Orion 90mm f/10.1 refractor Manual

IN 310 Rev. B 02/09
Customer Support [phone]
E-mail: [email protected]
Corporate Offices [phone]
89 Hangar Way, Watsonville, CA 95076
INSTRUCTION MANUAL
Providing Exceptional Consumer Optical Products Since 1975
Orion®90mm
f/10.1 Refractor
#9190

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WARNING: Never look at the sun with your
telescope (or even with just your eyes) without a
professionallymadesolarfilter.Permanenteyedamage
or blindness could result. Young children should use
this telescope only with adult supervision.
Avoid using the type of solar filter that screws into
an eyepiece. They are susceptible to cracking under
the intense heat that builds up near the focus point,
and could cause severe retinal damage. Use only
the type of solar filter that covers the front of the
telescope. Also, be sure to leave the cover caps on
the finder scope when solar observing. Better yet,
remove the finder scope altogether when viewing
the sun.
Figure 1. The 90mm f/10.1 refractor.
Dew/Glare shield
Welcome to a new world of adventure! Your Orion 90mm f/10.1 Refractor is a fine-quality instrument designed for both daytime
terrestrial viewing and nighttime stargazing. This versatile scope will provide many hours of enjoyment for the whole family.
These instructions will help you set up and properly use and care for your telescope. Please read them over thoroughly before
getting started.
Parts List
Qty. Description
1 Optical tube assembly
1 25mm Sirius Plössl eyepiece (36x)
1 10mm Sirius Plössl eyepiece (91x)
1 45° Correct-image diagonal, 1.25"
1 6x26 Correct-image finder scope
1 Finderscope bracket with O-ring
1 Dovetail tube ring mounting plate
2 Tube rings with mounting hardware
1 Objective lens cap
Tube rings
Finder scope
bracket
Finder scope
Eyepiece (25mm)
Correct-image diagonal
Focus wheels
Dovetail tube ring mounting plate

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Getting Started
The 90mm refractor comes nearly fully assembled from the
factory. The telescope’s optics have been installed and col-
limated, so you should not have to make any adjustments to
them. Open the box and inspect the contents to make sure
all of the items in the parts list are present.
Please keep the original shipping box. In the unlikely event
you should need to ship the telescope back to Orion for war-
ranty repair service, you should use the original packaging.
The box also makes a very good container for storing the
telescope when it is not in use.
Installing the Finder Scope
To place the finder scope in the finder scope bracket (Figure
2a.), first unthread the two black nylon thumbscrews until
the screw ends are flush with the inside diameter of the
bracket. Place the O-ring that comes on the base of the
bracket over the body of the finder scope until it seats into
the slot on the middle of the finder scope. Slide the eye-
piece end (narrow end) of the finder scope into the end of
the bracket’s cylinder opposite the adjustment screws while
pulling the chrome, spring-loaded tensioner on the bracket
with your fingers (Figure 2b.) Push the finder scope through
the bracket until the O-ring seats just inside the front open-
ing of the bracket’s cylinder. Now, release the tensioner and
tighten the two black nylon screws a couple of turns each to
secure the finder scope in place. Secure the bracket to the
dovetail mount on the optical tube with the knurled thumb-
screw on the dovetail mount.
Installing the Diagonal and Eyepiece
Insert the 45° correct-image diagonal into the focuser draw-
tube and secure it with the knurled thumbscrew on the
drawtube. Then insert the 25mm Sirius Plössl eyepiece into
the diagonal and secure it in place with the thumbscrews on
the diagonal. (Always loosen the thumbscrews before rotat-
ing or removing the diagonal or an eyepiece.)
Mounting the Telescope
The 90mm refractor can be easily mounted on altazimuth
mounts, like the Orion VersaGo, which utilize a dovetail hold-
er. Attach the included tube rings to the dovetail mounting
plate with the included hex head screws. Be sure to place a
lock washer and then a flat washer onto each screw before
attaching. Insert the screws (with washers) through the
holes in the plate and thread them into the base of the tube
rings (Figure 2c). Tightening the screws requires a 10mm
crescent wrench or an adjustable crescent wrench. Place
the optical tube into the open rings. Close the rings, and
use the silver clamping knob on each tube ring to secure
the telescope. The dovetail mounting plate now connected
to the 90mm refractor connects directly to the VersaGo’s
dovetail holder.
The 90mm refractor can also be mounted on Orion equatorial
mounts using the dovetail mounting plate. Follow the previous
directions to couple the telescope to the mounting plate with
the tube rings.
An equatorial mount is desirable for astronomical viewing
as it allows easy manual and/or motorized tracking of celes-
Figure 2b. Inserting the finder scope into the finder scope bracket.
Figure 2c. Attaching the dovetail mounting plate.
Dovetail
mounting
plate
Hex head screws
Tube ring clamping
knobs
Figure 2a. The 6x26 correct-image finder scope and bracket
Focus
lock-ring
Alignment thumbscrews
Tensioner
Piggyback camera adapter
Flat washer
Lock washer

