We present a new design of a Fabry-Pe´rot interferometer for Brillouin spectroscopy. Emphasis is placed on a quick change of the free spectral range without losing alignment, the possibility of switching the multipass arrangement from 3 to 5 pass and back, and finally on a simple and inexpensive construction. Besides this the new interferometer shows very good long term stability and is easy to handle. These features were not available before in this combination. The performance of the instrument will be demonstrated. ©1997 American Institute of Physics.