axis finder scope (Figure 8). Tighten the
Dec. lock lever.
2. Look through the polar finder at a distant object (during
the day) and center it in the crosshairs. You may need to
adjust the latitude adjustment L‑bolts and the tripod posi‑
tion to do this. Focus the polar finder by rotating the eye‑
piece.
3. Rotate the mount 180° about the R.A. axis. It may be con‑
venient to remove the counterweights and optical tube
before doing this.
4. Look through the polar finder again. Is the object being
viewed still centered on the crosshairs? If it is, then no
further adjustment is necessary. If not, then look through
the polar finder while rotating the mount about the R.A.
axis. You will notice that the object you have previously
centered moves in a circular path. Use the three alignment
set‑screws on the polar axis finder (Figure 7) to redirect
the crosshairs of the polar finder to the apparent center of
this circular path.
5. Repeat this procedure until the position that the crosshairs
point to does not rotate off‑center when the mount is rotat‑
ed in R.A.
The polar axis finder scope is now ready to be used. When
not in use, replace the plastic protective cover to prevent the
polar finder from getting bumped.
Using the Polar Axis Finder Scope
The reticle of the polar axis finder scope for the Atlas EQ‑G
has a tiny star map printed on it that makes precise polar
Figure 7. The polar axis finder scope.
Eyepiece
focus ring
Alignment
setscrew (3)
Focus
lock ring
Objective
lens
Figure 6. 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).
Big Dipper
(in Ursa Major)
Little Dipper
(in Ursa Minor)
Cassiopeia
N.C.P.
Pointer
Stars
Polaris

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alignment quick and easy. To polar align the mount using the
polar axis finder scope, follow these instructions:
1. Approximately polar‑align the mount as outlined in the
procedure above.
2. Loosen the Dec. lock lever and rotate the optical tube on
the declination axis so the tube is at a 90° angle to the right
ascension axis (Figure 8). Tighten the Dec. lock lever.
3. Focus the polar finder by rotating the eyepiece. Now, sight
Polaris in the polar axis finder scope. If you have followed
the approximate polar alignment procedure accurately,
Polaris will probably be within the field of view. If not, move
the tripod left‑to‑right, and adjust the latitude up‑and down
until Polaris is somewhere within the field of view of the
polar axis finder scope.
4. The mount has a built‑in illuminator that allows you to see
the reticle pattern in the polar axis finder scope at night.
Simply turn on the power switch on the Atlas EQ‑G mount
(see “Powering the Atlas EQ‑G Mount”) and the polar axis
finder scope reticle will be illuminated. Note the constel‑
lation Cassiopeia and the Big Dipper in the reticle. They
do not appear in scale, but they indicate the general posi‑
tions of Cassiopeia and the Big Dipper relative to the north
celestial pole (which is indicated by the cross at the cen‑
ter of the reticle). Rotate the reticle so the constellations
depicted match their current orientation in the sky when
viewed with the naked eye. To do this, release the R.A.
lock lever and rotate the main telescope around the R.A.
axis until the reticle is oriented with sky. For larger optical
tubes, you may need to remove the tube from the mount
to prevent it from bumping into the mount. Once the reticle
is correctly oriented, use the right ascension lock lever to
secure the mount’s position.
5. Now use the azimuth adjustment knobs (Figure 2) and
the latitude adjustment L‑bolts (Figure 5) on the mount
to position the star Polaris inside the tiny circle marked
“Polaris” on the finder’s reticle. You must first loosen the
knob underneath the equatorial mount on the center sup‑
port shaft to use the azimuth adjustment knobs. Once
Polaris is properly positioned within the reticle, you are
precisely polar aligned. Retighten the knob underneath
the equatorial mount.
If you do not have a clear view of Polaris from your observing
site, you will not be able to use the polar‑axis finder to pre‑
cisely polar align the telescope.
Note: From this point on in your observing session, you should
not make any further adjustments in the azimuth or the lati‑
tude of the mount, nor should you move the tripod. Doing so
will undo the polar alignment. The telescope should be moved
only about its right ascension and declination axes.
