ORION TELESCOPES & BINOCULARS 51874 User manual

#51875
#51874
Orion®10" and 12" f/8 Truss
Tube Ritchey-Chrétien
Astrographs
#51874 10" TTRC, #51875 12" TTRC
IN 632 01/19
INSTRUCTION MANUAL
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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 Truss Tube Ritchey-Chretien Astrograph (TTRC). These compact but large-aperture
telescopes are designed and optimized for high-performance astrophotography with CCD and DSLR cameras. Sporting an optical
design comprising hyperbolic primary and secondary mirrors, the RC is highly regarded by advanced astrophotographers and pro-
fessional observatories worldwide. Even the vaunted Hubble Space Telescope is a Ritchey-Chrétien. Orion TTRCs deliver excep-
tional image quality and resolution with zero image shift and minimal coma. Either one of these superb instruments, when paired
with a solid mount, will take your imaging pursuits to a whole new and very exciting level.
Unpacking Your Telescope
Use care when unpacking the shipping carton. We recommend
keeping the box and all original packaging materials. In the
event that the telescope needs to be shipped to another loca-
tion, or returned for warranty repair, having the proper packag-
ing 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. Make sure that all the items listed in
the Parts List below are present.
Parts List
QTY ITEM
1 Truss Tube RC optical tube assembly
1 2" Extension ring
2 1" Extension rings
1 Secondary mirror dust cover
1 Primary mirror dust cover
1 Battery holder (for fans)
Truss Tube Design
Orion TTRC telescopes feature a Serrurier truss design -- the
same truss conguration as the 200-inch Hale telescope at the
Palomar Observatory! Developed by engineer Mark U. Serrurier
in 1935 specically for the Hale telescope, this design utilizes
two sets of opposing truss tubes on either side of the declina-
tion pivot plane. The trusses are designed to effect an equal
amount of exure, which allows the optics to stay on a common
optical axis. When exing, the "upper" truss resists tension and
the "lower" truss resists compression. This keeps the optical
elements parallel to each other no matter how the telescope is
oriented, thus keeping optical collimation precisely intact.
The truss tubes in the Orion TTRC telescopes are made of a
carbon ber-reinforced composite material with a very low ther-
mal expansion prole. Stainless steel ball and socket hardware
connects the truss tubes to the telescope’s three large CNC-
machined aluminum support plates.
The truss design of the optical tube is of course an open tube
design. While both the primary and secondary mirrors are
recessed within baffled cylindrical housings, it is still possible
that ambient light from one’s observing or imaging location
could have an adverse effect on image contrast. It’s best to use
these telescopes at a truly dark site to avoid such intrusions. If
necessary, however, you should consider making or purchasing
an opaque fabric “shroud” to cover the tube assembly between
the front and rear plates. A shroud will block stray light from
entering the optical path as well as help to prevent dew forma-
tion on the mirrors.
The 3.3"Linear Bearing
Crayford Focuser
Orion TTRC telescopes come standard with a CNC-machined,
3.3” dual-speed (10:1) linear bearing Crayford focuser (Figure
1). The linear bearing feature consists of a stabilizing track on
the underside of the drawtube that provides extra rigidity for
carrying heavy payloads (Figure 2). Drawtube exure is vir-
tually eliminated by stabilizing the drawtube within the focuser
housing. The oversized 3.3"-diameter drawtube terminates in a
2" compression ring accessory collar, and a 1.25" compression
ring accessory collar is also included.
The focuser’s 10:1 ne focus adjustment helps you zero in on
the exact focus point. Every 10 turns of the small, black ne
focus knob equals a single turn of the large coarse focus knob,
to enable the micro-adjustment necessary for the sharpest
images possible. Use the coarse focus knob until your object is
as close to focus as possible, then make ne adjustments with
the black ne focus knob.
The focuser is also equipped with both a tension adjustment
knob for the drawtube and a drawtube locking knob.
The tension adjustment knob is on the underside of the focuser
while the locking knob is on top. We recommend keeping the
tension adjustment knob fairly tight at all times as this will mini-
mize drawtube exure and slippage.
