Abstract: An apparatus for applying a load to an etalon so as to enable the accurate tuning of desired frequencies or ranges of frequencies. The invention includes first and second optical surfaces separated and disposed highly parallel with respect to each other by an electric longitudinal spacer member. A biasing means applies a longitudinal load to the elastic longitudinal spacer member. The applied load is uniformly distributed throughout the spacer member by a longitudinal load distribution means, which is disposed between said biasing means and at least one of said optical surfaces. The distance, d, between the first and second optical surface is directly proportional to the load applied by the biasing means. The load may be varied, in one embodiment of the invention, using a bias adjustment means acting in mechanical cooperation with the biasing means.