Orion STARMAX 90 EQ User manual

INSTRUCTION MANUAL
IN 162 Rev. C 06/08
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
OrionTelescopes.com
Orion®
StarMax™90 EQ
#9821 Equatorial Maksutov-Cassegrain Telescope

2
Figure 1. Orion StarMax 90mm EQ
Mounting block
Counterweight shaft
Right Ascension
slow‑motion control
Counterweight
Counterweight lock knob
Tripod leg
Finder scope bracket
Finder scope
Eyepiece
Star diagonal
Declination
slow motion control
Accessory tray
Accessory tray bracket
Leg lock knob

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1. Unpacking
The entire telescope system will arrive in one box. Be careful
unpacking the box. We recommend keeping the original ship‑
ping container. In the event that the telescope needs to be
shipped to another location, or returned to Orion for warranty
repair, having the proper shipping container will help ensure
that your telescope will survive the journey intact.
Make sure all the parts in the Parts List are present. Be
sure to check 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
Qty. Description
1 Optical tube assembly
1 Optical tube dust cover
1 25mm (50x) Sirius Plössl eyepiece (1.25")
1 Mirror star diagonal
1 6x20 correct‑image finder scope
1 Dovetail finder scope bracket
1 Equatorial mount
3 Tripod legs
1 Counterweight shaft
1 Counterweight
1 Tripod accessory tray
1 Accessory tray bracket
2 Slow‑motion control cables
1 1/4"‑20 adapter
Welcome to a new world of adventure. Your new StarMax 90mm EQ is designed for high‑resolution
observing of astronomical objects, and can also be used for terrestrial exploration. With its precision
optics and equatorial mount, you’ll be able to locate and enjoy hundreds of fascinating celestial objects,
including the planets, Moon, and a variety of deep‑sky galaxies, nebulas, and star clusters.
If you have never owned a telescope before, we would like to welcome you to amateur astronomy. Take
some time to familiarize yourself with the night sky. Learn to recognize the patterns of stars in the major
constellations. With a little practice, a little patience, and a reasonably dark sky away from city lights,
you’ll find your telescope to be a never‑ending source of wonder, exploration, and relaxation.
These instructions will help you set up, properly use and care for your telescope. Please read them over
thoroughly before getting started.
Table of Contents
1. Unpacking............................................................................................................................... 3
2. Parts List................................................................................................................................. 3
3. Assembly ................................................................................................................................ 4
4. Getting Started........................................................................................................................ 5
5. Setting Up and Using the Equatorial Mount............................................................................ 6
6. Using Your Telescope—Astronomical Observing .................................................................... 9
7. Terrestrial Viewing................................................................................................................. 12
8. Photography.......................................................................................................................... 12
9. Care and Maintenance ......................................................................................................... 12
10. Specifications........................................................................................................................ 13
WARNING: Never look directly at the Sun
through your telescope or its finder scope—
even for an instant—without a professionally
made solar filter that completely covers the front
of the instrument, or permanent eye damage
could result. Young children should use this
telescope only with adult supervision.

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1 Soft carry case
3 Assembly tools (small wrench, Phillips head
screwdriver, triangular assembly tool)
3 Leg attachment screws
3 Leg lock knobs
3. Assembly
1. Lay the equatorial mount on its side. Attach the tripod
legs, one at a time, to the base of the mount by sliding a
tripod leg attachment screw through the top of a leg and
through the holes in the base of the mount. The washers
should be on the outside of the tripod legs. Secure the
wing nuts finger‑tight. Note that the accessory tray brack‑
et attachment point on each leg should face inward.
2. Install and tighten the leg lock knobs on the bottom
braces of the tripod legs. For now, keep the legs at their
shortest (fully retracted) length; you can extend them to a
more desirable length later, after the tripod is completely
assembled.
3. With the tripod legs now attached to the mount, stand
the tripod upright (be careful!) and spread the legs apart
enough to connect each end of the accessory tray brack‑
et to the attachment point on each leg. Use the screw and
lock nut that come installed in each attachment point to
do this. First, remove the screw using the supplied screw‑
driver and triangular assembly tool; hold the lock nut
with the triangular assembly tool while turning the screw
with the screwdriver. Then, line up one of the ends of the
bracket with the attachment point and reinstall the screw.
