ORION TELESCOPES & BINOCULARS EON ED90T User manual

Orion
®
EON
™
ED90T
90mm ED Triplet Carbon Fiber
Apochromatic Refractor
#10386
IN 671 01/22
INSTRUCTION MANUAL
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Copyright © 2022 Orion® Telescopes & Binoculars.All Rights Reserved. No part of this product instruction or any of its contents
may be reproduced, copied, modied or adapted, without the prior written consent of Orion® Telescopes & Binoculars.
AN EMPLOYEE-OWNED COMPANY
Congratulations on your purchase of an Orion® EON ED90T CF 90mm ED Triplet Carbon
Fiber Apochromatic Refractor! This premium telescope excels for both visual observing and
astrophotography. It is designed with high quality precision ED optics and superior mechani-
cal construction. The optical tube is made from lightweight, thermally stable carbon ber
material, which makes the telescope lighter and less prone to rapid expansion and contrac-
tion with changes in temperature.The sturdy 2.5" dual-speed (10:1) rack-and-pinion focuser
will rigidly support substantial imaging or visual equipment loads and provide smooth, back-
lash-free focusing. The extra-low dispersion, or “ED,” optics offer outstanding color correc-
tion. These instructions will help you set up and use your telescope.

2
WARNING: Do NOT look at the Sun without a
professionally made solar lter on the telescope;
serious eye damage may result if you look at the
Sun with any unltered optical instrument. Do not
leave the telescope unsupervised around children.
Always cover the lenses when leaving the telescope
in direct sunlight.
Contents
1. Parts List 2
2. Features and Functions 2
3. Operating the EON ED90T CF 4
4. Care & Maintenance 6
6. Specications 6
1. Parts List
• EON ED90T CF optical tube assembly
• Aluminum objective cap
• Protective cap for ne focus knob
• 2"-to-1.25" twist-tight adapter
• Tube ring assembly with dovetail mounting bar and handle
• Thumbscrew for dew shield
• Hard carrying case
The EON ED90T CF apochromatic refractor comes fully assem-
bled from the factory. The telescope’s optics have been assem-
bled and precisely collimated at the factory, so they should not
require any adjustments. Please keep the original shipping box.
In the unlikely event that you need to ship the telescope back
to Orion for warranty repair service, you should use the original
packaging.
2. Features and Functions
The EON ED90T CF apochromatic refractor has premium
features designed to maximize the performance of the scope
and its convenience of use. Please refer to Figure 1 to become
familiar with the telescope’s features.
Optics
The EON ED90T CF incorporates an air-spaced triplet lens
assembly, with one ED (extra-low dispersion) lens made from
FCD100 ED glass by Hoya of Japan. It is essentially equivalent
Figure 1. Features and components of the EON ED90T Carbon Fiber Apochromatic Refractor
Dovetail bar
2" accessory
collar
Focuser rotation collar
Finder scope shoe
Camera angle
adjuster
Handle
Fine focus knob
Tube rings
Coarse
focus knob
1.25" adapter
Retractable
dew shield
Clamp knobs

3
to FPL-53 glass manufactured by Ohara. FCD100 is an extremely
low dispersion optical glass equivalent to uorite (CaF2). It
provides advanced correction of chromatic aberration, which
results in sharper images both visually and photographically.
The ED90T CF’s lenses are fully multi-coated – meaning all air-
to-glass surfaces have multi-layer antireective coatings applied
– for maximum light transmission to the eyepiece or camera. In
addition, the lens edges are blackened before they are mounted
in the lens cell to prevent unwanted reections from affecting the
image quality.
Retractable Dew Shield
The dew shield of the EON ED90T CF is retractable, allowing
the telescope to become more compact for storage. With the
dew shield extended, the scope is 19.8" long; with the dew shield
retracted (and tube rings still attached), the length reduces to
18”. The dew shield’s primary purpose is to inhibit dew (water
condensation) from forming on the lens during cold and humid
nights. The dew shield is also useful for reducing glare from
unwanted outside lights.
