Abstract: The invention concerns a very large optical telescope for observing light phenomena in the wave length region of about 0.3 to 30 or even to 300 .mu.m. To realize a very large filled aperture it is proposed to arrange comparatively few individual reflectors around a central monolith, which can be individually adjusted optically to the central monolith which gives the reference wave front, by means of an adjustment device and/or bright starts. In this way manufacturing, polishing and transport of very large primary reflectors can be handled. Further deformations due to wind loads, temperature variations and other influences can be easily compensated. The primary reflector is carried by a yoke with the focus of the secondary mirror being in or near the elevation axis so that the usual mirror cell becomes superfluous, the beam moves only slowly with elevation and heavy instrumentation can be put directly near the focus.