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INSTRUCTION MANUAL
Orion® Observer™ 80ST
Equatorial Refractor
#10273
Providing Exceptional Consumer Optical Products Since 1975
All Rights Reserved. No part of this product instruction or any of its contents may be reproduced, copied,
modied or adapted, without the prior written consent of Orion Telescopes & Binoculars.
®
Copyright © 2017 Orion Telescopes & Binoculars
Customer Support:
www.OrionTelescopes.com/contactus
Corporate Offices:
89 Hangar Way, Watsonville CA 95076 – USA
IN 582 05/17
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Congratulations on your purchase of an Orion telescope. Your new Observer 80ST Equatorial Refractor is
a terric starter instrument for exploring the exotic wonders of the night sky. Designed to be compact and
easy to use, it will provide many hours of enjoyment for the whole family.
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. With a little practice, a little patience, and a reasonably dark sky away from city lights, you’ll
nd 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 .................................2
2. Assembly .................................4
3. Preparing the Telescope for Operation ...........5
4. Understanding and Using the Equartorial Mount ...7
5. Astronomical Observing .....................10
6. Worthwhile Optional Accessories .............12
7. Telescope Care and Maintenance .............13
8. Specications .............................13
1. Parts List
Part. Quantity
A – Tripod legs 3
B – Hex head tripod mounting bolts (3”) 3
C – Washers (5/8”) 3
D – Wing nuts 3
E – Leg lock thumbscrews 3
F – Accessory tray 1
G – Screws 3
H – Washers (3/8”) 3
I – Wing nuts (small) 3
J – Equatorial mount 1
K – Azimuth lock knob (and washer) 1
L – Latitude adjustment bolt 1
M – Counterweight shaft 1
N – Counterweight lock knob 1
O – Counterweight 1
P – Slow-motion cables 2
Q – Mounting platform 1
R – Telescope optical tube 1
S – Red dot nder scope 1
T – Dust cover 1
U – 25mm Kellner eyepiece 1
V- 10mm Kellner eyepiece 1
W – Star diagonal 1
WARNING: Never look directly at the Sun through
your telescope—even for an instant—without a
professionally made solar lter 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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Q
A
R
T
L
O
B
N
P
C
K
D
JIHGFMVSUWE
Figure 1. The parts of the Observer 80ST EQ telescope .
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2. Assembly
R
S
J
R.A. Axis
(R.A.)
P
N
O
U
P
W
Q
(Dec)
M
L
K
A
F
Dec. Axis
A
E
E
A
E
Figure 2. The Observer 80ST EQ telescope fully assembled, with
key parts identied.
Wingnut
Washer
Figure 3. a) Attach the three tripod legs to the mount platform,
b) making sure the bolt’s hex-shaped head seats in the hex-shaped
recess of the tripod leg.
1. Attach the three aluminum tripod legs (A) to the mounting
platform (Q) (Figure 3a) with the three hinged leg braces
facing inward. Three hex-head bolts (B) each about 3" long,
with 5/8” washers (C) and wing nuts (D), are provided for
this purpose. Note that the bolts should be inserted from
the side of the leg that has the hex-shaped hole, so that
the bolt head seats in the hex-shaped hole (Figure 3b).
The washer then the wing nut are placed on the opposite
side on the exposed end of the bolt.
2. Attach a leg lock thumbscrew (E) to each leg as shown
(Figure 4). Extend the sliding inner portion of the adjustable-height tripod leg to the desired length for all three
legs. Lock in place by tightening the leg lock thumbscrews.
Do not over-tighten the leg lock thumbscrews or you
may damage the collar they are attached to.
3. Now stand the tripod upright, spreading the legs evenly
apart so the accessory tray can be positioned to attach to
the three leg braces.
4. Attach the accessory tray (F) to the leg brace supports
(Figure 5) with the three short screws (G), small (3/8”)
washers (H), and small wing nuts (I) provided. Place a
washer on the screw. Then place the accessory tray on
top of one of the leg braces so that the mounting screw
passes through the hole at one of the corners of the
accessory tray, and through the slot in the leg brace. Then
place another small washer on the screw and thread on
and tighten the wing nut. Repeat this procedure until the
tray is attached to all three leg braces.
