Abstract: A scanner having an instantaneous narrow field of view determines spectral and positional information of a point source of optical radiation in a relatively wide field of view. A first optical path includes the scanning means, a dispersion means, and a first detector means so that different wavelengths of the source are convoluted to impinge on the first detector means at different times during a scan of the field of view. A second optical path includes the scanning means, the second detector means, and a narrow bandpass filter for enabling approximately monochromatic energy of the source to impinge on a second detector means displaced from the first detector means. Thereby, a predetermined wavelength is imaged on the second detector means at a time during a scan that differs from the time when that wavelength is imaged on the first detector means, even though the source angular position in the field of view is substantially the same for both of the optical paths.