Published online by Cambridge University Press: 12 April 2016
Focal reducers provide efficient solutions to the drawbacks introduced by the large focal length of direct foci on large modern telescopes. They house a variety of spectroscopic devices, and lead to various families of spectroimagers. Rational filterings, BPM irmltisimultaneous bandwidths, extreme spectral resolution of the field scanner interferometers (Tully’s first design, Taurus, Cigale) and their image reconstruction, as well as the possibility to obtain the spectra of all image elements of the field owing to the new (Tiger and Silfid) integral field spectrographs sometimes combined with Fabry Perot Interferometers (Pytheas) are now within reach. In classical spectrography the focal reducer leads to the optimized size Baranne’s white pupil spectrograph.