RCOS 14.5" Telescope

The centerpiece and workhorse of the observatory is the 14.5" RCOS telescope. In addition, there are a variety of components — some to extend its viewing capabilities, some to collect data, and some to control its various functions.

The telescope is a 14.5" f/9 Ritchey-Chrétien telescope built by RC Optical Systems.


The telescope has a focal ratio of f/9, a mirror diameter of 368 mm (14.5"), and a focal length of 3315 mm (130"). Our theoretical angular resolution is 0.31 arcseconds of separation.

The magnification and field of view (FOV) depends upon the attached eyepiece.

Eyepiece Magnification FOV
31mm x107 46 arcmin
20mm x166 30 arcmin
12mm x276 18 arcmin

For comparison, the angular size of the Moon is about 30 arcmin (or ½°).

Ritchey-Chrétien Telescope (RCT)

The Ritchey-Chrétien telescope (or RCT) is a specialized Cassegrain telescope designed to eliminate coma, thus providing a relatively large field of view as compared to a more conventional configuration. An RCT has a hyperbolic primary and a hyperbolic secondary mirror. It was invented in the early 1910s by American astronomer George Willis Ritchey and French astronomer Henri Chrétien.

The Ritchey-Chrétien design is free of third-order coma and spherical aberration. When focused midway between the sagittal and tangential focusing planes, stars are imaged as circles, making the RCT well suited for wide field and photographic observations. As with the other Cassegrain-configuration reflectors, the RCT has a very short optical tube assembly and compact design for a given focal length. The RCT offers good off-axis optical performance, but examples are relatively rare due to the high cost of hyperbolic primary mirror fabrication; Ritchey-Chrétien configurations are most commonly found on high-performance professional telescopes.

The 2.4m Hubble Space Telescope is an RCT.