Orion Ritchey-Chretien 8268 User manual

INSTRUCTION MANUAL
IN 361 Rev. B 5/15
Customer Support (800)676-1
Corporate Offices [phone] • 89 Hangar Way, Watsonville, CA 95076
®

#8268 6" f/9 RC
#8267 8" f/8 RC
#8266 10" f/8 RC
Providing Exceptional Consumer Optical Products Since 1975
OrionTelescopes.com
#8268
#8266 #8267

2
Congratulations on your purchase of an Orion
Ritchey-Chretien astrograph. These compact but
large-aperture telescopes are designed and opti-
mized for high-performance astrophotography
with CCD and DSLR cameras. Sporting an optical
design comprising hyperbolic primary and second-
ary mirrors, the RC is highly regarded by advanced
astrophotographers and professional observato-
ries worldwide. Even the vaunted Hubble Space
Telescope is an RC! Orion RCs deliver exceptional
image quality and resolution with zero image shift,
minimal coma, a highly baffled steel tube for out-
standing contrast, and exclusive mounting options
for optional finder scopes and guide scopes. Any
one of these superb instruments, when paired with
a good mount, will take your imaging pursuits to a
whole new and very exciting level.

1 Optical tube assembly
1 2" Extension ring
2 1" Extension rings
1 Battery holder (10" RC only)
1 Starry Night SE digital download coupon
 Never look directly at the Sun with
the naked eye or with a telescope – unless you
have a proper solar filter installed over the front of
the telescope! Otherwise, permanent, irreversible
eye damage may result.

Use care when unpacking the shipping carton. We recom-
mend keeping the boxes and all original packaging materi-
als. In the event that the telescope needs to be shipped to
another location, or returned for warranty repair, having the
proper packaging will ensure that your telescope will survive
the journey intact. Returns for refund or exchange will not be
accepted without all of the original packaging. Once all items
have been removed from the box take a moment to confirm
that all pieces are present and intact. Refer to the Parts List to
aid in identifying the included items.

All Orion Ritchey-Chretien telescopes come standard with
a machined, all-aluminum, dual-speed focuser. The 6" RC
features a 2" Crayford focuser equipped with a removable
1.25" adapter (Figure 1A). The 8" RC has a 2" linear-bearing
Crayford focuser, which has a stabilizing track on the under-
side of the drawtube that provides extra rigidity for carrying
heavy payloads (Figure 2). Drawtube flexure is virtually elimi-
nated by stabilizing the drawtube within the focuser housing.
The 10" RC also boasts a linear bearing focuser, but with an
oversized housing and a larger 3.3" drawtube that terminates
in a 2" accessory collar.
The focuser on all three RCs has a 10:1 fine focus adjust-
ment. Every 10 turns of the small knob equals a single turn of
the large knob, to enable the micro-adjustment necessary for
the sharpest images possible. Use the coarse focus knob to
adjust the telescope until your object is as close to focus as
possible, then make fine adjustments with the black outside
knob.
Each focuser is also equipped with both a tension adjustment
knob for the drawtube and a drawtube locking knob. On the 6"
RC both knobs are on the underside of the focuser (Figure
1B), whereas on the 8" and 10" models the tension adjust-
ment knob is on the underside of the focuser while the larger
locking knob is on top (Figure 2). We recommend keeping
the tension adjustment knob fairly tight at all times as this will
minimize drawtube flexure and slippage.
The focuser can be rotated to a desired angle prior to final
focusing for astrophotographic framing by slightly loosening
the focuser attachment collar (turning it counterclockwise),
then rotating the focuser to the desired position, then retight-
ening the collar.

