Spectrometer device (100) with entrance aperture (2), diffraction grating (3), two detectors (5a, 5b) to spectrally measuring the incoming light (L), the detectors being located on the same side of the dispersion plane. Two vertically focusing mirrors (4, 4a, 4b) focus the light onto detectors, the minors being arranged as front row mirrors (4b) and back row minors (4a) along two polygon graphs (6a, 6b) offset to each other and to the focal curve. The angles of deflection (cp, 91) for the front row mirrors are