4. Now, with the accessory tray bracket attached, spread the
tripod legs apart as far as they will go, until the bracket
is taut. Connect the accessory tray to the accessory tray
bracket with the three wing screws already installed in the
tray. This is done by pushing the wing screws up through
the holes in the accessory tray bracket and threading
them into the holes in the accessory tray.
5. Tighten the screws at the tops of the tripod legs, so the
legs are securely fastened to the mount. Use the provided
screwdriver and your fingers to do this.
6. Orient the equatorial mount as it appears in Figure 2, at
a latitude of about 40°, i.e., so the pointer next to the lati‑
tude scale (located directly above the latitude lock t‑bolt)
is pointing to the hash mark at “40.” To do this, loosen
Figure 2
Right ascension setting circle
Declination
slow motion control
Latitude scale
Latitude adjusting T‑Bolt
Latitude locking T‑Bolt
Declination lock knob
(not shown)
Declination setting circle
Right ascension
lock knob
Right Ascension slow
motion control
Declination
(Dec.) axis
Right ascension
(R.A.) axis

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the latitude lock t‑bolt, and turn the latitude adjustment
t‑bolt until the pointer and the “40” line up. Then retighten
the latitude lock t‑bolt. The declination (Dec.) and right
ascension (R.A.) axes may need re‑positioning (rotation)
as well. Be sure to loosen the R.A. and Dec. lock knobs
before doing this. Retighten the R.A. and Dec. lock knobs
once the equatorial mount is properly oriented.
7. Thread the counterweight shaft into the equatorial mount
at the base of the declination axis until tight.
8. Remove the screw and washer on the bottom of the coun‑
terweight shaft and slide the counterweight onto the shaft.
Make sure the counterweight lock knobs are adequately
loosened to allow the counterweight shaft to pass through
the hole. Position the counterweight about halfway up the
shaft and tighten the lock knobs. Replace the screw and
washer on the counterweight shaft.
9. Attach the 1/4"‑20 adapter to the top of the equato‑
rial mount using the bolts and washers that come with
the adapter. Push the bolts, with washers attached, up
through the holes in the top of the mount and thread them
into the bottom of the adapter. Tighten the bolts securely
with the supplied wrench.
10. Connect the optical tube assembly to the 1/4"‑20 adapter
on the mount by threading the adapter’s shaft into the
hole in the optical tube’s mounting block. Orient the opti‑
cal tube so that it is parallel to the length of the adapter, as
it is in Figure 1. Tighten this connection firmly by rotating
the knurled thumb wheel on the adapter counter‑clock‑
wise.
11. Now attach the two slow‑motion cables to the R.A. and
Dec. slow‑motion shafts of the equatorial mount by posi‑
tioning the thumbscrew on the end of the cable over the
indented slot on the shaft, then tightening the thumb
screw. A cable can be attached to either end of the R.A.
shaft, whichever is most convenient for you. Use the
shorter cable for the R.A. shaft.
12. To place the finder scope in its bracket, first remove the
O‑ring from the finder scope bracket. Loosen the three
nylon thumbscrews on the bracket until the tips of the
screws are flush with the inside of the bracket. Insert the
objective end (the end without the rubber eyeguard) of
the finder scope into the bracket ring with the three nylon
thumbscrews. When the finder scope is through the sec‑
ond ring of the bracket and as far as it will go, push the
O‑Ring on the objective end of the finder scope and set it
about 1" down the finder scope tube. Then pull the finder
scope back gently until the O‑Ring seats itself on the ridge
inside the second ring of the finder scope bracket. Tighten
the three nylon screws equally until they are touching the
sides of the finder scope.
13. Insert the base of the finder scope bracket into the dovetail
holder on the optical tube. Lock the bracket into position
by tightening the knurled thumbscrew on the dovetail
holder.
14. Remove the cap from the eyepiece adapter on the rear of
the optical tube and insert the chrome barrel of the mirror
star diagonal. Secure the diagonal with the thumbscrews
on the eyepiece adapter.
15. Now, insert the chrome barrel of the 25mm eyepiece into
the star diagonal. Secure the eyepiece with the thumb‑
screws on the star diagonal.
