07/02/06

Instrumentation used at the Francisquito Observatory is typical for a facility specializing in NEA confirmation and follow-up observations.  In keeping with the spirit of our .ORG web site designation, we will avoid mention or discussion of specific models or makers of hardware and software (with the exception of freeware or shareware).  However, we'd be happy to discuss any aspect of our facility, including specifics on hardware and software, via e-mail.  Send inquiries to: director@nospam.francisquito.org  Additionally, we hereby give our permission to any suppliers or manufacturers of hardware and software in use at Francisquito to make reference to pages on this web site if they so desire.

MECHANICAL AND OPTICAL SYSTEMS

The Francisquito Observatory utilizes two telescopes, which are attached to a single, computer-controlled equatorial mount.  The equatorial mount comfortably handles the combined load of two telescopes.  The mount currently has a polar alignment that is within 2 arc-min. of the Earth's polar axis.  It can track with good precision for about 90 seconds before autoguiding might be contemplated.  With pointing correction software activated, it consistently points to within 0.3 arc-min throughout a typical observing session.

The primary telescope used for astrometric observations is a 30cm diameter reflecting telescope of Schmidt-Cassegrain design.  This telescope has a native focal length of 3000mm, but is used in conjunction with a CCD unit that has a 0.67x focal length reducer/field flattener made specifically for its CCD chip, and which is attached directly to the CCD unit.  This yields an effective focal length of 2000mm.  The shorter focal length yields a wider field of view and shorter exposure times for the CCD unit.  From a purely astro-photography point of view, the optical performance of the 30cm reflecting telescope is mediocre at best.  However, it delivers completely satisfactory performance as a large aperture light collector for NEA observations.   For this type of work, the performance/cost ratio is in fact quite high.

The second telescope in use is a 9cm diameter, APO refractor.  It has a native focal length of 500mm, but is also used at times with a focal reducer/field flattener that yields an effective focal length of about 400mm.  This telescope is used in conjunction with a second CCD unit as a dedicated autoguider for longer exposures through the main telescope.  It is also used for visual observations, and is superb for CCD-based astro-photography.  Looking through this telescope at clusters of bright stars or a colorful star pair like Albireo is absolutely breathtaking.

MAIN CCD UNIT AND FOCUSER

The CCD imager at Francisquito is the real workhorse of the observatory.  It typically takes 200 to 300 images per observing session.  The CCD chip has a 2184x1472 pixel array and a native 6.8 micron pixel size.  The CCD chip is exceptionally light sensitive for a non-backlit design, reaching a peak quantum efficiency of 85% around the visible-red portion of the electromagnetic spectrum.  During cool weather the CCD chip temperature is kept at about -20 degrees C by the on-board thermoelectric cooler.  During warm summertime temperatures the CCD chip temperature is lowered an additional 5 degrees C by means of a liquid coolant system, though the typical summertime CCD temperature is still as high as -15 degrees C with liquid-assisted cooling.  The individual pixels on this CCD chip can be grouped (binned) into clusters of 4 (2x2) or 9 (3x3) pixels to form 'super-pixels' of even greater light sensitivity.  Using this CCD unit at a 2000mm focal length and 3x3 pixel grouping (yielding 20.4 micron super-pixels) brings the telescope/CCD combination to the dead center of the NEA astrometry "sweet spot" of 2.0 arc-seconds of sky coverage per pixel.  All astrometric observations at the Francisquito Observatory are made with the CCD unit set to 3x3 pixel grouping.  Under good sky conditions at Francisquito, the CCD unit can reach down to magnitude 18.5 for a single 2 minute exposure of a slow moving asteroid.  On one exceptionally dark and clear night at Francisquito, the CCD unit reached magnitude 19.0 for single 2 minute exposures of NEA 2004HH33

The CCD unit is mounted directly to a computer-controlled focuser, which is in turn mounted to the back of the reflector telescope.  At the beginning of each observing session the CCD unit is initially brought to focus using a software tool called FocusMax (described in the next section) and then set to Temperature Compensating Mode.  The focuser has been pre-calibrated with the main telescope to monitor the telescope's temperature and then adjust the focus throughout the observing session to compensate for changes in the telescope temperature.

SOFTWARE

The Francisquito Observatory uses a number of software tools to get its work done.  One software package controls the telescope and CCD unit through pre-written observing session scripts, as well as making continuous improvements to its pointing correction model.  Once an observing session script has been initiated, the telescope will work through the night until its pre-programmed tasks are completed, after which the telescope parks itself and shuts down the CCD unit.  Another pair of software packages are used to perform the actual astrometry on CCD images containing asteroids.  One of the two astrometry packages, Astrometrica, is available as shareware; it is particularly useful for fast moving asteroids when many, short exposures are the only feasible way to get good astrometric solutions for the asteroid's position.  The focuser is controlled by a freeware tool called FocusMax; it can bring the CCD unit to a sharp focus in as little as 30 seconds.

PUTTING IT ALL TOGETHER

Someone not familiar with the demands of running a science-grade observatory may be inclined to think that all this cool technology would make it easy to achieve quality results.  The reality is, that making all the hardware and software work together for the duration of an observing session can be a real challenge.  As an example, consider the Francisquito Observatory's start-up checklist.  Preparing the observatory for an evening of NEA data collection is not a simple matter of switching on the power and then pointing the telescope in the right direction.  Running through the start-up procedure takes anywhere from 30-45 minutes if no significant problems are encountered.  If a step in the checklist is accidentally left out, or in some cases, not executed in the proper order, then an entire evening's worth of data can end up being useless.  An example start-up checklist from a typical observing session is reproduced here.