The "Brachy" Telescope

[Brachy Telescope] In 1876-77, Vienna opticians Karl Fritsch and J. Forster developed a telescope, of an "excentric Cassegrain" design, which closely resembles the modern Schiefspiegler, which they called "Brachy Telescope." Basically, the primary and secondary mirror of such a telescope are leaned, or inclined. The motivation for this construction was having an unperforated primary mirror; unfortunately, and unlike the modern Schiefspiegler, the Brachy telescope was not obstruction free, as the secondary tube and mirror obstructed some part of the edges of the primary. Forster and Fritsch used spherical mirrors for this construction. See Fritsch (1877), also Common (1895a) and Common (1895b).

In an optical workshop taken over from the Vienna optician Prokesch, Fritsch manufactured Brachy telescopes of 106 (4-inch) and 160 mm (6.3-inch) aperture. In 1880, a 32-cm (12.6-inch) Brachy telescope was delivered to the Pola Naval observatory. While not exactly widespread, Fritsch's Brachy telescopes were still offered in 1912.

The image in this page shows a "Brachyt" by Fritsch as represented in an old book. The caption reads:

Fig. 258. Brachyt nach Fritsch vorm. [vormals] Prokesch.
S1 Objektivspiegel am unteren Ende des weiten, kurzen Rohrs, S2 zweiter Spiegel, O Okular, a Sucher, m Mikroskop zur Ablesung des Deklinationskreises k2, p1 Gegengewicht des Fernrohrs, p2 Übergewicht, u Uhrwerk zur Bewegung um die Stundenachse.

Translation [hf]:

Fig 258. Brachyt after Fritsch, formerly Prokesch.
S1 objective [primary] mirror at the lower end of the wide, short tube, S2 second[ary] mirror, O eyepiece, a finder scope, m microscope for reading the declination circle k2, p1 counter weight of the telescope, p2 overweight, u clockwork for movement around the hour axis.

Anton Kutter, the inventor of the modern Schiefspiegler, stated in 1953 that to his unluck, he had never seen or tested the optical quality of the Brachyt until that time (Kutter 1953).

References:


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