INSTRUCTION MANUAL
Orion® CT80 Compact 80mm
Equatorial Refractor
#9911
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
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Corporate Offices:
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IN 598 10/17
Congratulations on your purchase of an Orion telescope. Your new CT80 Equatorial Refractor is a terric
starter instrument for exploring the exotic wonders of the night sky. Designed to provide a wide eld of
view and excellent portability, 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 fascination, 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. Included Parts .............................2
2. Assembly .................................4
3. Preparing the Telescope for Operation ...........4
4. Understanding and Using the Equartorial Mount ...8
5. Astronomical Observing .....................11
6. Worthwhile Optional Accessories .............13
7. Telescope Care and Maintenance .............13
8. Specications .............................13
1. Included Parts
Unpack all of the parts and lay them out in your workspace.
Make sure all the parts listed below and shown in Figure 1
are present. Save the shipping box and packaging material. In
the unlikely event that you need to return the telescope, you
must use the original packaging. Initial assembly of the telescope is easy and should take only about 20 minutes.
Part Quantity
A – Tripod 1
B – Accessory tray 1
C – Equatorial mount 1
D – Counterweight shaft 1
E – Counterweight 1
F –Slow-motion cables 2
G – Tube mounting clamp 1
H – Optical tube assembly 1
I – Red dot nder scope 1
J –Star diagonal 1
K – 25mm Kellner eyepiece 1
L – 10mm Plossl eyepiece 1
M – Dust cover 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.
2
A
H
G
K
L
C
B
Figure 1. Parts of the CT80 EQ refractor
I J F
M E
D
3
2. Assembly
Refer to Figures 1 and 2 and the parts list at left for identica-
tion of specic parts during assembly.
1. Stand the tripod (A) upright and spread the legs apart.
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. To attach the accessory tray (B), place a hooked tab on
one of the three corners of the tray over the screw in the
leg collar, as shown in Figure 3A. Connect the tray to the
other two legs in the same manner (3B), then tighten all
three of the tray lock knobs (3C) to secure the tray in place.
3. Now you’ll install the equatorial mount (C) onto the tripod.
Remove the azimuth tension knob from the bottom of the
mount; the thin plastic gasket should be kept on (Figure
4). Then place the mount on the tripod’s mounting platform, inserting the base into the hole in the mounting
platform. Then replace the tension knob, turning the knob
clockwise to tighten the mount on the tripod (Figure 5).
4. Next, thread the counterweight shaft (M) into its receptacle
as shown in Figure 6A.
H G
I
K
J
F
A
F
E
C
D
Dec. Axis
R.A. Axis
L
5. To slide the counterweight (E) onto the counterweight
shaft, rst remove the Philips screw and washer from the
end of the shaft. You may need a Philips screwdriver for
this. Make sure the counterweight lock knob is loosened
enough so that the metal pin inside the counterweight is
clear of the shaft hole. Slide the counterweight about halfway up the shaft and secure it in place with the lock knob
(Figure 6B). Then replace the washer and screw at the end
of the counterweight shaft.
6. Attach the slow motion cables (F) to the gear shafts. The
longer cable should be attached to the declination gear
shaft; the shorter cable to the right ascension gear shaft
(see Figure 7). Orient the cable so that the slots in the
threaded end of the cable line up with the two pins on the
shaft (Figure 8A). Then thread the knurled nut on the shaft
onto the cable’s threads until tight (Figure 8B).
Now the mount is properly attached to the tripod and outtted
for use. Next, you’ll attach the tube mounting clamp (G) and
optical tube (H) to the EQ mount.
7. Remove the wing nuts and washers from the two screws
of the tube mounting clamp.
8. Now insert the screws into the holes in the equatorial
mount’s saddle plate (Figure 9A). Then replace the wash-
ers and wing nuts on the screws and tighten them to
secure the mounting clamp (Figure 9B).
9. Open the mounting clamp and lay the telescope optical
tube in the clamp. Then close the clamp around the tube
and lock it by hooking the D-ring over the upper clamp
ange as shown in Figure 10, then press the lock latch
down.
10. With the tube now secure in the mounting clamp, attach
the red dot nder scope (I) to the optical tube. Do this by
orienting the nder scope as shown in Figure 11 and slide
the bracket foot back into the nder scope base as far as it
will go.