The dew shield comes fully retracted in the carrying case. To
extend the dew shield, simply pull it forward until it stops. A
thumbscrew included (in a small plastic bag) with the telescope
should be threaded into the hole in the red collar just behind the
dew shield (Figure 2). The thumbscrew should be lightly tight-
ened once the dew shield is fully extended, then loosened when
you want to retract the dew shield.
Dual-Speed 2.5" Rack-and-Pinion Focuser
Focusing the EON ED90T CF is smooth and responsive, thanks
to the all-machined, 2.5" rack-and-pinion focuser (Figure 3). It
features a bias (diagonal) cut on the rack to provide exception-
ally smooth, backlash-free focus motion and excellent rigidity for
holding imaging trains.This rack-and-pinion design is superior to
Crayford designs because it minimizes focuser slip with heavier
loads and pointing high in the sky – critical when trying to obtain
precise and repeatable focus. In our tests this focuser held up to
19 lbs. without slippage.
The dual-speed focusing mechanism will keep your target object
crisp and sharp. For quick focusing, the two large focus knobs
provide a coarse focus. For more precise focusing, as needed
for applications such as high-power planetary observing and
imaging with a CCD or digital camera, the smaller focus knob
on the right side offers a 10:1 ne focus adjustment (10 turns of
the ne focus knob equals one turn of the coarse focus knob).
If you nd that the focusing motion is too stiff or if the drawtube
slips under the weight of your eyepiece or camera, you can make
adjustments to the focuser tension by using the focuser tension
thumbscrew located on the bottom side of the focuser (Figure
4). Make adjustments to this setscrew until the focuser motion
feels smooth and holds in place when you have obtained focus.
It may be necessary to make adjustments when the weight of
your accessories changes signicantly.
Twist-Tight Accessory Collars
The EON ED90T CF features a 2" twist-tight collar and a
1.25" twist-tight adapter (Figure 5). The twist-tight mechanism
replaces and is superior to conventional collars that utilize only a
thumbscrew to secure accessories to the focuser. The twist-tight
mechanism provides an extremely secure attachment with just a
twist of the large knurled collar. Both collars have a non-marring
Figure 2. Thread the thumbscrew included separately into
the hole in the collar behind the dew shield.
Figure 3. The 2.5" dual-speed focuser has a rotatable collar
as well as a Camera Angle Adjuster.
Focuser rotation
collar
Focuser rotation
lock knob
Camera angle
adjuster (CAA)
2" twist
tight
collar
1.25"
twist tight
collar
Locking
thumbscrew Coarse focus
knob
CAA lock
knob
Fine focus
knob

4
internal compression ring for securing a diagonal, eld attener,
camera adapter, or other accessories. To insert an accessory
into the collar, rst twist the collar counterclockwise to widen the
internal compression ring, then insert your 2" accessory into the
collar (or your 1.25" accessory into the 1.25" collar). Then just
twist the collar clockwise until it is tight.The 2" collar also has a
thumb screw to provide an added measure of security.
Engraved Millimeter Scale on Focuser Drawtube
The drawtube of the EON ED90T CF’s focuser features a laser-
engraved millimeter scale on top, which aids in providing repeat-
able focus. When precise focus is achieved, noting the value
on the scale where the drawtube meets the focuser housing
will allow you to return to approximately the same point, such
as when focusing the same camera in subsequent imaging
sessions. Using the scale can save time compared to nding
the focusing point “from scratch” each time.
Focuser Rotation and Camera Angle Adjustment
(CAA)
The focuser on the EON ED90T CF has two rotatable compo-
nents. First, the entire focuser can be rotated just behind the
tapered red collar where the focuser attaches to the optical tube
(see Figure 1). On that collar is a thumbscrew, which when tight-
ened locks the focuser in position and when loosened allows
the focuser to be rotated. Rotating the focuser will re-orient the
focus knobs to a position that may be more desirable, depend-
ing on your mount setup and what you’re observing or imaging.