The telescope system is now fully assembled. Keep the dust
cover over the front end of the telescope when it is not in use.
It is also a good idea to cover the eyepiece; use the cover cap
that came with it.
4. Getting Started
Balancing the Telescope
To insure smooth movement of the telescope on both axes of
motion (R.A. and Dec.) of the equatorial mount, it is impera‑
tive that the optical tube be properly balanced.
1. Keeping one hand on the telescope optical tube, loosen the
R.A. lock knob. Make sure the Dec. lock knob is locked. 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 3: Proper operation of the equatorial mount requires
balancing the telescope tube on the R.A. axis. (a) With the
R.A. lock knob released, slide the counterweight along the
counterweight shaft until it just counterbalances the tube. (b)
When you let go with both hands, the tube should not drift
up or down.
a.
b.

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2. Now loosen the counterweight lock knob and slide the
weight along the shaft until it exactly counterbalances the tele‑
scope (Figure 3a). That’s the point at which the shaft remains
horizontal even when you let go of the telescope with both
hands (Figure 3b).
3. Retighten the counterweight lock knob.
The telescope is now balanced on the R.A. axis. It is not nec‑
essary to balance the telescope on the Dec. axis, since the
optical tube’s mounting block is positioned so that the tele‑
scope will automatically be balanced on that axis. Now when
you loosen the lock knob on one or both axes of motion and
manually point the telescope, it should move without resis‑
tance and should not drift from where you point it.
Focusing the Telescope
Point the telescope so the front end is aimed in the general
direction of an object at least 1/4‑mile away. Now, with your
fingers, slowly rotate the focusing knob until the object comes
into sharp focus. Go a little bit beyond sharp focus until the
image just starts to blur again, then reverse the rotation of the
knob, just to make sure you’ve hit the exact focus point.
If you have trouble focusing, rotate the focus knob counter‑
clockwise as far as it will go. Now look through the eyepiece
while slowly rotating the focus knob clockwise. You should
soon see the point at which focus is reached.
Do You Wear Eyeglasses?
If you wear eyeglasses, you may be able to keep them on
while you observe. In order to do this, your eyepiece must
have enough “eye relief" to allow you to see the entire field of
view with glasses on. You can try this by looking through the
eyepiece first with your glasses on and then with them off,
and see if the glasses restrict the view to only a portion of the
full field. If the glasses do restrict the field of view, you may be
able to observe with your glasses off by just refocusing the
telescope the needed amount.
If your eyes are astigmatic, images will probably appear the
best with glasses on. This is because a telescope’s focuser
can accommodate for nearsightedness or farsightedness,
but not astigmatism. If you have to wear your glasses while
observing and cannot see the entire field of view, you may
want to purchase additional eyepieces that have longer eye
relief.
Aligning the Finder Scope
The finder scope (Figure 4) must be aligned accurately with
the telescope for proper use. To align it, aim the main tele‑
scope in the general direction of an object at least 1/4‑mile
away, such as the top of a telephone pole, a chimney, etc. Do
this by first loosening the R.A. and Dec. lock knobs. Position
the telescope so the object appears in the eyepiece’s field of
view and then retighten the R.A. and Dec. lock knobs. Use
the slow‑motion control cables to center the object in the eye‑
piece.
Now, look in the finder scope. Is the object visible? Ideally, it
will be somewhere in the finder’s field of view. If it is not, some
coarse adjustments of the three black nylon finder scope
alignment thumbscrews will be needed to get the finder scope
roughly parallel to the main tube.
Note: The image in the telescope’s eyepiece will appear
inverted from left‑to‑right (mirror reversed), which is normal
for telescopes that utilize a star diagonal. The image in the
finder scope is oriented the same as the naked eye.
Use the three nylon thumbscrews to center the object on the
crosshairs of the finder scope. Then look again into the tele‑
scope’s eyepiece and see if the object is still centered there
as well. If it isn’t, repeat the entire process, making sure not
to move the main telescope while adjusting the alignment of
the finderscope.