The tripod is now fully assembled (Figure 6)
install the equatorial mount onto the tripod.
5. Locate the equatorial (EQ) mount (J) and place its base
into the hole in the center of the mounting platform (Q)
(Figure 7a). Then secure it in place with the azimuth lock
knob and washer (K) (Figure 7b).
6. Thread the latitude adjustment bolt (L) into the threaded
socket (Figure 8) until it contacts metal inside the housing.
7. Next, thread the counterweight shaft (M) into the base of
the Declination axis of the mount (Figure 9).
8. Thread the counterweight lock knob (N) into the counterweight (O) a few turns.
9. To slide the counterweight onto the counterweight shaft,
rst remove the Philips screw and washer from the end
of the shaft. Make sure the counterweight lock knob (N) is
loosened enough so that the metal pin inside the counterweight is clear of the shaft hole. Slide the counterweight
about 2 inches from the bottom of the counterweight shaft
and secure it in place with the lock knob (Figure 10). Then
replace the washer and screw at the end of the counterweight shaft.
10. Attach the slow motion cables (P) to the gear shafts as
shown in Figure 11. The longer cable should be attached
to the declination gear shaft; the shorter cable to the right
ascension gear shaft. Orient the cable so that the thumb-
. Next you will
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Accessory tray
Screw head
Washer
Washer
Wing nut
Leg
Figure 4.
shown, being careful not to overtighten.
Now the mount is properly attached to the tripod and outtted
for use (Figure 13). Next, you’ll attach the telescope optical
tube to the mount.
11. Remove the wing nuts and washers from the optical tube
12. To attach the red dot nder scope (S) to the optical tube,
13. Insert the star diagonal (W) into the focuser drawtube and
The telescope is now completely assembled! Before it can be
effectively used, however, there are a couple of things to do to
prepare the telescope for operation.
Thread a leg lock thumbscrew onto each tripod leg as
screw seats in the groove of the gear shaft, as shown in
Figure 12, then rmly tighten the thumbscrew. If there is
a small rubber ball on the end of the shaft, you will have
to remove it in order to attach the cable. Also note that,
depending on your preference, you can attach the cable to
either the left or right side of the right ascension gear shaft.
mounting bolts that are pre-installed on the underside
of the telescope optical tube (R). Then lay the telescope
optical tube assembly onto the saddle plate (Figure 14),
passing the mounting bolts through the holes in the saddle
plate. Then place a washer on each bolt and re-attach the
wing nuts until tight. Be sure the focuser portion of the
optical tube is on the same side of the saddle as the slowmotion control cable in Declination, as in Figure 14.
orient the nder scope as shown in Figure 15 and slide
the bracket foot into the nder scope base until it clicks.
(To remove the nder scope, press the small tab at the
back of the base and slide the bracket out.)
tighten the two thumbscrews on the drawtube collar (Figure
16). Then insert the 25mm eyepiece (U) into the diagonal
and secure it by lightly tightening the thumbscrew on the
diagonal.
Figure 5. Attach the accessory tray to each of the tripod three
leg brace supports using the provided hardware.
The included red dot nder scope (Figure 17) makes pointing
your telescope almost as easy as pointing your nger! It’s a nonmagnifying aiming device that superimposes a tiny LED red dot
on the sky, showing exactly where the telescope is pointed. It
permits easy object targeting prior to observation in the higherpower main telescope.
Before you can use the red dot nder scope, you must remove
the small plastic tab sticking out from the battery compartment
(Figure 17). Doing so will allow the pre-installed 3V CR-2032
3. Preparing the Telescope
for Operation
Aligning and Using the Red Dot Finder Scope
Figure 6. The fully assembled tripod.
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button cell battery to make contact with the nder scope’s elec-
Washer
Azimuth
lock knob
Figure 7. a) Install the equatorial mount onto the tripod mount
platform, then b) secure it from the underside with azimuth lock knob.
tronic circuitry to power the nder’s red LED illuminator. The tab
can then be discarded.
