The 24-inch (0.6-meter) Ritchie-Chretien research telescope was manufactured by RC Optical Systems and installed in August 2006. The instrument features a very robust fork mounting with an absolute Renishaw precision encoder on the polar axis. It is capable of pointing with second-of-arc precision from a cold start under control of a version of XmTel including corrections for polar alignment.
The telescope's Zerodur optics were made by Paul Jones of Star Instruments. The f/8 system has a peak-to-valley wavefront variation of 0.242 wave, and 0.039 RMS, with a Strehl Ratio of 0.941. The mirrors have an Spectrum Coatings enhanced aluminum coating with a reflectivity peaking at 96.9% at 528 nm, decreasing slightly to 95.7% at 450 and 650 nm. With efficient well-corrected optics useful from the atmospheric UV cutoff below 380 nm through the near infrared above 2 microns, the 0.18 arcsecond diffraction is achievable for visible light with very short exposure times to minimize atmospheric turbulence.
The instrument is focussed by a precision adjustment of the secondary mirror to bring the focal plane into coincidence with a fixed focal position 255 mm from the back of the primary mirror cell. Spacers are used to put the camera or other instruments at the proper position, and an encoded focus motor moves the focal plane 5 microns per encoder count. The image scale in the focal plane is 42.3 arcseconds/mm, so that 1 arcsecond corresponds to approximately 24 microns. At f/8, the telescope can focus precisely to within its diffraction limit since the least count on the focus encoder translates to a image size for a point source of 0.026 arcseconds. In long exposure imaging with averaging seeing of 1 arcsecond, focusing precision of 40 encoder counts is typical. A focal plane corrector and instrument rotator will be added in the summer of 2007.
The telescope is presently being tested with three cameras:
The RC24 photo gallery has more views of the telescope and its instrumentation.