Additional Note Regarding Focusing the Polar
Axis Finder Scope
The polar axis finder scope is normally focused by simple
rotation of the eyepiece focus ring. However, if after adjust‑
ing the focus ring you find that the image of the reticle is
sharp, but the stars are out of focus, then you must adjust the
focus of the polar axis finder’s objective lens. To do this, first
remove the polar axis finder from the mount by unthreading
it. Look through the polar axis finder at a star (at night) or
distant object at least 1/4 mile away (during daylight). Use the
eyepiece focus ring to bring the reticle into sharp focus. Now,
loosen the focus lock ring (Figure 7) and thread the entire
objective end of the finder inward or outward until images
appear sharp. Re‑tighten the focus lock ring. Once the polar
axis finder’s objective lens is focused, it should not need to be
adjusted again.
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 down‑
ward. 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?
DO NOT make any adjustment to the latitude adjust‑
ment L‑bolts. That will spoil 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 lever and rotate
the telescope on the right ascension axis until the counter‑
weight shaft is horizontal (parallel to the ground). Then loosen
the Dec. lock lever and rotate the telescope until it is pointing
straight overhead. The counterweight shaft is still horizontal.
Then retighten both lock levers.
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 counterweights down as pictured in Figure 1.
Again, you have to rotate the scope in right ascension so that
the counterweight shaft is positioned horizontally. Then rotate
the scope in declination so it points to where you want it near
the horizon.
To point the telescope directly south, the counterweight shaft
should again be horizontal. Then you simply rotate the scope
on the declination axis until it points in the south direction.
Figure 8. The optical tube must be rotated about the declination
axis in order to view through the polar axis finder.

8
To point the telescope to the east or west, or in other direc‑
tions, you rotate the telescope on its right ascension and
declination axes. Depending on the altitude of the object you
want to observe, the counterweight shaft will be oriented
somewhere between vertical and horizontal.
Figure 9 illustrates how the telescope will look when point‑
ed at the four cardinal directions: north (Figure 9a), south
(Figure 9b), east (Figure 9c) and west (Figure 9d).
The key things to remember when pointing the telescope are
that a) you only move it in right ascension and declination, not
in azimuth or latitude (altitude), and b) the counterweight and
shaft will not always appear as it does in Figure 1. In fact it
almost never will!
Powering the Atlas EQ-G Mount
The Atlas EQ‑G should be powered by an 11V to 15V DC
power supply (tip positive) capable of producing continuous
current of a minimum 2 amps. We recommend using a porta‑
ble rechargeable battery, like the Dynamo Pro available from
Orion.
If you are using a field battery like the Orion Dynamo Pro, use
the 12V DC power cable supplied with your mount (male ciga‑
rette lighter plug on one end, standard 12V DC power plug
on other end) to connect the battery to the 12V DC power
jack on the mount. Make sure the Dynamo’s power switch is
in the “on” position after connecting. Then, to turn the mount
(and GoTo hand controller) on, simply press the switch on the
mount so it is in the “on” position.
Note: The power indicator LED on the mount (near the power
switch) will begin to flash when the battery power is low. When
the battery power is extremely low, the LED will flash rapidly.
Recharge or replace the battery as needed.
7. The SynScan GoTo
Hand Controller
The Atlas EQ‑G mount equipped with the GoTo hand control‑
ler provides easy, computerized location of thousands of night
sky objects such as planets, nebulae, star clusters, galaxies,
and more for viewing through your telescope. The SynScan
GoTo Hand Controller and internal dual‑axis motors allow you
to automatically point your telescope at a specific object, or
tour the skies with pushbutton simplicity. The user‑friendly
menu allows automatic slewing to over 42,000 objects. Even
inexperienced astronomers will find themselves quickly mas‑
tering the variety of features the GoTo hand controller offers in
just a few observing sessions.
For detailed information about the SynScan GoTo Hand
Controller, see the manual for the SynScan.
8. Technical Specifications
Mount: German equatorial
Tripod: Steel
Weight: 54 lbs.
Counterweights: Quantity 2, 11 lbs. each
Polar axis latitude adjustment: 10° to 65°
Polar axis finder scope: Included, illuminator built
into mount
Motor drives: Dual‑axis, GoTo comput‑
erized, internally housed
Operation: Northern or Southern
hemisphere
Power requirement: 12V DC, 2A (tip positive)
Motor type and resolution: Microstep driven 1.8°
stepper motors
Resolution: 0.144 arc sec (or
9,024,000 steps/rev)
Gear ratio: 705
This device complies with Part 15 of the FCC Rules. Operation
is subject to the following two conditions: (1) this device nay
not cause harmful interference, and (2) this device must
accept any interference received, including interference that
may cause undesired operation.