To use the red dot nder scope properly, it must be aligned with
the main telescope. This is easiest to do during daylight hours,
before observing at night. Follow this procedure:
1. First, remove the dust cap (T) from the front of the telescope.
2. With the star diagonal and 25mm eyepiece already in
place from step 13 above, point the telescope at a welldened land target (e.g., the top of a telephone pole) that’s
at least a quarter mile away. Center the target in the eyepiece by turning the slow-motion cables (P) as needed
to point the telescope. For larger telescope movement,
release the R.A. and Dec. axis lock knobs (Figure 18) and
move the telescope tube by hand to the approximate location, then retighten the lock knobs and make ner pointing
adjustments with the slow motion cables.
Note: The image in the telescope will appear mirror reversed,
i.e., reversed left to right. This is normal for refractor telescopes used for astronomical observing with a standard star
diagonal. (For terrestrial observing we recommend using an
optional “correct image” diagonal, which will serve up a correctly oriented view.)
3. Now that a distant target is centered in the main telescope’s eyepiece, turn on the red dot nder scope by sliding the power switch to ON (refer to Figure 17). The “1”
position provides dim illumination while the “2” position
provides brighter illumination. Typically the dimmer setting
is used under dark skies and the brighter setting is used
under light-polluted skies or in daylight. Position your eye
at a comfortable distance from the rear of the unit. Look
through the rear of the nder scope with both eyes open
to see the illuminated red dot. The target object should
appear in the eld of view somewhere near the red dot.
4. You’ll want to center the target object on the red dot. To do
so, without moving the telescope, use the nder scope’s
vertical and horizontal adjustment knobs (shown in Figure
17) to position the red dot on the object.
5. When the red dot is centered on the distant object, check
to make sure the object is still centered in the telescope’s
eyepiece. If it isn’t, re-center it then adjust the finder
scope’s alignment again. When the object is centered in
the telescope eyepiece and on the nder scope’s red dot,
the nder scope is properly aligned with the telescope.
The red dot nder scope’s alignment should be checked
before every observing session.
At the end of your observing session, be sure to slide the power
switch on the red dot nder scope to OFF to preserve battery life.
Balancing the Telescope
In order for the telescope to move smoothly on its mechanical
axes, it must rst be balanced as follows:
1. Loosen the R.A. lock knob half a turn or so (Figure 19).
With the R.A. lock knob loosened, the telescope mount
will turn freely about the polar (R.A.) axis. Rotate the telescope about the polar axis so that the counterweight shaft
is parallel to the ground (horizontal), as shown.
Latitude adjustment
bolt
Figure 8. Screw in the latitude adjustment bolt.
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Figure 9. Thread the counter-
weight shaft into the declination
housing.
Lock knob
Figure 10. The
counterweight, installed.
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Dec. slowmotion cable
Latitude adjustment
bolt
Figure 11.
motion cables attached.
Gear shaft
Rear view of the equatorial mount, with the two slow-
Groove
R.A. slowmotion cable
Latitude lock
knob
Thumbscrew
Slow-motion
cable
Figure 12. Line up the slow-motion cable thumbscrew with the
groove in the gear shaft, then tighten.
2. Loosen the counterweight lock knob and slide the counterweight along the shaft until the telescope remains in any
given position without tending to drift up or down relative
to the polar axis (Figure 19). Then retighten the counter-
weight lock knob, locking the counterweight in that position. If you can’t tell where the balance point is, just set the
counterweight halfway up the counterweight shaft and lock
it there.
The telescope is now balanced.
4. Understanding and Using
the Equartorial Mount
When you look at the night sky, you no doubt have noticed
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 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 eld of view while you’re observing.
An equatorial mount has two perpendicular axes: right ascension and declination (Figure 18). The R.A. axis, also known as
the “polar” axis, can be aligned to be parallel with the Earth’s
axis of rotation, thus allowing easy tracking of the night sky.
This is accomplished by slowly rotating the telescope on its
R.A. axis. The process of aligning the mount’s R.A. axis with
the Earth’s rotational (polar) axis is called polar alignment.
Polar Alignment
For Northern Hemisphere observers, approximate polar alignment is achieved by pointing the mount’s right ascension axis
at the North Star (Polaris). It lies within 1° 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 the NCP.
To nd Polaris in the sky, look north and locate the pattern of the
Big Dipper (Figure 20). 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).
To polar align the Observer 80ST’s equatorial mount:
1. Roughly level the equatorial mount by adjusting the length
of the three tripod legs as needed.
