Some Schiefspiegler History

Anton Kutter (1903-1985) tells the story of the developments to the Schiefspiegler in the introduction to his 1953 book, Der Schiefspiegler (Kutter 1953), as follows:

Already in 1685, only 23 years after Gregory's and 13 years after Cassegrain's classical publications of their telescope construction concepts, a father J. Zahn published a construction plan which almost resembles a Schiefspiegler, and particularly emphasizes on the advantage of a primary mirror without a hole. Unfortunately, it is not known if at that time any optician tried to construct a telescope from these plans.

Kutter does not mention, and was probably not aware of, the experiments of 1616 by Nicolas Zucchi or latinized Nicholaus Zucchius (1586-1670), only about a decade after the first refracting telescope had been constructed in the Netherlands. Zucchius used a single concave mirror, tilted to avoid massive obstruction by the observer, and an eyepiece as telescope. His short instruments suffered heavily from astigmatism and produced only bad images.

Zucchi's construction was occasionally put up in 1732 by French astronomer Jacques Lemaire without notable success.

In the 1780s, William Herschel used a tilted, oblique primary mirror for his giant telescope constructions; this Herschelian concept was apparently the first successful realisation of telescope with leaning mirrors: His 18.7-inch f/12.6, 20-foot FL reflector which was used for most of his nebula observations, and his giant 48-inch f/10, 40-foot FL giant telescope. Herschelian telescopes were commercially produced in the 1830s e.g. by Amasa Holcomb of Southwick, Massachusetts, with apertures of of 4 to 6 inches.

Next, in 1808, Berlin astronomer Johann Elert Bode proposed to connect the Herschelian concept of a tilted mirror with that of Cassegrain, in order to avoid a perforated primary mirror (Bode 1808). Again it appears that contemporary astronomers and opticians did not pick up this idea for any construction endeavors.

Hugo Schröder reported in the late 19th century that a British inventor picked up the idea of an "excentric reflecting telescope," but that still did not lead to a new telescope construction.

Only in 1876-77, Vienna opticians J. Forster and Karl Fritsch developed an excentric Cassegrain telescope which they obtained an Austrian patent, and called it the Brachy Telescope (translated "Short Telescope"). Anton Kutter criticizes that name as actually a Brachyt is at least slightly longer than a Cassegrain of the same aperture and effective focal length. Brachy telescopes were sold in comparatively small number until at least 1912, in standard apertures of 106 mm (4-inch) and 160 mm (6.3-inch), but also some 8-inch and at least one 32-cm (12.6-inch), which was sold to the Naval Observatory of Pola about 1880. Kutter reports that this instument had such bad references that the lunar and planetary specialist, Philip Fauth, rejected to accept it as a present offered to him. Brachy telescopes had their friends among other telescope makers of the late 19th century, notably the Hungarian nobleman Nicolaus von Konkoly-Thege.

Kutter got his informations about the Brachyt from Anton Staus, who had used one of 10-cm aperture in his younger years, and was delighted of the performance of that instrument. Nevertheless, the Brachyt construction of Forster and Fritsch suffered from the fact that its coma could only be limited if some non-central obstruction at the limb of the primary mirror.

Apparently, Kutter was not aware of an idea and experiments of Andrew Ainslie Common (1841-1903), a pioneer of astrophotography, published in 1895 (Common 1895a), but going back to before 1886, of a modified Cassegrain with tilted mirrors, in such a way that obstruction won't occur any more. Common reports to have experimented with this construction with some success. Confronted with the earlier Brachyt of Fritsch and Forster, which he had not been aware of, Common mentions an earlier discussion on similar telescope concepts (Common 1895b): In 1884, in the English Mechanic, Mr. W.R. Brooks had described one which he requested to be called the "Brooks Reflector." In response, a Mr. Coates of Manchester wrote to the same periodical, that a similar telescope had been described in a book he possessed, published in 1825 by Fisher in London, and entitled The Panorama of Art.

In 1936, Anton Kutter succeeded in arranging with the optical-mechanical workshop of Georg Tremel, the successor of Merz Optics in Munich, to develop a capable amateur telescope. Merz optics had come into contact with the Brachyt design in 1918, when one such instrument had been turned for repair to Paul Zschokke, the workshop's owner at that time. In the following, Zschokke had constructed a Brachyt of 16 cm aperture by himself; unfortunately, this instrument - later in the Deutsches Museum, Munich, suffers from unrepairable coma.

After four years of sparetime work, and then still unaware of Zschokke's work (which he later rated as an advantage), Kutter had developed an instrument which was obstruction free, and which he called "Neo-Brachyt;" however, this was actually already the modern anastigmatic version of the Schiefspiegler. Tremel started to offer kits to build these instruments. Unfortunately, World War II ended these endeavors, as optical parts became unavailable for the private sector.

After WW II, Kutter completed documentation and published his book, "Der Schiefspiegler," in 1953 (Kutter 1953). In subsequent years, this telescope design became popular, and in the 1960s, Lichtenknecker Optics started to offer Kutter Schiefspiegler mirrors. Both complete instruments and kits for making Schiefspieglers were offered from the Kosmos Verlag company (Kutter 1964). Nowadays, complete instruments of this design are offered e.g. by Astro-Optik Kohler, Switzerland.

In 1975, Anton Kutter proposed a new three-mirror design, the Tri-Schiefspiegler. In the following, other telescope designers entered the field and ceated variants of the Schief with up to four mirrors (Tetra-Schiefspiegler).


Hartmut Frommert [contact]

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