Changes of modifications not expressly approved by the party
responsible for compliance could void the user’s authority to
operate the equipment.
Note: This equipment has been tested and found to comply
with the limits for a Class B digital device, pursuant to Part
15 of the FCC Rules. These limits are designed to provide
reasonable protection against harmful interference in a resi‑
dential installation. This equipment generates, uses and can
radiate radio frequency energy and, if not installed and used
Figure 9. These illustrations show the telescope pointed in the four cardinal directions. (a) north, (b) south, (c) east, (d) west. Note that the
tripod and mount have not been moved; only the telescope has been moved on the its R.A. and Dec. axes.
a. b. c. d.

9
in accordance with the instructions, may cause harmful inter‑
ference to radio communications. However, there is no guar‑
antee that interference will no occur in a particular installation.
If this equipment does cause harmful interference to radio or
television reception, which can be determined by turning the
equipment off and on, the user is encouraged to try to correct
the interference by one or more of the following measures:
‑Reorient or relocate the receiving antenna.
‑Increase the separation between the equipment and
receiver.
‑Connect the equipment into an output on a circuit different
from that to which the receiver in connected.
‑Consult the dealer or an experienced radio/TV technician
for help.
A shielded cable must be used when connecting a peripheral
to the serial ports.
Appendix: Enhancing the
Pointing Accuracy
The Atlas EQ‑G produces pointing accuracy and tracking
accuracy adequate for most applications. If higher precision is
required, “cone” error calibration may be necessary.
Cone Error Calibration
“Cone” error is a common inaccuracy found on all German
equatorial mount designs. Cone error results from the optical
axis of the telescope not being aligned to the R.A. axis of the
mount. This affects the pointing accuracy of the Atlas EQ‑G.
Three‑star alignment automatically compensates for some
of the cone error, but pointing accuracy will be optimized by
mechanically minimizing the cone error. The following cali‑
bration procedure should be performed before the initial use
of the telescope and periodically thereafter to ensure peak
accuracy.
Testing for Cone Error
This test is performed at night using two bright stars located
on opposite hemispheres of the night sky. Confirm that the
telescope is properly polar‑aligned using the polar axis finder
scope. Perform the one‑star alignment using an eastern star
as the alignment star (see “One‑Star Alignment”). After com‑
pleting the star alignment, choose a bright star in the western
sky from the Atlas EQ‑G object database and press ENTER
to slew the telescope to the star. If the optical axis is perfectly
aligned to the R.A. axis, the telescope will accurately put the
star in the center of the eyepiece. This shows that there is no
cone error in your telescope setup and you will not need to
perform the calibration. It is acceptable if the star is slightly
off‑center as long as it appears in the eyepiece field of view
and reasonable close to the center. Many factors determine
the pointing accuracy of the Atlas EQ‑G. Incorrect star align‑
ment, loose R.A. or Dec. lock‑knobs, or cone error. If the Atlas
EQ‑G puts the star outside the eyepiece field of view, you
need to determine which of these factors is causing the point‑
ing inaccuracy. To determine if the inaccuracy is caused by
cone error, simply move the telescope about the R.A. axis by
pressing the Left or Right direction button. If the star can be
moved into the eyepiece field of view without adjusting the
Dec. axis, it is likely that cone error exists in your telescope
setup.
Calibration Procedure
1. Insert an illuminated reticle eyepiece (not supplied) into
the focuser (or diagonal) of the telescope. Confirm the
telescope is properly set up and balanced, and the finder‑
scope is aligned with the optical tube of the telescope.
Note: Steps 2 to 4 are to identify R.A. and DEC movements in
the reticle eyepiece. If you are already familiar with the move‑
ments, proceed to step 5.
2. Find a bright star and position the telescope so the star is
centered in the eyepiece field of view.
3. Look into the eyepiece. Move the telescope about the R.A.
axis using the R.A. direction buttons on the hand controller
while carefully observing the movement of the star.
