Abstract: A twin-etalon scanning spectrometer is disclosed that provides high luminosity and high resolution. The etalons are positioned in spaced relationship with respect to one another in series in the path of an emission light source. With identical etalons so positioned, a line emission transmitted by the rearwardly positioned etalon is at the same angles as that of the forwardly positioned etalon and the light transmission through the etalons is therefore at a maximum. When the relative spacing of the light transmission elements of one etalon is changed, however, the angles of transmission of the etalons are mismatched and the transmission of the light through the etalons is decreased until a minimum is reached when a .lambda./4 change in light transmission element spacing of one etalon relative to the other etalon has been effected.