3
Grip-ring
Coarse focus knob
Brass compression ring
1.25" adapter
Drawtube
Thumbscrew locks2" accessary collar
Coarse focus knob
Millimeter and inch scales
Fine focus knob
Focuser attachment collar
Dovetail finder
scope bases
A) The 6" RC’s Crayford focuser, top view. B) Both the drawtube tensioning and lock knobs are located on the
underside of the focuser.
A
Drawtube
lock knob
Drawtube tension
adjustment knob
B

4

Included with your RC telescope are three thread-on exten-
sion rings (Figure 3). These extension rings are provided to
allow multiple visual or photographic accessories to reach
focus, depending on their backfocus requirements. They
are designed for installation individually or in combination
between the optical tube and the focuser to take up unneeded
backfocus. Refer to the Specifications at the end of this man-
ual for the native backfocus distance of each Ritchey-Chretien
model.
If the focuser drawtube is fully extended and you are still
unable to achieve focus you will need to install one or more-
extension rings. To do so you must first remove the focuser
from the optical tube by rotating the focuser attachment collar
counterclockwise (refer to Figure 2). Once you have thread-
ed on the desired number of extension rings onto the male
threads on the telescope tube, re-attach the focuser by align-
ing the silver attachment collar over the exposed extension ring
threads and tighten by carefully turning clockwise (Figure 4). It
may be useful to experiment with different combinations dur-
ing the day before heading out into the field. Choose a target
over ½ mile away to ensure you are simulating infinity focus.
The goal is to reach focus with as little extension of the fo-
cuser drawtube as possible, to avoid drawtube flexure.
Depending on what equipment you use to observe or image
with, you may need to add one or more of the included exten-
sion rings. The examples listed and pictured in Figure 5 are
Coarse focus knob Fine focus knob
Focus attachment collar
1" extension ring
2" extension ring
1.25" adapter
Drawtube lock knob
Drawtube
Drawtube tension
adjustment knob
Thumbscrew locks
2" accessary collar
Linear bearing
The linear bearing Crayford focuser on the 8" and 10"
RCs provide extra drawtube rigidity to support heavy camera loads.
(8" RC shown)
Extension rings are installed between the telescope’s
rear cell and the focuser, to take up unneeded backfocus.
Each RC comes with one 2" and two 1"
extension rings.
of common scenarios. So for instance, for DSLR cameras and
most visual applications you will need 3" of extension (one 1"
ring and one 2" ring) between the OTA and the focuser. Larger
2" eyepieces may require only 2" of extension. Some setups
may require combinations different from those shown. The
backfocus distance of your camera’s sensor as well as the
other components in your imaging train, e.g., focal reducer
or flattener, filter wheel, or off-axis guider, will influence how
much extension you will need to add between the OTA and
the focuser in order to reach focus.

5
T-ring 2" camera
adapter
2" camera
adapter
CCD Camera Focuser
2" extensionFocuser 1" extension
2" extension 1" extension
Focuser
(w/ 1.25" adapter)
Diagonal
Eyepiece
2" extension 1" extension
1" extension
Optical tube
Optical tube
Optical tube
DSLR
camera body
DSLR Camera
Configuration
Typical CCD Camera
Configuration
Standard Visual
Configuration
Off-axis guiderCCD Camera Focuser 2" extension
Optical tube
CCD with
Off-Axis Guider
Configuration
Connection diagrams for typical RC uses.

6


Unlike other Ritchey-Chretien telescopes on the market,
Orion RCs feature two dovetail finder scope bases on oppo-
site sides of the telescopes’ vertical mid-line (refer to Figure
1A), to allow maximum versatility of placement for optional
finder scopes, reflex sights, or a mini guidescope. Having two
dovetail bases gives you the option of placing a finder scope
on either the left or right side of the focuser, depending on
your preference, or of mounting both a red-dot sight and a
traditional achromatic finder scope on the telescope simulta-
neously. For imaging, you may even wish to install a small
Two included finder scope dovetail bases allow
installation of an optional mini 50mm guidescope and autoguide
camera on one side of the focuser and an optional finder scope on
the other. (6" RC shown)
Slotted plates on the top side of the 8" and 10" RCs
allow mounting of a guide scope for astrophotography or of another,
auxiliary telescope.
The 10" RC is equipped with three integrated 12V DC
cooling fans, which are powered by user-supplied AA batteries
guidescope such as the Orion 50mm Mini GuideScope in one
of the dovetail bases along with a reflex sight or another finder
scope for visual use in the other, as shown in Figure 6. The
choice is yours!
The 8" and 10" RCs also feature slotted universal dove-
tail bars on top of the tube (Figure 7), custom designed by
Orion, to allow mounting of a guidescope or a DSLR camera
for piggyback photography, or even a second, piggybacked
telescope for visual use or imaging. The top bar on the 8" RC
is a Vixen-style bar while the bar on top of the 10" is a wider,
Losmandy-style bar. With two long slots and multiple through-
holes, these solid aluminum bars can be used to mount guide
scope rings or tube rings spaced apart by the distance you
need for your guide scope or second telescope. No other RCs
on the market are equipped with these versatile top-side uni-
versal mounting bars.

