Abstract: An optical arrangement for use in spectrometry uses a masking device which eliminates unwanted spectral regions prior to optically resolving the unmasked information. The optical arrangement comprises an entrance slit to select incidence spectral energy from an energized source and a concave grating of relatively low dispersion to image the spectrum of the entrance slit onto a stationary mask which simultaneously selects spectral regions of the dispersed incident spectral energy. The selected spectral regions are collimated and recombined and directed onto an Echelle grating to disperse with high resolution the selected spectral regions. A concave mirror focuses the dispersed selected spectral regions into a focal plane of highly resolved spectral energy which can be detected to determine the spectral information coming from the source. The optical arrangement is particularly well suited for use with narrow spectral bandwidth spectral information distributed over a large spectral range.