2. Loosen the latitude lock knob (see Figure 11). Turn the lat-
itude adjustment bolt until the pointer on the latitude scale
is indicating the latitude of your observing location (Figure
18). If you don’t know your latitude, you can look it up on
the internet. For example, if your latitude is 35° North, set
the pointer to 35. Then retighten the latitude lock knob.
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, as it is in Figure
2. The pointer on the Dec. setting circle should read 90°.
Retighten the Dec. lock knob.
4. Loosen the azimuth lock knob at the base of the equatorial
mount (Figure 18) and rotate the mount so the R.A. axis
points roughly at Polaris. If you cannot see Polaris directly
from your observing site, consult a compass and rotate the
mount so the telescope points North. Retighten the azimuth lock knob.
The equatorial mount is now polar aligned. From this point
on in your observing session, you should not make any
further adjustments to 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.
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Figure 13. The fully assembled equatorial mount.
Eyepiece
Focus
drawtube
Diagonal
Focus
wheels
Figure 16. Secure the star diagonal in the focuser drawtube with
the two thumbscrews, then secure the eyepiece in the diagonal.
Power switch
Saddle
Washer
Washer
Wing nut
Figure 14. Attach the optical tube to the mount’s saddle plate with
the supplied wingnuts and washers.
Finder Scope
Base
Bracket
foot
Figure 15. Insert the red dot nder scope’s bracket into the base
near the focuser as shown.
Plastic
tab
Opposite side
Vertical knob
Horizontal knob
Figure 17. The red dot nder scope has vertical and (inset)
horizontal adjustment knobs for aligning it with the telescope.
Using 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 eld of view. Before using the cables, 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
(Figure 18) 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 eld of
view of the red dot nder scope. If it isn’t, use the slow-motion
controls to scan the surrounding area of sky. Note: when
using the slow motion cables, the R.A. and Dec lock
knobs should be tightened, not loose. When the object
is visible in the nder scope, use the slow-motion controls to
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Latitude
adjustment
bolt
Latitude
lock knob
Declination (Dec.) axis
Dec. Setting circle
R.A. lock
knob
R.A. Setting
circle
Dec. lock
knob
Declination (Dec.) axis
Latitude
scale
R.A.
Setting
circle
Dec. Slowmotion
cable
Dec. Slowmotion
cable
R.A. Slow-motion cable
Figure 18. Components of the equatorial mount, seen from both sides.
center the red dot on it. Now, look in the telescope’s eyepiece
and use the slow-motion controls to center it in the eyepiece.
The Dec. slow-motion control cable can move the telescope a
maximum of 25° or so. 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 slowmotion mechanism must be reset. This is done by rst rotating
the control cable several turns in the opposite direction from
Tracking Celestial Objects
When you observe a celestial object through the telescope,
you’ll see it drift slowly across the eld of view. To keep it in the
eld, assuming your equatorial mount is polar aligned, just turn
the R.A. slow-motion control cable clockwise, if the slow-motion
cable is mounted on the EAST side of the mount. If it’s on the
WEST side of the mount, turn it counterclockwise to track. The
Dec. slow-motion control cable is not needed for tracking. Objects
will appear to move faster at higher magnications, because the
eld of view is narrower.
which it was being turned. Then, manually slew the telescope
closer to the object you wish to observe (remember to rst
loosen the Dec. lock knob). You should now be able to use the
Dec. slow-motion control cable again to ne adjust the telescope’s position.
Optional Electronic Drives for Automatic Tracking
An optional DC electronic drive can be mounted on the R.A. axis
of the equatorial mount to provide hands-free tracking. Objects
will then remain stationary in the eld of view without any manual
adjustment of the R.A. slow-motion control cable.
Understanding the Setting Circles
R.A. lock knob
The two setting circles (Figure 18) on an equatorial mount
enable you to locate celestial objects by their “celestial coordinates”. Every object resides in a specic 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 mount’s R.A. setting circle is scaled in hours, from 1 through
24, with small marks in between representing 10-minute increments. The numbers closest to the R.A. axis gear apply to viewing in the Southern Hemisphere, while the numbers above them
Figure 19. Balance the telescope on the R.A. axis by positioning
it as shown and sliding the counterweight until balance is achieved.
apply to viewing in the Northern Hemisphere.
