DBS Overview

The Dual-Beam Spectrograph is a general purpose optical spectrograph, permanently mounted at the Nasmyth A focus of the ANU 2·3m telescope. The visible waveband (3200 - 9000) is split by a dichroic at around 6000 and feeds two essentially similar spectrographs, with red and blue optimised detectors respectively. The full slit length is 6·7arcmin. Gratings are available with rulings of 158 to 1200 lpmm, giving dispersions of between 4 and 0·6 Å/pixel. The 1200B grating may be used in second order to give 0·3 Å/pixel over the range 3200 - 5000Å. The dichroic may be removed or replaced with a flat mirror allowing the use of either arm independently.

Other possible instrument configurations include replacement of the slit with a slitlet aperture plate (up to thirty objects over 6 arcmin) and replacing the gratings with plane mirrors, converting the spectrograph into a focal reducer that images the 6·7 arcmin field at f/1·5.

Assorted useful numbers:
The DBS is at Nasmyth A focus.
Telescope scale is 5·02 "/mm and the f/ratio is 17·9.
The unvignetted field of the telescope and slit is 80 mm or 6·7 arcmin
The collimator focal length is 2812 mm and the camera focal length is 232 mm
The beam is 152 mm.
The cameras are f/1·5 so the imaging scale is about 1 arcsec/mm.
The camera/collimator ratio is 12 and the angle is 32 deg.
Across dispersion, 0·015 pixel = 0·91 arcsec.

References:
A Dual-Beam Nasmyth Spectrograph, A.W. Rodgers, P. Conroy, G. Bloxham, 1988, PASP, 100, 626
Get a copy from ADS.

Many thanks to those who contributed to this documentation:
The Teldocs Consortium, Saskia Besier, Mike Bessell, Michelle Buxton, Paul Francis, Ken Freeman, Lisa Germany, David Hoadley, Helen Johnston, Lisa Kewley, Joe Liske, Sean Ryan, Elaine Sadler, Raylee Stathakis, Wilfred Walsh.

Last modified: Tue Jan 25 12:48:07 EST 2000