The finder scope alignment needs to be checked before every
observing session. This can easily be done at night, before
viewing through the telescope. Choose any bright star or
planet, center the object in the telescope eyepiece, and then
adjust the finder scope’s alignment screws until the star or
planet is also centered on the finder’s crosshairs. The finder
scope is an invaluable tool for locating objects in the night sky;
its usage for this purpose will be discussed later, in detail.
Focusing the Finder Scope
If, when looking through the finder scope, the images appear
somewhat out of focus, you will need to refocus the finder
scope for your eyes. Turn the end of the finder scope with the
rubber eyeguard clockwise or counter‑clockwise as needed
to focus the finder scope on a distant object (1/4 mile away
or more). Precise focusing will be achieved by focusing the
finder scope on a bright star.
5. Setting Up and Using the
Equatorial Mount
When you look at the night sky, you no doubt have noticed
that the stars appear to move slowly from east to west over
time. That apparent motion is caused by the Earth’s rotation
(from west to east). An equatorial mount (Figure 2) is designed
Figure 4: The 6x20 Correct‑Image finder scope and bracket
Rubber
eyeguard
Nylon
thumbscrew
Finder scope
bracket
Nylon thumbscrew
O‑Ring
(not shown)
Objective
lens
Finder scope

7
to compensate for that motion, allowing you to easily “track"
the movement of astronomical objects, thereby keeping them
from drifting out of the telescope’s field of view while you’re
observing.
This is accomplished by slowly rotating the telescope on its
right ascension (R.A.) axis, using only the R.A. slow‑motion
cable. But first the R.A. axis of the mount must be aligned
with the Earth’s rotational (polar) axis ‑ a process called polar
alignment.
Polar Alignment
For Northern Hemisphere observers, approximate polar
alignment is achieved by pointing the mount’s R.A. axis at the
North Star, or Polaris. It lies within 1° 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 find Polaris in the sky, look north and locate the pattern
of the Big Dipper (Figure 5). The two stars at the end of the
“bowl" of the Big Dipper point right to Polaris.
Observers in the Southern Hemisphere aren’t so fortunate to
have a bright star so near the south celestial pole (SCP). The
star Sigma Octantis lies about 1° 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. Loosen the latitude lock t‑bolt. Turn the latitude adjust‑
ment t‑bolt and tilt the mount until the pointer on the
latitude scale is set at the latitude of your observing site. If
you don’t know your latitude, consult a geographical atlas
to find it. For example, if your latitude is 35° North, set
the pointer to 35. Then retighten the latitude lock t‑bolt.
The latitude setting should not have to be adjusted again
unless you move to a different viewing location some dis‑
tance away.
3. Loosen the Dec. lock knob and rotate the telescope opti‑
cal tube until it is parallel with the R.A. axis, as it is in
Figure 1. The pointer on the Dec. setting circle should
read 90°. Retighten the Dec. lock lever.
4. Loosen the azimuth lock knob at the base of the equa‑
torial mount and rotate the mount so the telescope tube
(and R.A. axis) points roughly at Polaris. If you cannot see
Polaris directly from your observing site, consult a com‑
pass and rotate the mount so the telescope points North.
Retighten the azimuth lock knob.
The equatorial mount is now polar aligned for casual observ‑
ing. More precise polar alignment is recommended for
astrophotography.
From this point on in your observing session, you should not
make any further adjustments in the azimuth or the latitude
of the mount, nor should you move the tripod. Doing so will
undo the polar alignment. The telescope should be moved
only about its R.A. and Dec. axes.
Use of the R.A. and Dec. Slow-Motion Control
Cables
The R.A. and Dec. slow‑motion control cables allow fine
adjustment of the telescope’s position to center objects within
the field of view. Before you can use the cables, you must
manually “slew" the mount to point the telescope in the vicini‑
ty of the desired target. Do this by loosening the R.A. and Dec.
lock knobs and moving the telescope about the mount’s R.A.
and Dec. axes. Once the telescope is pointed somewhere
close to the object to be viewed, retighten the mount’s R.A.
and Dec. lock knobs.
The object should now be visible somewhere in the tele‑
scope’s finder scope. If it isn’t, use the slow‑motion controls
to scan the surrounding area of sky. When the object is visible
in the finder scope, use the slow‑motion controls to center it.
