Abstract: A mirror is provided having an adjustable focal length. The mirror includes a tubular frame in which is mounted a pair of end walls, either one or both of which may be transparent, and an internal, flexible wall that divides the frame member into two separate chambers. Where one transparent end wall is provided, the flexible, internal wall has a single reflecting surface in opposition thereto. Where two transparent end walls are provided, the flexible internal wall has two oppositely facing reflecting surfaces. A conduit provides direct communication between both chambers and a reversible pump is in communication with said conduit for selectively producing controllable pressures in the two chambers.