ORION TELESCOPES & BINOCULARS 8961 User manual

INSTRUCTION MANUAL
IN 380 Rev. A 04/10
Customer Support [phone] • E-mail: suppor[email protected]
Corporate Offices [phone] • 89 Hangar Way, Watsonville, CA 95076
Orion®10"
Ritchey-Chrétien
Optical Tube Assembly
#8961
Providing Exceptional Consumer Optical Products Since 1975
OrionTelescopes.com

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Congratulations on your purchase of an Orion
Ritchey-Chrétien astrograph! Astroimaging demands
high contrast and center to edge image sharpness. The
Ritchey-Chrétien optical system features precision hyper-
bolic quartz mirrors with an impressive reflectivity rating of
no less than 94%. These highly corrected optics offer virtu-
ally coma-free performance; and multiple knife-edge baffles
provide images with superb contrast. These design features
will offer a lifetime of outstanding performance for imaging
and visual applications. The Ritchey-Chrétien is a member
of the Cassegrain family of telescopes. This unique design
offers large-diameter optics while maintaining very short tube
lengths, making them extremely portable and versatile.
Parts List
1 Optical Tube Assembly
1 2" Extension ring
2 1" Extension rings
1 Collimation Eyepiece
1 Battery Pack (for cooling fans)
Unpacking Your Telescope
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.
Your new telescope arrives double-boxed (Figures 2a-c).Make
certain you are opening from the top of the box to access the
accessories packaged in the Styrofoam shell. To access the
optical tube simply grasp the Styrofoam piece and lift it out of
the box and set it aside for the time being. 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 above to
aid in identifying the various pieces.
Setting Up Your Telescope
Your Ritchey-Chrétien optical tube comes ready to use right
out of the box. The focuser is attached to the optical tube and
ready to accept either visual or photographic accessories.
Also included are three individual extension rings (Figure 1).
These extension rings are provided to allow multiple visual or
photographic accessories to reach focus. These are designed
to thread directly onto the optical tube. Therefore, the focuser
will need to be removed before attaching the necessary
extension rings. It may be useful to experiment with different
combinations during the day before heading out into the field.
Choose a target over ½ mile away to ensure you are simulat-
ing distant focus.
Figure 1: The Ritchey-Chrétien Optical Tube.
Collimating
eyepiece
Battery
pack Extension rings
Optical tube

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If the focuser drawtube is fully extended and you are still
unable to achieve focus you will need to install one or more
of these extension rings. They are to be installed in-between
the focuser and optical tube. In order to install the necessary
extension ring(s) you will need to first remove the focuser from
the optical tube. Be careful not to cross-thread these pieces
when re-attaching adapters.
Remove the focuser by gently turning the knurled silver1.
grip-ring with the both hands (Figure 3). Turn counter-
clockwise to loosen.
Attach the extension ring of choice to the backend of2.
the tube. The optical tube has external (male) threads.
Subsequently you will use the end of the ring with internal
(female) threads to attach.
The exposed threads on the back of the extension tubes3.
match that on the OTA to install additional extension rings
or to reattach the focuser.
Once you have added the desired number of extension4.
rings re-attach the focuser by aligning the silver grip-ring
over the exposed extension ring threads and tighten by
carefully turning clockwise.
The wide variety of astronomical equipment available will
require that you add or remove some or all of the extension
rings. Individual setups will require different combinations of
extension rings be used. In general, visual applications will
require further extension than imaging. The examples listed
and pictured on the following page (Figures 4a-d) are of com-
mon scenarios. Some setups may require combinations dif-
ferent from those listed below.
To use an Orion StarShoot Deep Space imager use three
inches worth of the supplied extension rings to reach focus.
For DSLR use – and most visual applications – 2" worth of
extension will be required. Larger 2" eyepieces may only
require one inch of extension.
Focusing the Telescope
One of the exciting new features of the Orion Ritchey-Chrétien
optical tubes is the inclusion of the new dual-speed (10:1) 3"
linear bearing Crayford focuser (Figure 5). Instead of the tra-
ditional Crayford-style focuser – which uses a roller tensioned
against the drawtube – the new linear bearing focuser has a
track on the drawtube with beveled edges and rollers within
“grooves” along the edges. This allows you to more effectively
lock down the focuser with heavy payloads such as a large
eyepiece, a DSLR, or a large CCD Imager and further reduc-
Figure 3: Removing the focuser.
Figures 2a-c: Unpacking the Optical Tube.
Grip-ring
2a
2b
2c

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T-ring 2" camera
adapter
2" camera
adapter
StarShoot CCD
Imager
Focuser
2" extensionFocuser
2" extension 1" extension
Focuser
(w/ 1.25" adapter)
Diagonal
Eyepiece
2" extension
1" extension
Optical tube
Optical tube
Optical tube
DSLR
camera body
DSLR Camera
Configuration
StarShoot Deep
Space Imager
Configuration
Standard Visual
Configuration
4a.
4b.
Off-axis guiderStarShoot CCD
Imager
Focuser
Optical tube
StarShoot with
Off-Axis Guider
Configuration
4c.
4d.
Figure 4a-d: Possible accessory configurations using the Ritchey-Chrétien OTA.