Now, look in the telescope’s eyepiece. If the finder scope is
properly aligned, the object should be visible somewhere in
the field of view. Once the object is visible in the eyepiece, use
the slow‑motion controls to center it in the field of view.
The Dec. slow‑motion control cable can move the telescope a
maximum of 25°. This is because the Dec. slow‑motion mech‑
anism has a limited range of mechanical travel. (The R.A.
slow‑motion mechanism has no limit to its amount of travel).
If you can no longer rotate the Dec. control cable in a desired
direction, you have reached the end of travel, and the slow‑
motion mechanism must be reset. This is done by first rotating
the control cable several turns in the opposite direction from
which it was originally being turned. Then, manually slew the
telescope closer to the object you wish to observe (remember
to first loosen the Dec. lock knob). You should now be able to
use the Dec. slow‑motion control cable again to fine adjust
the telescope’s position.
Figure 5. To find Polaris in the night sky, look north and find
the Big Dipper. Extend an imaginary line from the two "Pointer
Stars" in the bowl of the Big Dipper. Go about five times the
distance between those stars and you'll reach Polaris, which
lies within 1° of the north celestial pole (NCP).
Big Dipper
(in Ursa Major)
Little Dipper
(in Ursa Minor)
N.C.P.
Pointer
Stars
Polaris

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Tracking Celestial Objects
When you observe a celestial object through the telescope,
you’ll see it drift slowly across the field of view. To keep it in
the field, if your equatorial mount is polar aligned, just turn
the R.A. slow‑motion control cable clockwise. The Dec. slow‑
motion control cable is not needed for tracking. Objects will
appear to move faster at higher magnifications, because
the field of view is narrower.
Optional Motor Drives for Automatic Tracking
An optional DC motor 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 field of view with‑
out any manual adjustment of the R.A. slow‑motion control
cable.
Understanding the Setting Circles
The setting circles on an equatorial mount enable you to
locate celestial objects by their “celestial coordinates".
Every object resides in a specific location on the “celestial
sphere". That location is denoted by two numbers: its right
ascension (R.A.) and declination (Dec.). In the same way,
every location on Earth can be described by its longitude
and latitude. R.A. is similar to longitude on Earth, and Dec.
is similar to latitude. The R.A. and Dec. values for celestial
objects can be found in any star atlas or star catalog.
The mount’s R.A. setting circle is scaled in hours, from 1
through 24, with small hash 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 small hash mark representing 2.5°.
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 celes‑
tial 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 listed in a star
atlas will look like this:
R.A. 5h 35.4m Dec. ‑5° 27'
That’s 5 hours and 35.4 minutes in right ascension, and ‑5
degrees and 27 arc‑minutes in declination (there are 60
arc‑minutes in 1 degree of declination).
Before you can use the setting circles to locate objects,
the mount must be well polar aligned, and the R.A. setting
circle must be calibrated. The Dec. setting circle has been
permanently calibrated at the factory, and should read 90°
whenever the telescope optical tube is parallel with the
R.A. axis.
Calibrating the Right Ascension Setting Circle
1. Identify a bright star 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 coordi‑
nates you know. Lock the R.A. and Dec. lock knobs.
Center the star in the telescope’s field of view with the
slow‑motion control cables.
4. Rotate the setting circle until the metal arrow indi‑
cates the R.A. coordinate listed in the star atlas for the
object.
Finding Objects With the Setting Circles
Now that both setting circles are calibrated, look up in a
star atlas the coordinates of an object you wish to view.
1. Loosen the Dec. lock knob and rotate the telescope until
the Dec. value from the star atlas matches the reading on
the Dec. setting circle. Remember that values of the Dec.
setting circle are positive when the telescope is pointing
north of the celestial equator (Dec.= 0°), and negative
when the telescope is pointing south of the celestial equa‑
tor. Retighten the lock knob.
2. Loosen the R.A. lock knob and rotate the telescope until
the R.A. value from the star atlas matches the reading on
the R.A. setting circle. Remember to use the upper set
of numbers on the R.A. setting circle. Retighten the lock
knob.
Most setting circles are not accurate enough to put an
object dead‑center in the telescope’s eyepiece, but they
should place the object somewhere within the field of view
of the finder scope, assuming the equatorial mount is accu‑
rately polar aligned. Use the slow‑motion controls to center
the object in the finder scope, and it should appear in the
telescope’s field of view.