Orion Ritchey-Chretien astrographs each have a dovetail
mounting bar running the full length of the optical tube for
rigid attachment to a compatible equatorial mount saddle
plate. The 6" RC has a narrow, Vixen-style bar while the 8"
and 10" include a wide, Losmandy-style bar. The long length
of the dovetail bars makes it easy to balance the RC on the
declination axis by sliding the scope forward or back before
locking it down.

Before observing or photographing with your RC, you should
let it equilibrate to the outdoor temperature for an hour or more.
This will reduce thermal air currents inside the telescope that
could soften or blur your images, whether you’re doing visual
observing or astrophotography. Due to the size of its optics,
the 10" RC is equipped with three small DC cooling fans on
its rear cell to help accelerate the cool-down time (Figure 8).
The fans pull outside air in through the rear cell and blow it
Power jack
Fans

7
onto the back of the primary mirror and out the front of the
telescope. It’s best to point the telescope upward when the
fans are on to allow the heat to more efficiently escape.
The fans require a 12V power supply; a battery holder is
included with the 10" RC that accepts eight user-supplied AA
batteries. The cable from the battery holder plugs into the DC
power jack on the rear cell (Figure 8). The fans start up as
soon as the power pack is plugged in; there is no ON/OFF
switch. Alternatively, the fans can be powered by a 12V DC
field battery that has a 5mm/2.1mm plug.
Although the fans are a low-vibration model, we recommend
turning them off while actively observing or imaging to avoid
any effect on the view from vibration or blowing air.


The optics in your new Ritchey-Chrétien optical tube have
been aligned at the factory. However, rough handling during
transit may warrant periodic re-adjustments.We have precise-
ly center marked the secondary mirror with a small adhesive
ring to aid in collimation. This ring does not affect the view
through the telescope, so it should not be removed. You will
need a Cheshire eyepiece to check and adjust collimation.
We recommend doing the collimation during daytime; it can
be done indoors.
1. Remove any extension rings and attach the focuser directly
to the optical tube.
2. Set up your telescope in a well-lit room with the telescope
oriented horizontally, and point it at a light colored wall.
3. Insert the Cheshire eyepiece into the focuser via the
included 1.25" adapter and tighten the thumbscrew on the
adapter. Make sure that a bright source of light, like a ceiling
light or flashlight, is aimed at the 45° reflecting surface of the
Cheshire.
4. Look through the Cheshire eyepiece. You should see a
small black dot and a dark ring within a larger bright circle.
The dot is the hole of your Cheshire eyepiece. The dark ring
is the center mark on the secondary mirror. And the bright
circle is the reflective 45-degree surface of the Cheshire. The
larger black circle outside that is the secondary mirror holder
(Figure 9A).
If your scope is in good collimation, the black dot will be dead
center in the dark ring, which will in turn be centered in the
bright circle. If that’s the case, no further adjustments to the
secondary mirror will be necessary. The optical axis is denot-
ed by a thin white circle on the outer edge. You can disregard
that for the time being; it will be covered in the following sec-
tion.
If the view looks something like Figure 9B — with the dot
of the collimation eyepiece NOT centered in the secondary
center ring — you will need to adjust the three collimation set-
The view through a collimating eyepiece (not to scale). A) Shows the Ritchey-Chrétien aligned with all components identified. B)
Shows the secondary out of alignment. C) Shows the optical axis out of alignment.
Collimation
eyepiece
mark
Secondary mirror
center ring
Secondary
mirror holder
Reflective surface of
collimating eyepiece
Spider
vanes
Optical
axis
A C
B

8
screws at the front of the secondary mirror holder (Figure 10).
This will adjust the tilt of the secondary, changing the relative
position of the secondary center ring when peering through
the collimation eyepiece.