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tial objects as the Earth rotates. Setting circles on equato-
rial mounts also enable you to locate objects by their celestial
coordinates (right ascension and declination), which can be
found in many observing books and star atlases.
Note: If you are using an Orion EQ-2 equatorial mount, the
dovetail mounting plate is not needed for attaching the tele-
scope. Simply mount the telescope to your EQ-2 mount by
attaching the tube rings directly to the mount head and then
placing the telescope into the tube rings. Be sure to tighten
the silver tube ring clamping knobs to secure the telescope.
Focusing
The 90mm refractor is equipped with a precision rack-and-
pinion focuser. When you first look in the eyepiece, the
image you see may be fuzzy, or out of focus. If so, gently
turn one of the focusing wheels with your fingers until the
image becomes sharp. You will have to readjust the focus
when aiming at subjects of varying distances, or after
changing eyepieces. Make sure the focus lock thumbscrew
is loosened before focusing (see Figure 3). After focusing,
you can tighten it to lock the telescope’s focus into place.
Do You Wear Eyeglasses?
If you wear eyeglasses, you may be able to keep them on
while you observe, if your eyepieces have enough “eye
relief” to allow you to see the whole field of view. You can
find out by looking through the eyepiece first with your
glasses on and then with them off, and see if the glasses
restrict the view to only a portion of the full field. If they do,
you can easily observe with your glasses off by just refocus-
ing the telescope the needed amount.
Aligning the Finder Scope
The 90mm refractor comes with a 6x26 correct-image finder
scope. (The 6x means six-times magnification, and the 26
indicates a 26mm aperture.) The finder scope makes it
easier to locate the subject you want to observe in the tele-
scope, because the finder scope has a much wider field of
view. Unlike most finder scopes, images viewed in the cor-
rect-image finder scope will appear properly oriented (same
as the naked eye) which makes finding objects even easier.
Focusing the Finder Scope
If, when looking through the finder scope, you notice that
the images appear somewhat out of focus, you will need to
refocus the finder scope for your eyes. First loosen the lock
ring located behind the objective lens cell on the body of the
finder scope (see Figure 2a). Back the lock ring off by a few
turns, for now. Refocus the finder scope on a distant object
by threading the objective lens cell in or out of the finder
scope body. Precise focusing will be achieved by focusing the
finder scope on a bright star. Once the image appears sharp,
retighten the lock ring behind the objective lens cell. The
finder scope’s focus should not need to be adjusted again.
Terrestrial Viewing
Many people enjoy using their telescope to view objects
such as boats, birds and wildlife. The 90mm refractor is an
excellent instrument for observing during the daylight hours.
For terrestrial applications, we recommend mounting the
90mm refractor on an altazimuth-style camera tripod or
telescope mount such as the Orion VersaGo, which allow
simple vertical (altitude) and horizontal (azimuth) motions.
Astronomical Viewing
The 90mm refractor excels for astronomical observation.
Its unobstructed 90mm aperture and short 910mm focal
length (f/10.1) provide bright, expansive views of star fields
and celestial objects residing within our solar system and
beyond.
Once the Sun sets, there are literally thousands of objects in
the night sky that can be inspected more closely. For astro-
nomical usage, we recommend a 90° mirror star diagonal
instead of the 45° correct-image diagonal that comes with
the telescope. The viewing angle provided by a star diagonal
is more comfortable for looking up. Keep in mind when using
a star diagonal, the image in the eyepiece will appear back-
wards (inverted left-to-right).
For casual stargazing, an altazimuth mount mount will do
the job just fine. But an equatorial mount is designed to
make it easier to manually “track” the motion of celestial
objects (due to the rotation of the Earth) with just one slow-
motion cable. Furthermore, with an equatorial mount you
can add an optional motor drive to track the stars automati-
cally—a great convenience.
When selecting a location for nighttime stargazing, make
it as far away from city lights as possible. Light-polluted
skies greatly reduce what can be seen with the telescope.
Also, give your eyes at least 20 minutes to dark-adapt to the
night sky. You’ll be surprised at how many more stars you
will see! Use a red flashlight to see what you’re doing at the
telescope, or to read star charts. Red light will not spoil your
dark-adapted night vision as readily as white light will.
To find celestial objects with your telescope, you first need
to become reasonably familiar with the night sky. Unless you
know how to recognize the constellation Orion, for instance,
Figure 3. The 90mm refractor with 35mm SLR camera attached.
Focus lock thumbscrew
T-ring

