DCT is a Ritchey-Chretien telescope with powerful instrumental capability at its focal plane.

The DCT employs what is called a Ritchey-Chretien optical design. Light enters the telescope through the dome slit and is reflected off the 4.3-meter primary mirror, which is figured into a concave hyperbola with a precision of 50 to 75 nanometers at all spatial scales across the mirror.  The light then reflects off the 1.4-meter secondary mirror, which is a convex hyperbola.  It then returns through a hole in the center of the primary mirror and arrives at the focal plane.  This configuration provides a large, stable field of view for the instruments mounted to the back of the telescope.

The RC instrument cube

The instrument cube is one of DCT’s greatest strengths.  One face of the cube is bolted to the back of the mirror support cell.  The other five faces can each accommodate a different instrument that our astronomers can use to carry out a large variety of programs. Deployable fold mirrors inside the cube allow fast switching between instruments mounted at the various ports. DCT users therefore can conduct programs requiring near-simultaneous imaging and optical / near-infrared spectroscopy.

This ability to switch instruments in about one minute – rather than the hours required to physically remove instruments and bolt new ones to the telescope – led former Lowell Director Bob Millis to describe DCT as a “Swiss Army Knife of telescopes.”  DCT researchers will use this capability to powerful advantage in years to come.

The cube was designed by Lowell Observatory instrument technicians and engineers including Tom Bida, Ralph Nye, and Ted Dunham.  Most of it was machined and assembled in our instrument shop, while some parts were outsourced, including to the Scientific Instrument Facility (SIF) at Boston University.


As of February 2015, two instruments are present on the cube: the Large Monolithic Imager (LMI) and the DeVeny spectrograph.

In the near future, DCT will get infrared spectroscopic capability via NIHTS, the Near-Infrared High-Throughput Spectrograph.  Additional capabilities will be provided by an instrument called RIMAS, the Rapid Infrared IMAger-Spectrometer, now under development at the Goddard Space Flight Center.

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