Refractive elements in spectrographs

A spectrograph design was needed for an application in medial optics. Requirements for resolution were modest, cost was to be minimized, and every photon was precious. The initial design used a concave, aberration-corrected, holographically-recorded, diffraction grating. This design cost too much and collected too few of the precious photons. Several design forms, which use refractive optics with a planar diffraction grating, were investigated. The design that was chosen and built uses two aspheric glass lenses, one for collimating and one for focusing, together with a planar diffraction grating.