NOTE: Only adjust the three screws around the perimeter
of the holder—do not adjust the center screw! (Figure
10). Adjusting the center screw can cause the secondary
mirror to fall off and will not be covered under warranty.
A 4mm hex key is required to perform collimation on the
secondary mirror. When adjusting one of these screws you
will need to make counter-adjustments to the other two.
Therefore, if you are loosening one screw you will need to
tighten the other two. At the end of the process you want all
three collimation screws to be reasonably tight so the second-
ary mirror won’t shift while the scope is in use.
Always start by loosening one screw. Adjust the screws
only very slightly—by no more than 1/10 turn at a time, and
one screw at a time before checking the view through the
Cheshire again to see how things changed. Only tiny adjust-
ments should be required to achieve collimation. This will
also aid in the prevention of accidently putting the telescope
grossly out of collimation. With each tiny tweak of a screw,
make a mental note of which way and how far the center dot
moved, as that will inform which screw to turn next and by
how much. Experiment with different combinations of loosen-
ing/tightening the three screws one by one until the collima-
tion eyepiece’s black dot is centered in the dark ring of the
secondary mirror.The correct alignment of the secondary mir-
ror is critical in determining if the optical axis requires align-
ment. Be sure you have properly aligned the secondary mirror
before proceeding to the next step.

The optical axis is denoted by a thin outline of light (white)
around the perimeter of the view through the collimating eye-
piece (Figure 9A). If this outline is not a perfect circle of uni-
form thickness, as in 9C, that’s an indication that the optical
: Three pairs of collimation screws on the rear cell
allow adjustment of the optical axis, if needed. (8" RC shown)
Chrome
Collimation
screw
Black lock
screw
The secondary mirror collimation adjustment screws. A
4mm hex key is required.
A de-focused view of a bright star through an
eyepiece. Proper collimation will show concentric, symmetrical
diffraction rings with a dark spot exactly in the center, as in the
image on the right. If the spot is off-center, the scope needs
collimation.
Out of collimation Collimated
Secondary
mirror
collimation
adjustment
screws
Do not
adjust center
screw!
axis (primary mirror) needs adjustment. This adjustment will
require 3mm and 2.5mm hex keys for the 6" and 8" RCs, and
4mm and 2.5mm hex keys for the 10" RC.
Note that there are three pairs of screws on the rear cell of the
optical tube where the focuser attaches (Figure 11). Each pair
consists of a small black screw and a larger chrome screw.
The small black screws are merely locking screws, which
you should loosen before adjusting the mirror’s tilt. The larg-
er chrome screws are spring-loaded collimation screws that
actually adjust the tilt of the primary mirror. Turn these collima-
tion screws only a fraction of a turn at a time. Turn one and
check the view through the Cheshire to see if it improved the
white optical axis ring. Keep tweaking the collimation screws,
each time checking the optical axis ring, until it is concentric
and uniform in width. Then tighten the three lock setscrews to
fix the mirror in that position.
After adjusting the optical axis, re-check the collimation of the
secondary mirror and make any necessary adjustments, then
recheck the optical axis collimation. Optical axis collimation
will not need to be performed very often, if ever.



A star test can be performed to confirm the collimation accu-
racy of the telescope. The adjustment procedure on the tele-
scope is the same as described above; testing, however, will
be done in the night sky using a real star and you will not use
the Cheshire eyepiece.
Choose a star close to the zenith (straight overhead) rath-
er than at the horizon to minimize atmospheric distortions.
Using Polaris as your target star can be helpful as minimal
drift adjustments will be required.
Do not use a star diagonal while performing this procedure.
Rather, place an eyepiece directly into the 1.25" adapter in
the focuser. It should be an eyepiece that provides moder-
ate to high magnification. You may need to add all three of
the extension rings in front of the focuser to be able to reach
focus. Center the star in the field of view. Slowly de-focus the
image with the focusing knob until you can see a series of
concentric diffraction rings form around the dark disk in the
center. That dark disk is the shadow of the secondary mir-
ror. In a well collimated telescope, the diffraction rings should
appear round and concentric, with the dark disk exactly in
the center (Figure 12). If the dark central disk is off center,
the scope is out of collimation. Adjust the collimation of the
secondary mirror and, only if necessary, the primary mirror
while monitoring the defocused star until the dark central disk
is exactly centered in the diffraction rings.
NOTE: It is important when checking or adjusting the col-
limation using a star, that the star be positioned in the
center of the eyepiece’s field of view. If it isn’t, the optics
will always appear out of collimation, even though they
may be perfectly aligned! It is critical to keep the star
centered, so over time you may need to make slight cor-
rections to the telescope’s position.


