Abstract

A basic relation connecting the final camera focal ratio to the grating constant, the pixel width, and the spectral resolution of a CCD spectrograph is given. The Rosendahl "coscubed" condition for zero meridianal coma in Czerny–Turner systems is extended, and the coma and astigmatism as functions of the field angle are derived. A condition is derived for obtaining the spectrum on a flat field normal to the outgoing chief ray. This condition allows a focal reducer to be coupled directly to the spectrograph output, and a suitable design for a focal reducer is outlined. The final spectrum is then captured by a standard 35 mm camera lens of suitable quality and aperture. A spectrograph based on these criteria has been built and is being used to explore the spectrum of the night air glow at a resolution of 0.4 A in the visible. Examples of spectra obtained will be shown.

© 1992 Optical Society of America