"The Rolf refractor in Rathenow is a Schupmann-Medial telescope and therefore strictly speaking not a refractor, but a hybrid of mirror and lens telescope - at least that was the conceptual goal of Ludwig Schupmann (1899)." The Rathenow instrument is a Schupmann brachymedial Type B. The engineer and amateur astronomer Edwin Rolf has built it according to the concepts of Ludwig Schupmann.Until the construction of the Swedish Sun Observatory in 2002 on La Palma, it was the world's largest instrument of this type. " - de.wikipedia.org/wiki/Rathenower_Refraktor