The R.A. setting circle must be re‑calibrated every time
you wish to locate a new object. Do so by calibrating the
setting circle for the centered object before moving on to
the next one.
Confused About Pointing the Telescope?
Beginners occasionally experience some confusion about
how to point the telescope overhead or in other directions.
In Figure 1 the telescope is pointed north, as it would be
during polar alignment. The counterweight shaft is oriented
downward. But it will not look like that when the telescope
is pointed in other directions. Let’s say you want to view an
object that is directly overhead, at the zenith. How do you
do it?
One thing you DO NOT do is make any adjustment to the
latitude adjustment t‑bolt. That will nullify the mount’s polar
alignment. Remember, once the mount is polar aligned, the
telescope should be moved only on the R.A. and Dec. axes.
To point the scope overhead, first loosen the R.A. lock knob
and rotate the telescope on the R.A. axis until the coun‑
terweight shaft is horizontal (parallel to the ground). Then
loosen the Dec. lock knob and rotate the telescope until it is
pointing straight overhead. The counterweight shaft is still
horizontal. Then retighten both lock knobs.

9
Similarly, to point the telescope directly south, the counter‑
weight shaft should again be horizontal. Then you simply
rotate the scope on the Dec. axis until it points in the south
direction.
What if you need to aim the telescope directly north, but
at an object that is nearer to the horizon than Polaris?
You can’t do it with the counterweight down as pictured in
Figure 1. Again, you have to rotate the scope in R.A. so the
counterweight shaft is positioned horizontally. Then rotate
the scope in Dec. so it points to where you want it near the
horizon.
To point the telescope to the east or west, or in other
directions, you rotate the telescope on its R.A. and Dec.
axes. Depending on the altitude of the object you want to
observe, the counterweight shaft will be oriented some‑
where between vertical and horizontal.
Figure 6 illustrates how the telescope will look pointed at
the four cardinal directions ‑ north, south, east, and west
The key things to remember when pointing the telescope is
that a) you only move it in R.A. and Dec., 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!
6. Using Your Telescope—
Astronomical Observing
Choosing an Observing Site
When selecting a location for observing, get as far away as
possible from direct artificial light such as 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 tempera‑
ture 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 significantly from night to night.
“Seeing" refers to the steadiness of the Earth’s atmosphere at
a given time. In conditions of poor seeing, atmospheric turbu‑
lence causes objects viewed through the telescope to “boil".
If, when you look up at the sky with just your eyes, the stars
are twinkling noticeably, the seeing is bad and you will be lim‑
ited to viewing with low powers (bad seeing affects images at
high powers more severely). Planetary observing may also be
poor.
In conditions of good seeing, star twinkling is minimal and
images appear steady in the eyepiece. Seeing is best over‑
head, 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 “trans‑
parency"—air free of moisture, smoke, and dust. All tend to
scatter light, which reduces an object’s brightness.Transparency
is judged by the magnitude of the faintest stars you can see with
the unaided eye (6th magnitude or fainter is desirable).
Cooling the Telescope
All optical instruments need time to reach “thermal equilibri‑
um". The bigger the instrument and the larger the temperature
change, the more time is needed. Allow at least 30 minutes
for your telescope to cool to the temperature outdoors. In very
cold climates (below freezing), it is essential to store the tele‑
scope as cold as possible. If it has to adjust to more than a
40° temperature change, allow at least one hour.
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, galax‑
ies, 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‑
Figure 6: This illustration shows 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 tube has been moved on the R.A. and Dec. axes.
a. b.
c. d.

10
adapted, more stars will glimmer into view and you’ll be able to
see fainter details in objects you view in your telescope.
To see what you’re doing in the darkness, use a red‑filtered
flashlight rather than a white light. Red light does not spoil
your eyes’ dark adaptation like white light does. A flashlight
with a red LED light is ideal, or you can cover the front of a
regular incandescent flashlight with red cellophane or paper.
Beware, too, that nearby porch and streetlights and car head‑
lights will ruin your night vision.
