Spectrally filtering at least one input beam includes dispersing spectral components of at least one input beam at different respective angles in a spectral plane; changing at least some of the angles of the propagation axes of the dispersed spectral components so that the maximum angular separation among the propagation axes of the spectral components changes; receiving a plurality of the dispersed spectral components incident on a reflective surface at a location at which the central rays of each of the spectral components are incident at different points on the reflective surface; and tilting the reflective surface to select at least one and fewer than all of the received spectral components to be directed to a selected output path.