For instance, this feature can allow you to keep the focus knobs
parallel to the ground no matter how your telescope is positioned.
Second, the Camera Angle Adjustment (CAA) is the grooved
collar just in front of the 2" accessory holder (Figure 1). It has
a knob that when loosened allows the collar to be rotated. The
CAA is useful for astrophotography by allowing the camera to be
rotated independent of the rest of the telescope in order to frame
a target object on the camera’s sensor.
Reaching Focus
Your EON ED90T CF apochromatic refractor must be used with
either a diagonal or extension tube in order for an eyepiece to
reach focus. We recommend using a 90° star diagonal (2" or
1.25") for visual use with an eyepiece. For astrophotography we
recommend using a 2" eld attener designed for short-focal-
length refractors, such as the Orion Field Flattener for Short
Refractors (#8893), or our 0.8x Focal Reducer (#8894), which
shortens the effective focal length and attens the eld. Even
premium triplet refractors such as the ED90T CF need correction
to provide a at eld so that stars are pinpoint sharp all the way
to the edge of the photographic frame. That’s just the nature of
triplet optics. Optical atteners are not needed or recommended
for visual use.
Finder Scope Compatibility
Adding an optional nder scope to the EON ED90T CF is easy.
The focuser is equipped with a dovetail nder scope shoe (see
Figure 1) that accepts any Orion nder scope or reex sight as
well as the Orion Dual Finder Scope bracket (#10145). Alter-
natively, the nder scope shoe can be used to mount a small
guide scope with a compatible bracket. Simply loosen the lock-
ing thumbscrew, slide your nder scope or guide scope in until it
is fully seated, then lock the thumbscrew back down.
3. Operating the EON
ED90T CF
The EON ED90T CF is a versatile telescope designed for both
high-performance imaging and wide-eld visual pursuits. Its fast
f/6 focal ratio and ample 90mm (3.5") ED optics make it an espe-
cially powerful instrument for imaging with dedicated astronomi-
cal cameras or DSLR and mirrorless cameras.
Now that you have become familiar with the different features
and functions of the telescope, you are ready to begin using your
Figure 4. The underside of the focuser features a focuser
tension thumbscrew.
Figure 5. Both the 2" and 1.25" accessory collars feature a
secure twist-tight locking mechanism.
Focuser tension
thumbscrew
1.25" adapter
2" Accessory collar

5
new telescope outside under a starry sky. Be sure to allow the
telescope to equilibrate to the outdoor temperature for at least
30 minutes before using it; this ensures the best, most stable
image quality.
Connecting the EON ED90T CF to a Telescope
Mount
The EON ED90T CF refractor comes with a pair of sturdy, hinged
tube rings on the bottom of which a Vixen-style dovetail mounting
bar is attached. On top of the rings a convenient carrying handle
is pre-installed. The handle can be removed should you desire
to instead install an optional dovetail plate on the tube rings for
attachment of a second telescope or a guide scope, for instance.
You will need a 5mm Allen wrench (not included) to remove the
socket head cap screws attaching the handle to the rings.
On the top and bottom surfaces of the rings are multiple M6-1.0
tapped holes for attachment of dovetail plates.The handle, which
is Arca-Swiss compatible, has three holes on top: the middle is
¼"-20 and it is anked by two M6-1.0 holes.
Balancing the telescope can be done by moving the telescope
within the tube rings to the extent possible, or by sliding the
dovetail mounting plate forward or back in your mount’s saddle.
Observing with the EON ED90T CF
To observe with the EON ED90T CF you will need either a 1.25"
or 2" diagonal and an eyepiece, each sold separately. Because
the optics are made with high-quality ED glass, the eyepieces
you choose should also have excellent, fully multi-coated optics
to utilize the full performance of the telescope. It is desirable to
have a range of eyepieces of different focal lengths, to allow view-
ing over a range of magnications.
