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The Telescopes

The 6-inch Refractor

Butler University's first telescope was a 6-inch refractor donated to the University in the late 1880s when the campus was located in Irvington on the east side of Indianapolis. The 6-inch refractor can be seen in the image to the left. It is the long telescope riding piggyback on the 38-inch telescope. A refracting telescope uses a lens to gather light. This light is then focused at the back of the telescope where the observer looks through the eyepiece.

When Butler University moved to its current location in1927 the 6-inch telescope was used on top of Jordan Hall. Once Holcomb Observatory was built in 1954, this telescope was put onto the 38-inch Cassegrain telescope as a spotting/wide field telescope. The telescope is still in good operating condition and now serves as our guide scope using a CCD camera.

The 38-inch Cassegrain

The main telescope in use at Holcomb Observatory is the 38-inch Cassegrain. This telescope along with the observatory was built in 1954. A Frenchman, Nicolas Cassegrain (1625-1712), invented this two mirror telescope. Almost all modern telescopes follow this basic form to some degree. The diagram below illustrates the optical elements and the path that light takes through the telescope. The primary mirror has a parabolic shape and gathers light in the same way a refractor gathers light using its objective lens. The secondary mirror, an hyperbolic shape, reflects the light back through a hole in the primary mirror. The instruments and eyepiece are located near the focus behind the telescope.

Though the 38-inch Cassegrain is structurally and mechanically sound it was initially difficult for the observer to use. In order to go from object to object the observer had to physically move the large telescope by hand. In addition after many years of addition and subtraction of equipment the telescope was grossly out of balance and years of wear and tear made the telescope's tracking suspect. With the advent of students using CCDs for data acquisition it became apparent that the telescope should be automated and incorporate precession tracking and positioning via a computer. This automation would allow students to more easily acquire targets and data making observing sessions a more pleasant learning/research experience.

In 1994 Butler University began the first phases to upgrade the 38-inch telescope. Upgrading the large telescope proved a significant challenge for the university. The university hired AB Engineering of Ft. Wayne, Indiana for the upgrade. They proposed a retrofit of the mount with computer controlled polar and declination axis drives. This project required the replacement of the original polar axis worm with a new precision worm assembly and the declination tangent arm with a 26-inch diameter worm gear set. Each axis is driven by a single stepper motor providing both tracking and slewing operation. The encoders and stepper motors are controlled by a Telescope Control Computer in the telescope dome. A dedicated, solid state controller orchestrates motion control and position monitoring. The telescope's position is displayed via digital setting circles on a large character LED display, mounted on the wall of the observatory and on Software Bisques' The SkyTM via a virtual RS-232 connection or the local area network. An integrated GPS receiver provides time and location initialization. Operator control of the telescope is through a hand-held paddle or through a PC via the Internet. A motion warning system notifies personnel within the observatory when the telescope is slewing and when slew limits are being approached.

The upgrade highlights included:

• Motorization of both the Polar and Declination axis to accommodate variable tracking and slewing operation
• Optical encoders provide polar and declination position feedback via digital setting circles
• Passive free weights to eliminate gear backlash.
• Computerized user interface for operation of the telescope (remote and in dome)
• Dome automation and coupling to the telescope motion
• Primary telescope CCD and imaging and autoguiding
• Addition of an mirror cover
• Automated GOTO software with synchronized dome control
• Precision pointing using Tpoint
• Remote access via the Intranet
• Scripting for robotic control

The first phase of refurbished telescope was finished in April 1997 and commenced operation, with Mr. Tom Bopp, co-discoverer of comet Hale-Bopp, presiding. In 2001 the final automation was completed. The telescope is now fully automated so that it can be run robotically and remotely and carry out an single night's observing program unattended.