Allen Telescope

The Allen telescope is a 24-inch reflecting telescope of Ritchey-Chretien design, named in honour of Professor C. W. Allen, the first Perren Professor of Astronomy at University College London (1951–1972). The telescope was inaugurated by Professor D. W. N. Stibbs, Napier Professor of Astronomy at the University of St. Andrews, on 1975 May 22. It was acquired at a cost of £42000 pounds to replace the original 'Wilson telescope'. donated to UCL in 1925 by Mr. J. G. Wilson (the building is still referred to as 'the Wilson building').

 

Arc spectra for the Allen spectrograph

Built/acquired:	1974/5
Refurbished:	1991, 1998
Optics:	Ritchey&ndash&Chretien Reflector
Aperture:	24" (600mm)
Focal Length:	276" (7000mm)
Detector:	Apogee Alta U47 16bit CCD, 1024x1024 array, 13x13 micron pixels
Additional Instrumentation:	Cassegrain Spectrograph
Field of view:	55 arcmin (not used imaging)
Controls:	Digital GoTo
Drive:	DC servomotors (DFM Engineering)
Mount:	German Equatorial

Description

Like most reflecting telescopes, the Allen consists of two mirrors, the primary and the secondary, separated by the main tube of the telescope. The light enters the telescope and is focussed by a correctly shaped concave mirror. This primary mirror is polished precisely into a paraboloidal surface, since this is the only surface which will focus parallel rays to a point. The two mirrors are covered with a highly reflective layer of aluminium, which is applied using a vacuum deposition technique. The secondary mirror is included to provide a longer focal length and more convenient observing position. The secondary has a convex hyperboloidal profile, and intercepts and reflects the cone of converging rays back through a hole in the primary. The telescope's focus is located a short distance behind the hole, as with all Cassegrainian designs. Accurate focussing of the Allen telescope is accomplished by moving the secondary mirror a small amount using an electric motor.

The main use of the telescope is for the instruction of students at UCL. The telescope itself acts as a light collector for a Cassegrain spectrograph with CCD camera, used to obtain spectroscopic observations of stars, nebulae, novae, etc. The telescope can be operated within the dome or remotely from a control room, as is the practice at professional observatories worldwide.

Refurbishment

Constructed in 1974, the Allen telescope's electronics and drive were replaced in a 1991 with a new computer-controlled system, designed and installed by DFM Engineering of Longmont, Colorado, USA. It was upgraded again in 1998, with a new control system, also designed and installed by DFM Engineering.