Wide-field collimators for spectrographs

This paper discusses various possibilities of collimators for wide-field fiber-fed spectroscopy, that would have good correction of oblique aberration. These possible collimators include a single mirror with some form of field correction (e.g., of Schmidt or Maksutov type), a two-mirror system of Cassegrain type, purely lenticular collimators, and collimators of the Maksutov form. It is shown that an off-axis Maksutov collimator is the best type for multifiber-fed wide field spectroscopy. Such a collimator can provide a highly corrected and obstruction-free alternative to the traditional off-axis paraboloid mirrors which are only suitable for spectroscopy of small objects. Optical data are presented of an f/11 and an f/6.5 off-axis Maksutov collimators.