Eyepiece Selection
By using eyepieces of varying focal lengths, it is possible to
attain many magnifications with the StarMax 90mm EQ. The
telescope comes with one high‑quality 25mm Sirius Plössl,
which gives a magnification of 50x. Other eyepieces can be
used to achieve higher or lower powers. It is quite common for
an observer to own five or more eyepieces to access a wide
range of magnifications.This allows the observer to choose the
best eyepiece to use depending on the object being viewed.
To calculate the magnification, or power, of a telescope and
eyepiece combination, simply divide the focal length of the
telescope by the focal length of the eyepiece:
Magnification =
(focal length of telescope) ÷ (focal length of eyepiece)
For example, the StarMax 90mm EQ, which has a focal length
of 1250mm, used in combination with the 25mm eyepiece,
yields a power of
1250mm ÷ 25mm = 50x
Every telescope has a useful limit of power of about 2x per
mm of aperture (about 180x for the StarMax 90mm EQ).
Claims of higher power by some telescope manufacturers are
a misleading advertising gimmick and should be dismissed.
Keep in mind that at higher powers, an image will always be
dimmer and less sharp (this is a fundamental law of optics).
The steadiness of the air (the “seeing") will also limit how
much magnification an image can tolerate.
Whatever you choose to view, always start by inserting your
lowest‑power (longest focal length) eyepiece to locate and
center the object. Low magnification yields a wide field of
view, which shows a larger area of sky in the eyepiece. This
makes acquiring and centering an object much easier. If you
try to find and center objects with high power (narrow field of
view), it’s like trying to find a needle in a haystack!
Once you’ve centered the object in the eyepiece, you can
switch to higher magnification (shorter focal length eyepiece),
if you wish. This is especially recommended for small and
bright objects, like planets and double stars. The Moon also
takes higher magnifications well.
Deep‑sky objects, however, typically look better at medium
or low magnifications. This is because many of them are
quite faint, yet have some extent (apparent width). Deep‑sky
objects will often disappear at higher magnifications, since
greater magnification inherently yields dimmer images. This
is not the case for all deep‑sky objects, however. Many galax‑
ies are quite small, yet are somewhat bright, so higher power
may show more detail.
The best rule of thumb with eyepiece selection is to start
with a low power, wide field, and then work your way up in
magnification. If the object looks better, try an even higher
magnification. If the object looks worse, then back off the
magnification a little by using a lower‑power eyepiece.
Rotating the Diagonal
When looking at objects in different areas of the night sky,
the eyepiece may become positioned so that is uncomfort‑
able or impossible to look through. If the eyepiece is in an
undesirable position, the diagonal can be rotated in order to
provide a more comfortable viewing angle. First, loosen the
thumb screws on the eyepiece adapter, but make sure to hold
the diagonal in place so that it won’t fall to the ground. Also,
secure the eyepiece in the diagonal so that it won’t fall out
when rotating the diagonal. Retighten the thumb screws on
the eyepiece adapter once the diagonal has been rotated to
an appropriate position.
Objects to Observe
Now that you are all set up and ready to go, one critical deci‑
sion must be made: what to look at?
A. The Moon
With its rocky surface, the Moon is one of the easiest and most
interesting targets to view with your telescope. Lunar craters,
marias, and even mountain ranges can all be clearly seen
from a distance of 238,000 miles away! With its ever‑chang‑
ing phases, you’ll get a new view of the Moon every night. The
best time to observe our one and only natural satellite is dur‑
ing 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 filter to dim the Moon when it is very
bright. It simply threads onto the bottom of the eyepieces (you
must first remove the eyepiece from the focuser to attach a fil‑
ter). You’ll find that the Moon filter improves viewing comfort,
and also helps to bring out subtle features on the lunar sur‑
face.
B. The Sun
You can change your nighttime telescope into a daytime Sun
viewer by installing an optional full‑aperture solar filter over
the front opening of the StarMax 90mm EQ. The primary
attraction is sunspots, which change shape, appearance, and
location daily. Sunspots are directly related to magnetic activity
in the Sun. Many observers like to make drawings of sunspots
to monitor how the Sun is changing from day to day.
Important Note: Do not look at the Sun with any optical
instrument without a professionally made solar filter, or
permanent eye damage could result.