WO Equipment

The Observatory's primary telescope is a 0.41 m (16 inch) f/8.4 RCOS carbon-truss Ritchey-Chrétien reflector, mounted on an Astro-Physics 1200 GTO heavy-duty German equatorial mount. This is supported by a 300 mm diameter steel pier, 12.5 mm thick, embedded in a 900 mm square concrete block reaching 1.5 m into the ground. This has not moved since it was placed there, by more than a few arcseconds. The telescope has a temperature-compensating focuser operating on the secondary mirror, and together with the carbon-fibre construction I find no need to refocus as temperatures plunge overnight, or indeed from night to night.
Mount control is from MaxIm, MaxPoint, PinPoint and TheSky working jointly through ASCOM's Plain Old Telescope Hub. Aside from other things, this provides automatic meridian flip with image recentering, and astrometrically based tracking. Even with tracking turned off, there is no discernible drift in a 4-minute image. Slewing is accurate to about 4 arcmin.
Telescope control is via the RCOS Telescope Command Center which handles thermostatically controlled secondary heating and primary cooling, temperature-controlled focus adjustment, and precision image rotation. Focusing is done automatically via FocusMax, which takes little time and just needs a 9th magnitude star.

The primary science instrument is an Apogee U13 CCD camera, shown in the picture opposite. It has 16 micron pixels in a 1280 by 1024 array. This gives an image of 21 x 17 arcmin, with 1.0 arcsecond per pixel. The camera is connected to the observatory's computer (which is one node of the household's LAN) by an active USB 2.0 cable, giving a full-frame 16-bit download time of 1.8 s.
In the instrumentation train, first comes the RCOS Precision Instrument Rotator, then an Optec filter wheel with Johnson-Cousins B V Rc Ic and clear filters. Next is a Van Slyke Slider, modified to remove vignetting by the pickoff mirror, and wrapped here and there in black felt to remove light leaks. Finally comes the camera.
The observatory also has a fast low-light webcam with GPS-based time-stamping equipment, to be used (in the eyepiece position) for occultation timing. This instrument is not yet fully operational - I'll provide more data on it when it is.

A separate control room is very important. Aside from providing a good workspace, warmth and comfort, it keeps stray light away from the telescope. One difficulty with an open truss design of telescope is that ambient light from within the telescope room can easily reach the downward-facing secondary mirror, and by illuminating dust on it contaminate a camera image.

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