Azimuth
lock knob
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Little Dipper
(in Ursa Minor)
Big Dipper
(in Ursa Major)
Pointer
Stars
N.C.P.
Polaris
Cassiopeia
Figure 20. To nd Polaris in the night sky, look north and nd the
Big Dipper. Extend an imaginary line from the two "Pointer Stars"
in the bowl of the Big Dipper. Go about ve times the distance
between those stars and you'll reach Polaris, which lies within 1° of
the north celestial pole (NCP).
The Dec. setting circle is scaled in degrees, with each mark representing 2.5° 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, while 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 are:
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 arc-minutes in 1 degree of declination).
Before you can use the setting circles to locate objects, the
mount must be properly 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.
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 whose coordinates
you know. Lock the R.A. and Dec. lock knobs. Center the
star in the telescope’s eld of view with the slow-motion
control cables.
4. Rotate the setting circle until the metal arrow indicates the
R.A. coordinate listed in the star atlas for the object.
Finding Objects with the Setting Circles
1. Now that both setting circles are calibrated, look up in a
star atlas the coordinates of an object you wish to view.
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 upper set
of numbers on the R.A. setting circle. Retighten the lock
knob.
3. 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.
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 eld of view of the red dot
nder scope, assuming the equatorial mount is accurately polar
aligned. Use the slow-motion controls to center the object in the
nder scope, and it should appear in the telescope’s eld of view.
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.
Calibrating the Right Ascension Setting Circle
1. Identify a bright star in the sky near the celestial equator
(Dec. = 0°) and look up its coordinates in a star atlas.
Figure 21. The Kellner eyepieces have barrels threaded to
accept optional Orion 1.25" lters. A Moon lter is useful for cutting
glare and revealing more detail on the lunar surface.
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Confused About Pointing the Telescope?
Beginners occasionally experience some confusion about how
to point the telescope overhead or in other directions. One thing
you DO NOT do is make any adjustment to the mount’s latitude
setting or to its azimuth position (don’t touch the azimuth lock
knob). That will throw off the mount’s polar alignment. Once the
mount is polar aligned, the telescope should be moved only
about the R.A. and Dec. axes by loosening one or both of the
R.A. and Dec. lock knobs and moving the telescope by hand, or
keeping the knobs tightened and moving the telescope using the
slow-motion cables.
5. Astronomical Observing
For many, this will be your rst foray into the exciting world of
amateur astronomy. The following information and observing
tips will help get you started.
Choosing an Observing Site
When selecting a location for observing, get as far away as possible from direct articial light such as street lights, porch lights,
and automobile headlights. The glare from these lights will great-
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ly 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!
“Seeing” and Transparency
Atmospheric conditions vary signicantly 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 you look up at the sky and stars are twinkling noticeably,
the seeing is poor and you will be limited to viewing at lower
magnications. At higher magnications, images will not focus
clearly. Fine details on the planets and Moon will likely not be
visible.
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.
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 (5th or 6th magnitude is desirable).
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 30 minutes for
your telescope to acclimate to the temperature outdoors before
you start observing with it.
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-ltered ashlight rather than a white light. Red light does not spoil your eyes’
dark adaptation like white light does. A ashlight with a red LED
light is ideal. Beware, too, that nearby porch, streetlights, and car
headlights will ruin your night vision.
Eyepiece Selection
Magnication, or power, is determined by the focal length of
the telescope and the focal length of the eyepiece being used.
Therefore, by using eyepieces of different focal lengths, the
resultant magnication can be varied. It is quite common for an
observer to own ve or more eyepieces to access a wide range
of magnications. This allows the observer to choose the best
eyepiece to use depending on the object being viewed and viewing conditions. Your Observer 80ST EQ refractor comes with
25mm and 10mm Kellner eyepieces, which will suffice nicely to
begin with. You can purchase additional eyepieces later if you
wish to have more magnication options.
Magnication is calculated as follows:
Telescope Focal Length (mm)
= Magnication
Eyepiece Focal Length (mm)
For example, the Observer 80ST EQ has a focal length of
400mm, which when used with the supplied 25mm eyepiece
yields:
400 mm
= 16x
25 mm
The magnication provided by the 10mm eyepiece is:
400 mm
= 40x
10 mm
The maximum attainable magnication for a telescope is directly
related to how much light it can gather. The larger the aperture,
the more magnication is possible. In general, a gure of 50x per
inch of aperture is the maximum attainable for most telescopes.