11. Insert the star diagonal (J) into the focuser drawtube and
tighten the thumbscrew on the drawtube collar. Then insert
the 25mm eyepiece (K) into the diagonal and secure it by
lightly tightening the thumbscrew on the diagonal (Figure
12).
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.
Wingnut
B
Figure 2.
4
The fully assembled CT80 EQ refractor.
3. Preparing the Telescope
for Operation
Aligning and Using the Red Dot Finder Scope
The included red dot nder scope (I) makes pointing your telescope almost as easy as pointing your nger! It’s a non-magnifying aiming device that superimposes a tiny LED-illuminated 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.
Hooked tab
Lock knob
Accessory
tray
Screw
Leg collar
A
B
C
Figure 3. A) Hook the tray corner over the screw in the leg collar, B) Repeat for the other two legs, then C) Tighten all three tray lock knobs.
Before you can use the red dot nder scope, you must remove
the tab sticking out from the battery compartment (Figure 13).
Doing so will allow the pre-installed 3V CR-2032 button cell battery to make contact with the nder scope’s electronic 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 (M) from the front of the telescope.
2. With the star diagonal and 25mm eyepiece already in
place from step 11 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 as needed to point
the telescope. For larger telescope movement, release the
R.A. and Dec. axis lock knobs (Figure 7) and move the
telescope tube by hand to the approximate location, then
Gasket
Figure 4.
tension knob.
To install the equatorial mount, rst remove the azimuth
Gasket
Azimuth tension
knob
Figure 5. Place the equatorial mount on the tripod, then secure
it with the azimuth tension knob.
5
A B
Figure 6. A) Thread the counterweight into its receptacle. B)
Remove the screw and washer from the end of the shaft, then slide
the counterweight on and secure it with the counterweight lock knob.
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 13). Position
your eye at a comfortable distance from the rear of the
unit. Look through the round window 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.
Declination
Saddle
Slow-motion
cable, R.A.
Declination
setting
circle
Right
ascension axis
Latitude
lock bolt
Gear shaft,
R.A.
Pointer
Gear shaft Declination
Right ascension
setting circle
Pointer
Latitude scale
Latitude
adjustment bolt
Slow-motion cable, Declination
Figure 7. The CT80’s equatorial mount.
6
Gear shaft
Knurled
knob
Pins
Slots
Slow-motion
cable
Tube
mounting
clamp
Saddle
A
B
Figure 8.
shown, B) then thread the knurled nut into the threaded end of the
cable until tight.
A) Slide the slow-motion cable onto the gear shaft as
NOTE: This nder has two brightness settings. When the
switch is set all the way over to the ON position, the red dot
is brightest. But in between the OFF and ON positions is a
middle setting in which the red dot is dim. Typically the dim
setting is used under dark skies and the brighter setting is
used under light-polluted skies or in daylight.
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
13) 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.
A
Mounting
clamp
Washer
Wing
nut
B
Figure 9. A) Install the tube mounting clamp onto the mount
saddle. B) Secure the clamp to the saddle with the two wing nuts.
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.
D-ring
Upper
clamp
ange
Lock latch
Figure 10. Lay the optical tube in the open clamp, then close the
clamp and lock it in with the lock latch.
7
Finder
scope
base
Figure 11. Slide the red dot nder scope’s bracket into its base.
Balancing the Telescope
In order for the telescope to move smoothly on its mechanical
axes, it must rst be balanced as follows:
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 rotate freely
about the R.A. axis. Rotate it until the counterweight shaft
is parallel to the ground, i.e., horizontal (Figure 14A).
2. Now loosen the counterweight lock knob and slide the
weight along the shaft until it exactly counterbalances the
telescope. That’s the point at which the shaft remains horizontal even when you let go of the telescope with both
hands.
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, rst 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. The telescope should now be able to rotate
freely about the Dec. axis (Figure 14B). If the tube rotates
on its own due to imbalance, you will need to reposition it a
little forward or back in the tube clamp until it is balanced.
Drawtube
tension knob
Accessory
collar
Eyepiece
Star
diagonal
Figure 12. Install the diagonal and eyepiece in the focuser as
shown.
