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 of an 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 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.
Since then age has taken its toll on this system and in 2013 the
observatory has launched another major tune-up for the telescope.
Funding for this project was provided by former Butler physics
student Dr. Frank Levinson through the Silicon Valley Community
Foundation. The $325,000 of funding will allow us to bring the
telescope into the 21st century to better suit the needs of our
students and faculty along with keeping James Holcomb's original
intent for the observatory, our continuing tradition of educating
the public about the cosmos. For more information and the present
state of the upgrade visit the link at the bottom left.