Going beyond that will yield simply blurry, unsatisfactory views.
Your Observer 80ST EQ has an aperture of 80mm, or 3.1 inches, so the maximum magnication would be about 155x (3.1 x
50). This level of magnication assumes you have ideal atmospheric conditions for observing (which is seldom the case).
Keep in mind that as you increase magnication, the brightness
of the object viewed will decrease; this is an inherent principle
of the laws of physics and cannot be avoided. If magnication is
doubled, an image appears four times dimmer. If magnication is
tripled, image brightness is reduced by a factor of nine!
Start by centering the object you wish to see in the 25mm eyepiece. Then you may want to increase the magnication to get a
closer view, by switching to the 10mm eyepiece. If the object is
off-center (i.e., it is near the edge of the eld of view) you will lose
it when you increase magnication, since the eld of view will be
narrower with the higher-powered eyepiece. So make sure it is
centered in the 25mm eyepiece before switching to the 10mm
eyepiece.
Focusing the Telescope
To focus the telescope, turn the focus wheels (Figure 16)
forward or back until you see your target object (e.g., stars,
the Moon, etc.) in the eyepiece. Then make ner adjustments
until the image is sharp. If you’re having trouble achieving initial focus, rack the focuser drawtube all the way in using the
focus wheels, then while looking into the eyepiece slowly turn
the focus wheels so that the drawtube extends outward. Keep
going until you see your target object come into focus. Note
that when you change eyepieces you may have to adjust the
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focus a bit to get a sharp image with the newly inserted eyepiece.
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 many bright deep-sky
objects. Do not expect to see color as you do in NASA photos,
since those are taken with long-exposure 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.
Objects to Observe
Now that you are all set up and ready to go, one critical decision
must be made: what to look at?
A. The Moon
With its rocky surface, the Moon is one of the easiest and most
interesting objects to view with your telescope. Lunar craters,
maria, and even mountain ranges can all be clearly seen from
a distance of 238,000 miles away! With its ever-changing phases, you’ll get a new view of the Moon every night. 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 are cast on the surface, which 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. Make sure
to observe the Moon when it is well above the horizon to get the
sharpest images.
Use an optional Moon lter to dim the Moon when it is very bright.
It simply threads onto the bottom of the eyepieces (you must rst
remove the eyepiece from the focuser to attach a lter). You’ll nd
that the Moon lter improves viewing comfort, and helps to bring
out subtle features on the lunar surface.
B. The Planets
The planets don’t stay put like the stars, so to nd them you
should refer to the monthly star charts at OrionTelescopes.com,
or to charts published monthly in Astronomy, Sky & Telescope, or
other astronomy magazines. Venus, Mars, Jupiter, and Saturn are
the brightest objects in the sky after the Sun and the Moon. Other
planets may be visible but will likely appear star-like. Because
planets are quite small in apparent size, optional higher-power
eyepieces or a Barlow lens are recommended and often needed
for detailed observations.
C. The Sun
You can change your nighttime telescope into a daytime Sun
viewer by installing an optional full-aperture solar lter over the
front opening of the telescope. 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 lter, or permanent eye damage could result.
D. The Stars
Stars will appear like twinkling points of light. Even powerful telescopes cannot magnify stars to appear as more than a point
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 twocolor double star Albireo in Cygnus are favorites. Defocusing a
star slightly can help bring out its color.
E. Deep-Sky Objects
Under dark skies, you can observe a wealth of fascinating deepsky 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 you nd an observing site well
away from light pollution.
To nd deep-sky objects with your telescope, you rst need to
become reasonably familiar with the night sky. Unless you know
how to recognize the constellation Orion, for instance, you won’t
have much luck locating the Orion Nebula. A simple planisphere,
or star wheel, can be a valuable tool for learning the constellations and seeing which ones are visible in the sky on a given
night. Once you have identied a few constellations, a good star
chart, atlas, or astronomy app will come in handy for helping
locate interesting deep-sky objects to view within the constellations.