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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 vis-
ible in the sky on a given night.
A good star chart or atlas can come in handy for helping
locate interesting objects among the dizzying multitude
of stars overhead. Except for the Moon and the brighter
planets, it is pretty time-consuming and frustrating to hunt
for objects randomly, without knowing where to look. It is
best to have specific targets in mind before you begin look-
ing through the eyepiece.
Observing the Night Sky
The 90mm refractor is designed to provide excellent views
of our solar system as well as many bright deep sky objects.
You’ll see Galaxies, nebulae, star clusters, the Moon, Sun
and planets like never before. The following paragraphs will
help you get the most out of an observing session.
A. The Moon
The Moon, with its rocky, cratered surface, is one of the
easiest and most interesting subjects to observe with your
telescope. The myriad craters, rilles, and jagged moun-
tain formations offer endless fascination. The best time to
observe the Moon is during a partial phase, that is, when
the Moon is not full. During partial phases, shadows cast by
crater walls and mountain peaks along the border between
the dark and light portions of the lunar disk highlight the
surface relief. A full Moon is too bright and devoid of surface
shadows to yield a pleasing view. Try using a Moon filter to
dim the Moon when it is too bright; it simply threads onto the
bottom of the eyepiece.
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 90mm refractor. The primary attrac-
tion is sunspots, which change shape, appearance, and loca-
tion 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 per-
manent eye damage could result. Also, remember to cover
or remove the finder scope.
C. The Planets
The planets don’t stay put like stars do (planets don’t have
fixed R.A. and Dec. coordinates), so you will have to refer to
Sky Calendar at our website, www.OrionTelescope.com, or
to charts published monthly in Astronomy, Sky & Telescope,
or other astronomy references to locate them. Venus, Mars,
Jupiter, and Saturn are the brightest objects in the sky after
the Sun and the Moon. All four of these planets are not nor-
mally visible in the sky at one time, but chances are one or
two of them will be.
D. Stars
Stars will appear like twinkling points of light in the tele-
scope. Even the largest telescopes cannot magnify stars
to appear as anything more than points of light! You can,
however, enjoy the different colors of the stars and locate
many pretty double and multiple stars. The famous “Double-
Double” in the constellation Lyra and the gorgeous two-color
double star Albireo in Cygnus are favorites. Defocusing the
image of a star slightly can help bring out its color.
E. Deep-Sky Objects
Under dark skies, you can observe a number of brighter
deep-sky objects with your 90mm refractor, including gas-
eous nebulas, open and globular star clusters, and the
brighter galaxies. Most deep-sky objects are very faint, so it
is important that you find an observing site well away from
light pollution. Take plenty of time to let your eyes adjust
to the darkness. Don’t expect these objects to appear like
the photographs you see in books and magazines; most
will look like dim gray “ghosts.” (Our eyes are not sensitive
enough to see color in deep-sky objects except in few of the
brightest ones.) But as you become more experienced and
your observing skills improve, you will be able to coax out
more and more intricate details.
Calculating Magnification
(Power)
It is desirable to have a range of eyepieces of different focal
lengths, to allow viewing over a range of magnifications. To
calculate the magnification, or power, of a telescope, simply
divide the focal length of the telescope by the focal length of
the eyepiece:
Telescope F.L. ÷ Eyepiece F.L.=Magnification
For example, the 90mm refractor, which has a focal length of
910mm, used in combination with the supplied 25mm Sirius
Plössl eyepiece, yields a magnification of
910 ÷ 25 = 36x
Every telescope has a useful limit of magnification of about
45x-60x per inch of aperture, which is 159x-212x for the
90mm refractor. 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”) can also limit how much magnification an image
can tolerate.
Always start viewing with your lowest-power (longest focal
length) eyepiece in the telescope. After you have located
and looked at the object with it, you can try switching to a
higher-power eyepiece, like the supplied 10mm Sirius Plössl
eyepiece, to ferret out more detail. If the image you see is not
crisp and steady, reduce the magnification by switching to a
longer-focal-length eyepiece. As a general rule, a small but
well-resolved image will show more detail and provide a more
enjoyable view than a dim and fuzzy, overmagnified image.