4. Keep moving the telescope about the R.A. axis back and
forth to keep the star within the eyepiece field of view.
Rotate the eyepiece in the focuser (or diagonal) until the
Figure 10. Aligning the R.A. motion of the star with the crosshairs. Figure 11. Adjust the telescope in Dec. (with the hand controller)
to place the star on the R.A. crosshair.
.

10
movement of the star becomes parallel to one of the illu‑
minated crosshairs (Figure 10). This crosshair will repre‑
sent R.A. movement in the course of this procedure, and
the perpendicular crosshair will represent Dec. movement.
Tighten the set screws to secure the eyepiece in position.
Make sure the eyepiece will remain stationary while the
telescope is moved.
5. Point the telescope North and set the latitude scale to
your local latitude using the altitude adjustment L‑bolts.
Alternatively, place Polaris in the polar axis finder scope if
your polar axis finder scope is accurately aligned with the
mount.
6. Loosen the R.A. lock knob and rotate the telescope about
the R.A. axis until the counterweight shaft is parallel to the
ground (as shown in Figure 12a).
7. Using the Dec. direction button on the hand controller,
adjust the telescope in Dec. so Polaris lies on the R.A.
crosshairs of the illuminated reticle eyepiece (Figure 11).
8. Without moving the R.A. axis, adjust the azimuth adjust‑
ment knobs (Figure 2) to orient Polaris in the center of the
eyepiece field of view. Adjustment in Dec. axis using the
hand controller may be necessary.
9. Loosen the R.A. lock knob and carefully rotate the tele‑
scope 180° about the R.A. axis (Figure 12) This should
be done as accurately as possible referencing the R.A.
mechanical setting circle.
10.Adjust the position of the telescope in the Dec. axis so
Polaris lies on the R.A. crosshairs of the illuminated reticle
eyepiece.
11.Carefully push the telescope in horizontal motion while
observing the movement of Polaris in the eyepiece field of
view (Figure 13). This will determine which direction (left
or right) moves Polaris closer to the center of the eyepiece
field of view.
12.Carefully and gently loosen both the tube ring attachment
screws (Figure 3) by a couple of turns.
13.Make adjustments to the optical axis offset adjustment
screws (the socket head cap screws located at each
corner of the mounting plate (Figure 3) according to the
Figure 12. Rotate the telescope 180° about the R.A.axis.
a. b.

11
results of step 11. If Polaris moves toward the center when
the telescope is pushed as indicated in Figure 13, loos‑
en the adjustment screws near the front of the tube and
tighten the adjustment screws closer to the back of the
tube (Figure 14). If Polaris moves away from the center
when the telescope is pushed as in Figure 13, loosen the
adjustment screws near the back of the tube and tight‑
en the adjustment screws closer to the front of the tube
(Figure 14). Look into the eyepiece. Adjust the adjust‑
ment screws just enough to place Polaris HALF the dis‑
tance back to the center of the illuminated reticle eyepiece
(Figure 15).
14.Repeat these steps until Polaris remains in the center of
the eyepiece field of view, or moves slightly around the
center, when the mount is rotated about the R.A. axis.
Note: This calibration method can be applied to both refract‑
ing and reflecting telescope designs. Differences in the optical
path of telescopes do not affect how the telescope tube and
tube rings should be adjusted on the mounting plate.
Figure 15. Using the optical axis offset screws move Polaris
halfway to the eyepiece’s center.
Figure 13. gently push the telescope horizontally to determine
direction of optical axis offset.
Figure 14a. Adjust the optical axis offset screws this way if
Polaris moves toward the center of the eyepiece when the tube is
pushed as in Figure 19.
Figure 14b. Adjust the
screws this way if Polaris
moves away from the center
of the eyepiece.

12
One-Year Limited Warranty
This Orion product 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 war‑
ranty period Orion Telescopes & Binoculars will repair or replace, at Orion’s option, any warranted instru‑
ment that proves to be defective, provided it is returned postage paid. Proof of purchase (such as a copy
of the original receipt) is required. This warranty is only valid in the country of purchase.
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. It is not
intended to remove or restrict your other legal rights under applicable local consumer law; your state or
national statutory consumer rights governing the sale of consumer goods remain fully applicable.
For further warranty information, please visit www.OrionTelescopes.com/warranty.
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