Power switch
Ta b
Battery compartment
Opposite side
Vertical
adjustment
knob
Horizontal
adjustment
knob
Figure 13. The red dot nder scope has vertical and (inset)
horizontal adjustment knobs for aligning it with the telescope.
(You’ll have to unlatch the clamp’s lock latch to do this.)
Then re-tighten the Dec. lock knob.
When you are actually observing with the telescope, you can
adjust the eyepiece and focuser orientation by unlatching the
tube clamp and rotating the optical tube to the desired position.
Be sure to hold onto the tube when you unlatch the clamp!
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.
4. Understanding and Using
the Equatorial 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 7). 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 R.A. 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.
8
R.A. lock
knob
Dec. lock
knob
Figure 14. To balance the telescope on the mount, you rst
A) balance it on the R.A. axis, then B) on the Declination axis.
To nd Polaris in the sky, look north and locate the pattern of
the Big Dipper (Figure 15). The two stars at the end of the
“bowl” of the Big Dipper point approximately 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 CT80’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 bolt located on the front of the
mount (see Figure 7). Turn the latitude adjustment bolt (on
the opposite side of the mount) until the pointer on the
latitude scale is indicating the latitude of your observing
location. 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 lightly retighten the latitude lock
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, 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 7) 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.
NOTE: You can do the polar alignment with the telescope
attached to the equatorial mount.
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 render
the polar alignment inaccurate. The telescope should be moved
only about its R.A. and Dec. axes.
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
7) 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
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
Little Dipper
(in Ursa Minor)
Big Dipper
(in Ursa Major)
Pointer
Stars
N.C.P.
Polaris
Cassiopeia
Figure 15. 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).
9
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 must be reset. This is done by rst
rotating the control cable several turns in the opposite direction from 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.
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. 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.
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
The two setting circles (Figure 7B) 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
apply to viewing in the Northern Hemisphere.
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.
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.
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.
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.
10
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 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!
“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).
Star-Testing the Telescope
When it is dark, point the telescope at a bright star and accurately center it in the eyepiece’s eld of view. Slowly de-focus the
image with the focus knob. If the telescope’s optics are correctly
aligned, the expanding disk should be a perfect circle (Figure
16). If the image is unsymmetrical, the optics are out of alignment. The dark shadow cast by the secondary mirror should
appear in the very center of the out-of-focus circle, like the hole
in a donut. If the “hole” appears off-center, the optics are out of
alignment.
If you try the star test and the bright star you have selected
is not accurately centered in the eyepiece, the telescope will
appear to need collimating, even though the optics may be
perfectly aligned. It is critical to keep the star centered, so over
time you will need to make slight corrections to the telescope’s
position in order to account for the sky’s apparent motion.
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 CT80 EQ refractor comes with 25mm
and 10mm 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)
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For example, the CT80 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 CT80 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!
So start by using the 25mm eyepiece, then try switching to the
10mm eyepiece later if you want to boost the magnication.
Focusing the Telescope
To focus the telescope, turn the focus wheels (Figure 12)
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
focus a bit to get a sharp image with the newly inserted eyepiece.
On the top of the focuser housing is the drawtube tension
knob (Figure 12). Use it to adjust the amount of friction on
the motion of the focuser drawtube when turning the focus
wheels.
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 such as star clusters and nebulas. Do not expect to see
colors in faint objects as you do in photographs, however. Most
galaxies and nebulas will appear gray in color. Unlike a camera,
which can record colors of faint objects in long exposures, our
eyes are not sensitive enough to see such color 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.
B. 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 two-color 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
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 you nd an
observing site well away from light pollution.
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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.
• 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 magnify-
ing 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.
• 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
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
Lens coatings: Fully antireection coated
Focuser: Rack-and-pinion, accepts 1.25" accessories
Eyepieces: 25mm Kellner and 10mm Plossl, 1.25" barrel
diameter, threaded for Orion lters
Eyepiece coatings: Fully antireection coated
Diagonal: Mirror, 1.25"
Eyepiece magnication: 16x (with 25mm eyepiece) and 40x
(with 10mm eyepiece)
Finder scope: Red dot nder scope, two brightness levels
Mount: German equatorial
Tripod: Aluminum
Motor drive: Optional
Total instrument weight: 15 lbs. 9 oz.
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
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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 defective, 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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