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Photography with the 90mm Refractor
With an optional camera adapter, the 90mm refractor
becomes a 910mm f/10.1 telephoto lens for a single-lens
reflex camera. For long-distance terrestrial or astronomical
photography, you need only a T-ring for your particular cam-
era model. The T-ring attaches to your particular camera
model and threads onto the refractor’s focuser drawtube,
coupling the camera body to the telescope (Figure 3).
Use the camera’s viewfinder to frame the picture. Use the
telescope’s focuser to focus the image. Tighten the focus
lock thumbscrew on the telescope’s focuser to make sure
the camera does not slip out of focus.
You may want to consider using a remote shutter release
instead of the shutter release on the camera. Touching the
camera can vibrate the system and blur the resulting photo-
graphic image. Also, be sure to use a solid tripod.
Care & Maintenance
Give your telescope reasonable care and it will last a life-
time. Store it indoors or in a dry garage. Do not leave the
telescope outside except when using it. The optical tube is
aluminum and has a smooth painted surface that should
resist scratches and smudges. If a scratch does appear
on the tube, it will not harm the telescope. If you wish, you
can apply some white auto touch-up paint to the scratch.
Smudges on the tube can be wiped off with standard house-
hold cleaning fluid.
Any quality optical lens tissue and cleaning fluid specifically
designed for multi-coated optics can be used to clean the
telescope’s objective lens as well as the lenses of the eye-
pieces and finder scope. Never use regular glass cleaner or
cleaning fluid designed for eyeglasses. Before cleaning with
fluid and tissue, blow any loose particles off the lens with
a blower bulb or compressed air, or lightly brush the lens
with a soft camel hair brush. Apply some cleaning fluid to
a tissue, never directly on the optics. Wipe the lens gently
in a circular motion, then remove any excess fluid with a
fresh lens tissue. Oily fingerprints and smudges may be
removed using this method. Use caution; rubbing too hard
may scratch the lens! On larger lenses, clean only a small
area at a time, using a fresh lens tissue on each area. Never
reuse tissues.
Specifications
Objective lens: Achromatic doublet, air spaced
Objective lens coatings: Fully coated with multi-coatings
Optical tube: Seamless aluminum
Aperture: 90mm (3.5”)
Focal length: 910mm
Focal ratio: f/10.1
Focuser: Rack-and-pinion, 1.25” accepts
camera T-ring
Optical tube length: 35.5”
Weight of
optical tube assembly: 6lbs. 3oz.
Mounting provision: Dovetail tube ring mounting
plate, attaches to telescope via
tube rings (included)
Finder scope: 6x magnification, 26mm effective
aperture, achromatic, crosshairs,
provides image orientation same
as the naked eye
Eyepieces: 25mm and 10mm Sirius Plössls,
fully coated with multi-coatings,
1.25” barrel diameter, threaded
for Orion filters
Diagonal: 45° correct-image, 1.25” barrel
diameter

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One-Year Limited Warranty
The Orion 90mm f/10.1 Refractor is warranted against defects in materials or workmanship for a
period of one year from the date of purchase. This warranty is for the benefit of the original retail
purchaser only. During this warranty period Orion Telescopes & Binoculars will repair or replace, at
Orion’s option, any warranted instrument that proves to be defective, provided it is returned post-
age paid to: Orion Warranty Repair, 89 Hangar Way, Watsonville, CA 95076. Proof of purchase
(such as a copy of the original receipt) is required.
This warranty does not apply if, in Orion’s judgment, the instrument has been abused, mishandled, or
modified, nor does it apply to normal wear and tear. This warranty gives you specific legal rights, and you
may also have other rights, which vary from state to state. For further warranty service information, con-
tact: Customer Service Department, Orion Telescopes & Binoculars, 89 Hangar Way, Watsonville, CA
95076; [phone].