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es image shift by stabilizing the drawtube within the focuser
housing.
The 3" drawtube results in a larger image circle and a fully
illuminated field on the imaging sensor of all imagers; includ-
ing DSLR’s and large format CCD imagers. The focuser has
50mm of drawtube travel and a total back focus of 150mm from
the rear of the 2" adapter. This generous amount will allow
comprehensive use of the accessories preferred by serious
astroimagers, including filter wheels, autoguiders, and adap-
tive optics guiding systems such as the Orion SteadyStar.
For astronomical viewing, out-of-focus star images are very
diffuse, making them difficult to see. If you turn the focus knob
too quickly, you can go right through focus without seeing the
image. To avoid this problem, your first astronomical target
should be a bright object (like the Moon or a planet) so that
the image is visible even when out of focus. There is also a
10:1 fine focus adjustment. 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.
Attaching a Finder Scope
A finder scope is a small, wide-field telescope used to help
locate and center objects in the main field of your telescope. A
finder scope usually has a built-in crosshair reticle that shows
the optical center of the finder’s field of view. On some models
the center is indicated with an LED display.
A finder scope dovetail holder has been pre-installed on your
Ritchey-Chrétien optical tube assembly making it easy to
use any Orion finder and many others using a similar bracket
(Figure 6). Installing a finder scope is very simple:
Loosen the metal thumbscrew on the side of the dovetail1.
base.
Insert the bracket into the dovetail from the back of the2.
telescope, until it stops.
When the finder bracket is securely in place retighten the3.
metal thumbscrew.
Cooling Fans
There are three 1.5" DC powered fans built into the rear cell
of the 10" Ritchey-Chrétien telescope (Figure 8). These will
reduce the time it takes to achieve thermal equilibrium of the
primary mirror. Having your optics at the same ambient tem-
perature as your surroundings will eliminate tube currents and
allow you to achieve a sharper focused image. The fans can
be powered by 8 AA batteries (not included) using the sup-
plied battery pack, or and external 12 V field battery such as
the Orion Dynamo Pro. It is suggested to power the cooling
fans 45 minutes to an hour prior to viewing or imaging with
the Ritchey-Chrétien. You may need to allow additional time
for cooling if there is a substantial temperature difference
between the storage and viewing environments. Once the
telescope has achieved thermal equilibrium you can power off
the cooling fans to reduce vibration.
Collimating the Ritchey-Chrétien
Your new Ritchey-Chrétien optical tube has been aligned
at the factory. However, rough handling during transit may
require periodic re-adjustments. We have center-marked the
secondary mirror and included a collimation eyepiece to aid
in this process.
Using the Collimating Eyepiece
This is the recommend procedure for most users. Setup your
telescope in a well lit room pointed horizontally. It is best to
remove the lens cover and point the telescope at a white
(or light colored) wall. Remove all of the extension rings and
attach the focuser directly to the optical tube. Insert the col-
limation eyepiece into the focuser using the 1.25" eyepiece
adapter. When peering through the collimation eyepiece you
should see a small black dot centered within a donut-like ring.
The black dot is the mark of the collimation eyepiece and
the ring is the center target on the secondary mirror. The big
white circle outside that is the reflected surface of the col-
Figure 6: Finder scope dovetail base.
Finder scope
dovetail holder
Metal
thumbscrew
Figure 5: Details of the linear bearing Crayford focuser.
Knurled
silver
grip-ring
Coarse
focus knobs
10:1 Fine
focus knob
Focus
tension knob
Focus
lock knob

