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New Telescope Makes the Stars Wheelchair-Accessible

Photonics Spectra
Dec 1998
Daniel C. McCarthy

In the summer of 1995 the University of Illinois made many of its campus facilities wheelchair-accessible, including the observatory on the roof of the library. It wasn't until a year later, however, that wheelchair-bound visitors could participate in viewing the heavens with the aid of a fixed focal point telescope based on a coudé optical design and built by Optomechanics Research Inc. of Vail, Ariz.

Two achromatic lenses collimate light inside Optomechanic Research's modified Celestron 8-in. Schmidt-Cassegrain reflector. The first lens collimates the light, enabling the second lens to bring the image into focus at a special eyepiece tube assembly located at the fixed coudé position. The eyepiece tube can be adjusted to accommodate a variety of viewer positions. Courtesy of Optomechanic Research.

Coudé -- French for elbow -- signifies a telescope system that uses a series of mirrors to bring the focus to a fixed position. Coudé optics generally are used on large telescopes to send starlight to large stationary analyzing instruments. Their usage on the much smaller university telescope was intended instead to accommodate people who use wheelchairs, according to its designer, Ron Hilliard, president of Optomechanics Research.

"In a normal coudé system, they have to change optics in the optical tube to extend the focus to the coudé position. We were trying to not modify the optical tube because of the cost that would incur," said Hilliard. "So we kept the basic optics and added a couple of achromatic lenses."

The first lens collimates the light, allowing the second lens to be placed anywhere down the line to bring the image into focus at a special eyepiece tube assembly located at the fixed coudé position. To accommodate various viewer positions, the eyepiece tube adjusts from a nearly horizontal position upward to about 40° and can extend or retract by about 7 in. without losing image focus.

The optical tube is a modified Celestron 8-in. Schmidt-Cassegrain reflector. Hilliard said that the cost of the optical tube assembly -- usually a major factor in the total cost -- was a relatively minor expense in this instance. "We could build a telescope with a 14- or 16-in. tube assembly for not a lot more. Going to a 16-in. would not even double cost over an 8-in. tube and would improve viewers' ability to see fainter objects," he said.

Professor Charles Schweighauser, director of the observatory, said the new telescope was needed because of the popularity of his facility's Friday night "star parties." He since has set aside Sunday nights to allow up to 10 people who use wheelchairs and their companions to use the new telescope. "This technology's been around for a long time, but this is a new application," said Schweighauser.

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