Do not expect these objects to appear like the photographs you
see in books and on the internet; most will look like dim gray
smudges. Our eyes are not sensitive enough to see color in
deep-sky objects except in a few of the brightest ones. But as you
become more experienced and your observing skills get sharper,
you will be able to ferret out more and more subtle details and
structure.
6. Worthwhile Optional
Accessories
• Moon Filter – A 1.25” Moon lter will cut down the strong glare
of sunlight reected from the Moon, making Moon viewing
more comfortable and revealing more surface detail. The lter
threads into the bottom of the Kellner eyepieces that came
with your telescope (Figure 21).
• Motor Drive – A motor drive, which attaches to the right
ascension axis of an equatorial telescope mount, enables
your telescope to “track” the motion of stars and other celestial objects as they drift slowly from east to west in the night
sky. This keeps them in the eyepiece eld of view indenitely,
instead of drifting out of sight.
• Barlow Lens – A 2x Barlow lens doubles the magnifying
power of any eyepiece it’s used with, giving you a big power
boost to get in closer to your target object. You just insert it
between the diagonal and the eyepiece.
• Planisphere – A nifty “star wheel” that shows what stars and
constellations are visible in the sky at any time of any night.
Just set the date and time see a mini representation of your
local night sky. Great for identifying what you see and planning an evening’s observing session.
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• Star Map – More detailed than a planisphere, a star map is
essential for locating interesting celestial objects to observe
with your telescope. Nowadays many mobile astronomy apps
feature customizable star maps that you can access on your
smartphone or tablet while you’re at the telescope.
7. Telescope 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 dust cover on the front
of the telescope when it is not in use.
Your refractor telescope requires very little mechanical maintenance. The optical tube has a smooth painted nish 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 touchup paint to the scratch. Smudges on the tube can be wiped off
with a soft cloth and household cleaning uid.
Cleaning Optics
Any quality optical lens cleaning tissue and optical lens cleaning
uid specically designed for multi-coated optics can be used
to clean the lenses of your telescope and eyepieces. Never use
regular glass cleaner or cleaning uid designed for eyeglasses.
Before cleaning, remove any loose particles or dust from the lens
with a blower bulb or soft brush. Then apply some cleaning uid
to a tissue, never directly on the optics. Wipe the lens gently in
a circular motion, then remove any excess uid with a fresh lens
tissue. Oily ngerprints and smudges may be removed using this
method. Use caution; rubbing too hard may scratch the lens. On
larger lenses, clean only a small area at a time, using a fresh
lens tissue on each area. Never reuse tissues.
When bringing the telescope inside after an evening’s viewing
it is normal for moisture to accumulate on the lenses due to the
change in temperature. We suggest leaving the telescope and
eyepieces uncovered overnight to allow the condensation to
evaporate.
8. Specifications
Objective lens: 80mm (3.1") diameter, achromatic
Effective focal length: 400mm
Focal ratio: f/5.0
Lens coatings: Antireection coated
Focuser: Rack-and-pinion, accepts 1.25" accessories
Eyepieces: 25mm and 10mm Kellner, antireection coated, 1.25"
barrel diameter, threaded for Orion lters
Eyepiece magnication: 16x (with 25mm eyepiece) and 40x
(with 10mm eyepiece)
Finder scope: Red dot nder scope
Mount: German equatorial
Tripod: Aluminum
Motor drive: Optional
Total instrument weight: 11 lbs. 3 oz.
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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 benet 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 defec-
tive, provided it is returned postage paid. Proof of purchase (such as a copy of the original receipt) is required. This
This warranty does not apply if, in Orion’s judgment, the instrument has been abused, mishandled, or modied, nor
does it apply to normal wear and tear. This warranty gives you specic 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
For further warranty information, please visit www.OrionTelescopes.com/warranty.
Corporate Offices: 89 Hangar Way, Watsonville CA 95076 - USA
Customer Support: www.OrionTelescopes.com/contactus
All Rights Reserved. No part of this product instruction or any of its contents may be reproduced, copied, modified or adapted, without the prior
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warranty is only valid in the country of purchase.
governing the sale of consumer goods remain fully applicable.
Orion® Telescopes & Binoculars
Copyright © 2017 Orion Telescopes & Binoculars
written consent of Orion Telescopes & Binoculars.
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