Anamorphic Magnification of Grating Spectrographs - A Reminder

Abstract

Attention is called to the long-known; but often ignored; property of a grating spectrograph to (de)magnify the slit width and length by different amounts. As an illustration; the "grating magnification" r is given as a function of grating tilt for the Ritchey-Chretien spectrograph of the CTIO 4-meter telescope; we find that for large grating tilts the spectrograph slit can be opened to more than twice the usual width. This results in significantly more star light going down the slit in average seeing.