A beamsplitter includes a bifurcated frame, which rotates about a vertical axis, enabling the transmissive properties of an optical element, e.g. etalon, mounted on one arm of the frame, to be tuned as the angle of the optical element is rotated relative to an incoming optical beam. A mirror is mounted on the other arm of the frame intersecting light reflected from the optical element and redirecting the reflected light along a path, which is constant relative to the incoming optical beam.