To calculate the magnication, or power, of a telescope, simply
divide the focal length of the telescope by the focal length of the
eyepiece.The focal length of the ED90T CF is 540mm.
So an optional 20mm eyepiece would yield a magnication of
540/20 = 27x.
If outside viewing conditions are ideal, a telescope with good
optics can achieve a magnication of about 60x per inch, or 2.4x
per millimeter, of aperture. Keep in mind that at higher powers,
an image will always be dimmer and less sharp (this is a funda-
mental law of optics). In most cases the steadiness of the air (the
“seeing”) will limit how much magnication the scope can toler-
ate, rather than the telescope itself.
Always start viewing with your lowest-power (longest focal
length) eyepiece in the telescope. After you have located and
observed the object with it, you can try switching to a higher-
power eyepiece to ferret out more detail, if atmospheric condi-
tions permit. If the image you see is not crisp and steady, reduce
the magnication 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,
over-magnied image.
Imaging with the EON ED90T CF
Given its high-quality apochromatic optics and fast f/6.0 focal
ratio, the EON ED90T CF excels for astrophotography with
a dedicated astronomical CCD/CMOS camera or a DSLR or
mirrorless camera.As mentioned previously
For optically fast refractors such as the EON ED90T CF, an
optional eld attener is a desirable accessory to compensate
for inherent eld curvature. The attener will ensure tight, sharp
stars out to the edge of your imaging sensor, and is highly recom-
mended if you are using a camera with an APS-C size sensor or
larger. The Orion Field Flattener for Short Refractors (#8893) is
a perfect match for this instrument.
Alternatively, our 0.8x Focal Reducer (#8894), which also at-
tens the image, can be used if you desire a wider imaging area.
This focal reducer shortens the effective focal length of the EON
ED90T CF from 540mm to 432mm, which changes the focal ratio
from 6.0 to an even faster 4.8.
The Field Flattener and Focal Reducer adapters both have a
backfocus distance of 55mm, measured from the rear surface
of the adapter. Backfocus distance is the distance to reach
the image plane, or focus point. You need to insure that your
camera’s sensor sits 55mm back from the rear surface of the
adapter. For DSLRs and mirrorless cameras used with a stan-
dard 42mm or 48mm T-ring, the sensor distance will typically
be 55mm. For astronomical cameras, the sensor usually sits
closer to the front of the camera, so some additional spacing
will be necessary between the eld attener or focal reducer and
the camera to achieve the necessary 55mm backfocus. Orion
offers 42mm T-ring extension rings (#5528) and 48mm extension
rings (#52715) to help achieve focus with any number of different
cameras.You’ll want to get within about +/-2mm of the specied
backfocus requirement to ensure a sharp image.
The 2.5" dual-speed rack-and-pinion focuser of the EON ED90T
CF is capable of handling the weight of your CCD or DSLR
camera and accessories, up to 19 lbs. The drawtube tension is
set at the factory and should not need adjusting. After installing
your camera equipment onto the focuser, check the focuser for
any slippage. If it slips under the weight of the camera, you may
need to add more tension to the focuser. Do this by lightly tight-
ening the focuser tension thumbscrew (Figure 4).
Note About Chromatic Aberration
Chromatic aberration literally means color distortion. Whenever
light passes through one material to another,
different wavelengths (color) are bent by different amounts.This
is a problem that plagues refractor-type telescopes, since light
passes through both air and glass to form an image. Most astro-
nomical objects emit a spectrum comprised of many different
wavelengths of light, so each wavelength will be bent by a slightly
different amount when passing through a lens. This results in
each color of light reaching precise focus at a slightly different
point, which will provide a soft image with a halo of unfocused
color.
The EON ED90T CF is designed to minimize chromatic aber-
ration. The objective lens assembly comprises three individ-
ual lenses, one of which is made from high-performance Hoya
FCD100 ED glass. The use of this ED glass minimizes the
Magnication = Telescope Focal Length (mm)
Eyepiece Focal Length (mm)