Do not disassemble the Ritchey-Chrétien for any reason,
including to clean the mirror. A small amount of dust and par-
ticulates on the mirror’s surface will not affect performance. In
the event internal cleaning is necessary the telescope should
be shipped to Orion Telescopes and Binoculars for service.
This telescope does not contain user-serviceable parts and
disassembly of the components will void the warranty. When
not in use, please use the supplied dust cap(s) to keep dust
and particulates out of the tube and off the optics.

10

6" 
Aperture: 6" (150mm)
Focal Length 1370 mm
Focal Ratio f/9
Mirror figure: Hyperbolic
Mirror material BK-7
Mirror Coating Enhanced, 94%-96% reflectivity with SiO2 overcoat
Optical Tube Steel
Focuser 2" Crayford, dual speed (10:1)
Drawtube travel: 34mm
Backfocus distance: 240.1mm from rear cell; 151.3mm from 2” collar on drawtube
Central obstruction: 72mm
Tube Length: 486mm
Tube Diameter: 191mm
Bottom mounting bar: V-style (narrow)
Top mounting bar: None
Cooling fans: None
Weight: 12.1 lbs.

Aperture: 8" (200mm)
Focal length: 1600mm
Focal ratio: f/8
Mirror figure: Hyperbolic
Mirror material: Fused quartz
Mirror Coating: Enhanced, 94%-96% reflectivity with SiO2 overcoat
Optical Tube: Steel
Focuser: 2" Linear-bearing Crayford, dual speed (10:1)
Drawtube travel: 50mm
Backfocus distance: 238.1mm from rear cell; 140.7mm from 2" collar on drawtube
Central obstruction: 95mm
Tube Length: 559mm
Tube Diameter: 232mm
Bottom mounting bar: L-style (wide)
Top mounting bar: V-style (narrow), slotted
Cooling fans: None
Weight: 18.5 lbs.

11

Aperture: 10" (250mm)
Focal length: 2000mm
Focal ratio: f/8
Mirror figure: Hyperbolic
Mirror material: Fused quartz
Mirror Coating: Enhanced, 94%-96% reflectivity with SiO2 overcoat
Optical Tube: Steel
Focuser: 3.3" Linear-bearing Crayford, dual speed (10:1)
Drawtube travel: 50mm
Backfocus distance: 243.9mm from rear cell; 139.6mm from 2" collar on drawtube
Central obstruction: 110mm
Tube Length: 721mm
Tube Diameter: 299mm
Bottom mounting bar: L-style (wide)
Top mounting bar: L-style, slotted
Cooling fans: 3 built-in fans, powered by 12V DC
Weight: 35.3 lbs.

12
Orion Telescopes & Binoculars
Corporate Offices: 89 Hangar Way, Watsonville CA 95076 - USA
Customer Support: www.OrionTelescopes.com/contactus
Copyright © 2015 Orion Telescopes & Binoculars
All Rights Reserved. No part of this product instruction or any of its contents may be repro-
duced, copied, modified or adapted, without the prior written consent of
Orion Telescopes & Binoculars.

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 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 postage paid. Proof of purchase (such as
a copy of the original receipt) is required. This warranty is only valid in the country of purchase.
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. It is not
intended to remove or restrict your other legal rights under applicable local consumer law; your state or
national statutory consumer rights governing the sale of consumer goods remain fully applicable.
For further warranty information, please visit www.OrionTelescopes.com/warranty.