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Thank you for choosing this
Astro-Tech AT8RC
8” f/8
Ritchey-Chrétien astrographic reflector.
Your AT8RC is designed for coma-free imaging using DSLRs
and CCD cameras. It is particularly good with systems
involving long imaging equipment chains (CCD camera, filter
wheel, adaptive optics system, electric focuser, etc.)
These instruction sheets will provide you with information
on how to get the most out of your new Ritchey-Chrétien
reflector, and how to properly maintain your telescope so it
can give you a lifetime of quality imaging.
Please familiarize yourself with your astrograph’s parts and
functions before operating it for the first time.
astro-tech
AT 8 RC
from Astronomy Technologies
Lock knob
for focuser
drawtube
PARTS OF THE AT8RC
1.25” accessory
lock knob
Right coarse
focus knob
Fine
focus
knob
Mounting shoe for
optional finder
Locking collar for
removable 360°
rotatable focuser
Thread-on
extension
rings
Aperture
.................................................... 203mm (8”)
Focal Length
.................................................. 1625mm
Focal Ratio
............................................................... f/8
Optical Type
.............................. dual hyperbolic mirror
true Ritchey-Chrétien reflector
Mirrors
.......................... low thermal expansion quartz,
99% reflectivity dielectric multicoatings
Secondary Mirror Holder Obstruction
............. 95mm
(47% by diameter, 22% by area)
Field Stops
.................... ten internal knife-edge baffles
Tube Diameter
............................... 9.02” (229mm) o. d.
Tube Length
(without focuser)
................ 18.5” (470mm)
Tube Length
(with focuser)
....................... 22” (560mm)
Astro-Tech AT 8RC Ritchey-Chrétien Astrograph Specifications
Tube Weight
(without focuser)
........... 14.8 lbs. (6.73 kg)
Tube Weight
(with focuser)
................ 16.4 lbs. (7.45 kg)
Mounting System
........ one 15.5” Vixen-style dovetail,
one 15.5” Losmandy-style “D-plate” dovetail
Focuser
............ removable dual-speed linear Crayford
with 10:1 reduction ratio fine focus;
2” and 1.25” compression ring accessory holders;
360° rotating camera angle/observing angle adjuster
Focuser Mounting Thread
......... 90mm x 1mm metric
Focuser Travel
....................................... 1.97” (50mm)
Focuser Extension Rings
....... two 25mm, one 50mm
Finder
........ none; mounting shoe provided for optional
Astro-Tech multiple reticle finder or similar finder
Collimation
screws
Secondary mirror
holder and baffle
Vixen-style
dovetail
1.25” compression
ring accessory adapter
2” compression
ring accessory
holder
Drawtube
tension knob
(underneath)
Carbon fiber
tube
2” accessory
lock knob
Components of the Focusing System:
Your AT8RC has
a 2” Crayford focuser with a 2” compression ring accessory
holder on the focuser drawtube. There is also a separate 1.25”
compression ring accessory holder that can be slipped into
the drawtube’s 2” holder. These allow you to use either 1.25”
or 2” photographic accessories with no other adapters needed.
To minimize drawtube flexure under heavy loads during
imaging, the drawtube travel of the removable AT8RC fo-
cuser is kept short, at 50mm. To make up for the longer back
focus and lengthy all-purpose drawtube travel found in scopes
used both visually and for imaging (typically 80mm to 135mm
or more), the AT8RC focusing system has several compo-
nents, as shown in the illustration on the next page. They
consist of a removable 2” linear Crayford focuser that is
threaded onto the scope’s rear cell when you receive your
AT8RC and three thread-on extension rings (two 1” and one
2”). The rings can be installed singly or in combination be-
tween the focuser and the AT8RC’s rear cell. They provide a
flex-free solid metal focuser extension to take up any un-
needed back focus.
Left coarse
focus knob
Vixen-style
dovetail on
top of tube;
Losmandy-style
“D-plate”
dovetail
underneath