The focuser can be rotated to a desired angle prior to nal
focusing for astrophotographic framing by slightly loosening the
focuser attachment collar (turning it counterclockwise), then
rotating the focuser to the desired position before retightening
the collar.
Extension Rings
Included with your Orion TTRC telescope are three thread-on
extension 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
WARNING: Never look directly at the Sun through
your telescope—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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designed for installation individually or in combination between
the optical tube and the focuser to take up unneeded backfo-
cus. Refer to the Specifications at the end of this manual for the
native backfocus distance of the Truss Tube Ritchey-Chretien
telescopes.
If the focuser drawtube is fully extended and you are still unable
to achieve focus you will need to install one or more
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. To do so you must rst remove the focuser from the
optical tube by rotating the focuser attachment collar counter-
clockwise. Then thread the desired extension ring(s) onto the
male threads on the telescope tube (Figure 4). Finally, re-
attach the focuser by aligning the silver attachment collar over
the exposed extension ring threads and turn it clockwise until
tight. It may be useful to experiment with different combinations
during the day before heading out into the eld. Choose a target
over ½ mile away to ensure you are simulating innity focus.
The goal is to reach focus with as little extension of the focuser
drawtube as possible, to avoid drawtube exure.
Depending on what equipment you use to observe or image
with, you may need to add one or more of the included exten-
Figure 3. The TTRC
includes one 2” and two
1” thread-on extension
rings as well as a
battery holder (eight AA
batteries not included).
Figure 1. The 3.3"dual-speed linear bearing Crayford focuser
features both 2"and 1.25"compression ring accessory collars.
Drawtube
lock knob Focuser
attachment
collar
Fine
focus
knob
Coarse focus
knobs
2" accessory
collar
1.25" accessory collar
Figure 2. The focuser’s stainless steel linear bearing rail adds extra
rigidity to support heavy camera loads.
Tension
adjustment
knob
Linear
bearing
Figure 4. Remove the focuser to thread one or more extension rings
onto the focuser tilt adjustment plate, then attach the focuser to the
extension ring.
Focuser tilt
adjustment
plate
2"
extension
ring
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sion rings. The backfocus distance of your camera’s sensor as
well as the other components in your imaging train, e.g., focal
reducer or attener, lter wheel, or off-axis guider, will inuence
how much extension you will need to add between the optical
tube and the focuser in order to reach focus.
Upper and Lower Mounting
Bars
Orion Truss Tube Ritchey-Chretien astrographs have a D-style
(Losmandy) dovetail mounting bar on both the top and bottom
sides of the optical tube assembly (Figure 5). The bottom bar
is for mounting the telescope on a compatible telescope mount
equipped with a saddle that can accommodate a D-plate. The
top bar allows piggyback mounting of a second telescope, a gui-
descope (or, as noted below, a nder scope with an optional
dovetail nder scope base) or other accessories. Attachment to
the dovetail bar will require adapter(s) compatible with a D-style
bar. The length of the dovetail bars on the 10" TTRC are 9.8",
while those on the 12" TTRC are 14".
Attaching Optional Finder
Scopes and Guiding
Solutions
Orion TTRC telescopes are equipped with a dovetail nder
scope base (Figure 5), which allows attachment of any Orion
nder scope or reex sight. It should also be noted that the top
D-type mounting bar on the telescope has two sets of predrilled
and tapped holes that allow attachment of an Orion dovetail
nder scope base (part #7214) to the bar, should you desire to
mount one there. The screws that are included with the #7214
dovetail base t the pre-tapped holes in the bar.
Cooling the Telescope
Before observing or photographing with your Orion TTRC tele-
scope, you should let it equilibrate to the outdoor temperature
for a half hour or so. This will reduce thermal air currents that
could soften or blur your images. Orion TTRC telescopes are
each equipped with three small, low-vibration DC cooling fans
on the rear cell to help accelerate the primary mirror cool-down
time (Figure 6). The fans pull air in through the rear cell and
blow it onto the back of the primary mirror, to facilitate thermal
equilibration. The fans require a 12V power supply; a battery
holder is included that accepts eight AA batteries (not included).