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limation eyepiece and the larger black circle outside that is
the secondary holder. The optical axis is denoted by a thin
white circle on the outer edge. You can disregard that for the
time being it will be covered in the following section. If this
is aligned as in Figure 9a, no further adjustments will be
necessary. If it appears as in figure 9b – with the dot of
the collimation eyepiece not centered in the secondary center
mark – use the three collimation screws at the front of the
secondary mirror holder. This will adjust the tilt of the sec-
ondary changing the relative position of the secondary mark
when peering through the collimation eyepiece.
Secondary Adjustment
NOTE: Only adjust the three screws around the perimeter
of the holder. Do not adjust the center screw. Adjusting
the center screw can cause the secondary mirror to fall
off and will not be covered under warranty (Figure 7).
A 4mm hex key is required to perform collimation on the sec-
ondary mirror. When adjusting one of these screws you will
need to make equal counter-adjustments to the other two.
Therefore, if you are tightening one screw you will need to
loosen, by an equal amount, the other two. When the process
is complete you should have tension against all three screws.
Adjust the screws by no more than ¼ turn at a time. Only
minor adjustments should be required to achieve collimation.
This will also aid in the prevention of accidently putting the
telescope grossly out of collimation in the event adjustments
are made incorrectly. Experiment with different combinations
until the collimation eyepiece mark is centered in the center
mark of the secondary mirror. The correct alignment of the
secondary mirror is critical in determining if the optical axis
requires alignment. Be certain you have properly aligned the
secondary mirror before proceeding to the next step.
Primary Mirror Adjustment
These adjustments will require a 3mm and 2.5mm hex key.
There are three sets of “push-pull” screws on the back-end of
the optical tube where the focuser attaches (Figure 8).
Each set consists of a smaller black screw and a larger chrome
screw; these must be adjusted in tandem. Loosen one and
tighten the other to make changes to the optical axis. This will
adjust the tilt of the optical axis in relation to the secondary
mirror. When properly aligned you will see a very thin con-
centric outer white circle around the perimeter of your view
through the collimation eyepiece. This procedure will require
only micro-adjustments, if any.
Star Testing
An optional star test can be performed to confirm the collima-
tion accuracy of the telescope. The adjustment procedure on
the telescope is the same as using the Collimation eyepiece;
testing, however, will be done in the night sky. This method is
more difficult as you will need to keep your target star cen-
tered in your field of view. Furthermore, seeing conditions will
affect the end result. Keeping the star precisely centered in
the field of view is critical to avoid false negatives. It is sug-
gested that you choose a star close to the zenith (straight
overhead) rather than at the horizon to minimize atmospheric
distortions. Using Polaris as your target star can be helpful as
minimal drift adjustments will be required.
Figure 8: The Ritchey-Chrétien 10" OTA primary adjustment
screws and cooling fans.
Figure 7: The secondary mirror collimation adjustment screws.
Secondary
mirror
collimation
adjustment
screws
Do not
adjust center
screw.
Collimation
adjustment
push-pull screws
DC 12V
power jack for
cooling fans
Cooling
fans

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Center a bright star in your field of view using moderate to
high magnification. Place your eyepiece directly into the fo-
cuser. Do not use a star diagonal while performing this proce-
dure. In a well collimated telescope, a defocused star image
should appear symmetrical, with the dark central obstruction
centered in the star’s ring pattern (Figure 10).
Care and Cleaning of the Optics
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-servicable 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 mirror.
Figure 9a-c: The view through the collimating eyepiece (not to scale). Figure 9a shows the Ritchey-Chrétien aligned with all components
identified. Figure 9b shows the secondary out of alignment. Figure 9c shows the optical axis out of alignment.
Figure 10: An unfocused view of a bright star through
the eyepiece. Proper collimation will show a symmetrical
diffraction pattern such as the one on the right. If the circles are
unsymmetrical the scope needs collimation.
Collimation
eyepiece
mark
Secondary mirror
center mark
Secondary
mirror holder
Reflective surface of
collimating eyepiece
Spider
vanes
Optical
axis
Border
9a 9c
9b
Out of collimation Collimated

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Specifications
10" f/8
Optical tube material: Steel
Optical configuration: Ritchey-Chrétien
Figure: Hyperbolic
Mirror material: Quartz
Mirror coating: Enhanced, no less than 94%
with SiO2Overcoat
Focuser: Machined Aluminum 3" Dual-
Speed (10:1) Linear Bearing
Crayford
Focus travel: 50mm
Back focus: 150mm
Cooling fan: 3 total 1.5" diameter 12v DC
Accessories: Accepts 2" & 1.25"
Specifications
Baffles: 9 knife-edge computer
positioned baffles plus
internal micro-baffles along
primary mirror baffle tube
and secondary mirror light
shield
Optical tube: Steel
Aperture: 250mm (9.8")
Focal length: 2000 mm
Focal ratio: f/8
Secondary center marked: Yes
Secondary mirror minor axis: 105mm
Central Obstruction: 111mm; 44% obstruction by
diameter
Length: 29"
Diameter 11.8"
Weight: 34.5 lbs.
One-Year Limited Warranty
The Orion Ritchey-Chrétien 10" Optical Tube Assembly is warranted against defects in materials or work-
manship 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
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: Orion Customer Service [phone]; suppor[email protected].
Orion Telescopes & Binoculars
OrionTelescopes.com
89 Hangar Way, Watsonville CA 95076
Customer Support Help Line [phone]