Located in the original 16' dome adjacent to the IRT building is the 16", f20/f5 optical telescope. Set on a cross-axis english mount, this telescope was originally designed to be operated with a photoelectric photometer placed at the f/20 Cassegrain focus. It's convex secondary mirror is mounted such that it can be 'chopped' between different positions on the sky (the variable, sky, comparison, and then back to sky). This 'chopping' can occur fairly rapidly and, as a result, is termed the Rapid Alternating Detection System (RADS for short). The RADS allows for precise photometry even in light cirrus-filled skies, depending on the number of photons that penetrate the clouds.
With minor adjustments, the 'cass' secondary may be replaced with a Newtonian secondary thus yielding an f/5 focus. A Compuscope CCD camera is mounted at this focus yielding a field of about 7x12 arcminutes. Attached to the camera is a filter wheel sporting a complete set of Johnson UBVRI filters. With this configuration, the limiting magnitude for accurate photometry is about 13 and for detection is >15.
The possibilities with this new configuration have just begun to be explored. Recent targets have included the variable stars H235 in the openb cluster NGC 752 and the field contact system V728 Herculis. The following image is of Comet Hyakutake taken by Mike Mazur on the 41-cm Telescope:
Links to Related topics: Astronomical techniques