The Renovation of the Bamberg Refractor
Photos: The Bamberg Refractor within the 11m dome of the Wilhelm-Foerster-Observatory on top of the Insulaner.
The main instrument used at public observing sessions at the Wilhelm-Foerster-Observatory is the 107 year old Bamberg refractor. However this is currently being renovated over a period of at least 9 months. The renovation is being conducted by the "4H Jena Engineering" firm. The required funds for this (more than 400.000 DM) were provided by the "Stiftung Deutsche Klassenlotterie Berlin". A cultural and historical exhibition about the instrument has been made by the "ReFIT e.V." society in Jena.
In the meantime the public tours and viewings within the observatory will be done instead with the computer guided 75cm RC reflector, which is the most powerful telescope within Berlin in terms of light collecting. Within the main dome of the Bamberg refractor a replacement refractor (made within the facilities of the planetarium and by members of the WFS) will be installed.
The Bamberg refractor was manufactured in 1889 by the firm Carl Bamberg in Berlin-Friedenau for the then just formed Urania society, co-founded by Wilhelm Foerster. With an aperture of 314mm and a focal length of 5m it was the greatest telescope in Prussia of its time. After WWII the instrument was installed in a facility in the Papestraße, until 1963 it moved to the new observatory building on top of the Insulaner. The observatory is run by the society Wilhelm-Foerster-Sternwarte e.V., which also runs the "Großplanetarium" (large planetarium) in front of the Insulaner.
The total telescope weight, with its mount, is 4.5 (metric) tons, but can easily be moved by hand. Despite its age it was used until the last day before renovation. At public sessions the telescope provides magnifications between 70 and 700x. The 11m dome sometimes hosts hundreds of visitors, who frequently come to the observatory on school trips or at special events like solar or lunar eclipses.
W. Tost (September 1996) see also a brief history of Berlin astronomy