Specifications for the Observatory Telescope & Mount
Ritchey-Chretien 20" f/8.1 Telescope
using hyperbolic figured 20" primary and 7.25"
secondary lightweight conical shaped low expansion
The mirrors will be aluminized and covered
with a protective coating that meets or exceeds milspec
MIL-M-13508C for resistance to abrasion and corrosion.
The reflectance (for a single reflection)
will be as flat as possible in the wavelength range from
400 nm to 750 nm, with a maximum value of at least 95%
and a minimum of no less than 90%. From 750 nm to 1000 nm
the reflectance should be no less than 80%.
The optical system will be diffraction
limited, having a final wave front error of 1/4 PV and
A Zygo interferogram with fringe analysis
will be provided to certify the optical quality of the
The mirrors will be mounted in a closed
painted 6061T-6 aluminum tube with anodized aluminum
components and stainless steel fasteners to resist
corrosion and minimize infrared scatter.
A sealing mirror cover will be provided.
Both mirrors will be held rigidly while
allowing for differential coefficients of expansion
between the mirror and mount.
Optical collimation adjustment screws are
widely spaced, providing fine adjustment and secure
A electronic, stepper motor controlled
secondary focuser will be provided and designed so that
the focus is stable during a change in instrument
Boresight stability will be ± 20
arcseconds regardless of telescope orientation.
The telescope assembly will be equipped
with slewing handles.
Threaded holes, will be provided on the
back plate,for instrumentation attachment.
Full length counter-weights on both sides
will facilitate symmetrical, fine balancing of the
Included with the scope will be a 11 X 80
illuminated finder telescope with a Polaris reticule, a
tube attachment fixture, clamping rings, a 2" star
diagonal and a 55mm Tele Vue eyepiece.
OGS140 Equatorial Fork Mount:
Equatorial fork mount for telescope to be
constructed of precision machined aluminum and stainless
steel alloys with axles of 6" O.D..
The axes of the mount will be orthogonal
to better than one arc minute.
The mount will have an equipment capacity
of at least 290 pounds.
The clearance between the telescope
backplate and the fork top surface will accommodate a
swing-through of at least 18 inches.
Both axle drives will include Byers gears
with a 18" gear on the Right Ascension axis, slip
clutches, negligible backlash between the worm and worm
wheel, ABEC7 pre-loaded ball bearings to support the worm
shaft, and a beam coupling to connect the drive motor to
the worm drive providing anti-backlash, constant velocity
power transmission and vibration damping.
The telescope optical axes will be aligned
with the mount axes to within 1 arcminute and the
combined system will be capable of tracking objects with
an accuracy of less than 3 arc second periodic error
without the need for computer correction.
The mount will be set for a latitude of 30
degrees, 23 minutes and include fine adjustment for
azimuth and elevation.
Computer Control System:
The computer controlled telescope system
consists of software capable of providing telescope
focusing, slewing, tracking, and dome control as well as
the electronic interface to the telescope, mount and
A Pentium computer with monitor, keyboard
and mouse, compatible with the software and electronics,
will be supplied to provide the direct user interface as
well as the interface to a remote control system.
All motors, sensors, cabling and
interfaces will be provided and the system will be
compatible with an existing Ash Dome (model 22.5' MEBH).
The slewing motor speed will be adjustable
so that the telescope can be quickly positioned and then
accurately centered on an object.
The tracking motor speed will be
adjustable and provide sidereal, lunar, solar, cometary,
asteroidal and user definable tracking rates.
A control paddle will control the speed
(guide, drift, slew) on the drives and direction (all
cardinal directions) of the telescope motion independent
of the computer keyboard.
The system will be capable of compensating
for an object's proper motions, the effects of
precession, nutation, annual aberration, atmospheric
refraction and parallax as well as for
mechanical/optical/polar misalignment and periodic error.
This compensation enables the telescope to
be positioned on any object in the full sky to within ±
30 arcseconds RMS and to track the object over 20 minutes
of time to less than 1 arcsecond of error.
Dome control includes dome rotation and
shutter open / close operations along with manual
A "rain sensor" signal will be
supplied by LSU and will be used in the software to veto
the shutter open operation and to automatically close the
shutter during remote operations.
Finally, all control functions, readouts
and displays, with the exception of configuration and
calibration operations, should be accessible over a T1
internet link and should be capable of using software
such as TheSky as the user interface.
Last updated by Frederick J. Barnett on Thursday, January 20, 2005 11:48:09 AM