An imaging catadioptric spectrometer using a Mangin type lens and pupil lens adjacent to a grating. Electromagnetic radiation received by aperture slits is directed to a reflective portion of a Mangin type lens and redirected to a pupil adjacent a diffraction grating. Diffracted light is transmitted through a refractive portion of the Mangin type lens and through a corrector lens to image the spectral components of electromagnetic radiation onto a detector. The detector may be an enhanced detector utilizing an array of smaller spaced detectors. By balancing the powers of the lens elements, a single optical material may be used. In one embodiment, multiple aperture slits are spaced apart and decentered with respect to the optical axis permitting collection of opposing diffraction orders on two detectors. A wide field of view having a low F number is obtained with an operating wavelength range in the infrared from approximately 7.5 to 13.5 microns. The spectrometer is particularly suited to airborne applications.