A cable from the battery holder plugs into the DC input port on
the rear cell. The fans start up as soon as the battery pack is
plugged in; there is no ON/OFF switch. Alternatively, the fans
can be powered by a rechargeable 12V DC eld battery that has
a 5mm/2.1mm plug.
Although the fans are a low-vibration model, we recommend
turning them off while actively imaging to avoid any effect on
image stability from vibration or blowing air.
Figure 6. The rear cell of the TTRC has three built-in 12V
DC-powered fans and collimation adjustment screws for both the
primary mirror and focuser.
Primary mirror
collimation
screws
Cooling fan (x3)
DC power input portFocuser tilt adjustment screws
Figure 5. D-style dovetail bars are installed on both the top and
bottom of the telescope (top bar shown). Two sets of threaded holes
on the bar accommodate an optional Orion dovetail finder scope
base.
Two pairs of holes for
optional nder scope base
Finder
scope
base
Top
dovetail
bar
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Collimation
The optics in your new TTRC have been aligned at the factory.
However, rough handling during transit may warrant periodic re-
adjustments. The secondary mirror is precisely center marked
with a small adhesive ring (Figure 7) to aid in collimation. This
ring does not affect the view through the telescope, so it should
not be removed. You will need a laser collimator or a Cheshire
eyepiece to check and adjust collimation. We recommend doing
the collimation during the daytime; it can be done indoors.
Remove any extension rings and attach the focuser directly to
the optical tube. Set up your telescope in a well-lit room with
the telescope oriented horizontally, and point it at a light colored
wall.
Focuser Tilt Adjustment
The first step will be to check that the focuser is precisely
aligned with the secondary mirror. On the TTRCs, the focuser is
independently collimatable. This step is best done with a laser
pointer.
Insert the laser pointer into the 1.25" or 2" focuser collar (depend-
ing the on the diameter of your laser collimator’s barrel) and turn
it on. Assuming the laser collimator beam is exactly parallel with
the collimator’s mechanical axis, the laser beam should hit the
secondary mirror exactly in the middle of the center ring on the
secondary mirror. If it does, you can skip to the next section,
“Secondary Mirror Adjustment.”
If the laser dot does not land in the middle of the center ring on
the secondary mirror, you need to adjust the tilt of the focuser
as follows.
You will use the three sets of three screws on the focuser tilt
adjustment plate, shown in Figure 6. Each set consists of a
center silver-colored socket head screw anked by two smaller
black socket head screws. The small black screws are mere-
ly locking screws, which you should loosen a couple of turns
before adjusting the mirror’s tilt. The larger silver screws are
spring-loaded collimation screws that tilt the focuser. You will
need a 2mm and 4mm Allen wrench to adjust the small and
large screws, respectively.
Turn the collimation screws only a fraction of a turn at a time.
Turn one clockwise or counterclockwise and then check wheth-
er the laser dot is centered in the secondary mirror ring, or is
closer to center, or farther from center. Using trial and error,
keep tweaking the collimation screws accordingly, each time
checking the laser dot’s position in the center ring.
When the laser dot is nally exactly centered in the ring, lightly
tighten all six locking screws to x the focuser in that tilt position.
Secondary Mirror Adjustment
The next step will be to adjust the tilt of the secondary mirror.
This can also be done with a laser collimator, however we will
describe doing it with a simple Cheshire collimating eyepiece.
NOTE: Only adjust the three screws around the perimeter
of the secondary mirror holder -- do not adjust the center
screw! (Figure 8). Adjusting the center screw can change
the distance between the primary and secondary mirrors,
which you do not want to do, or could even cause the sec-
ondary mirror to fall off, which will not be covered under
warranty.
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 ashlight,
is aimed at the 45° reecting surface of the Cheshire.
Figure 7. A small adhesive ring marks the exact center of the
secondary mirror, to aid in precise collimation.
Secondary
mirror
Center ring
Figure 8. Secondary mirror collimation is done by adjusting the
three socket head capscrews on the front of the telescope.
Collimation
adjustment
screws
Do not
adjust
center
screw!
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