The 152 cm Cassini telescope

18/08/2018

The 152 cm telescope, inaugurated in September 1976, is dedicated to Gian Domenico Cassini. It is located on Mount Orzale, 500 m from the old 60 cm reflector.
The telescope was designed by the French firm REOSC.
Its structure is very different from that of a classic telescope: there is no tube, and the optics are supported by an iron framework. Counterweights balance the telescope, in order to minimize the stress which could compromise pointing and tracking accuracy. The optical system is formed by a main mirror with a diameter of 152 cm, with a central hole, and by a secondary mirror with a diameter of about 60 cm. The secondary mirror is located in front of the main mirror at a distance of 4m, and reflects the light through the hole, into the observing instruments. REOSC also designed the dome, which was built by Comeva of Vicenza. The Ritchey – Chrétien optical system has a wide (70-arcminute) corrected field. The building was designed by the Technical Office of the University of Bologna, in a joint project with the Astronomy Department, and relying on the experience developed by REOSC in the Haute Provence (France) and ESO (Chile) buildings. It has 3 floors. The ground floor has a 3.5 m ceiling and was designed to host the mirror-alluminizing equipment. On the first floor are an office-living room and the control room of the telescope. The second floor hosts the telescope and has a large lifting platform as a general facility during maintenance and observations. The telescope is supported by two concrete pillars, which have independent foundations and no point of contact with the other parts of the building. This prevents the transmission to the telescope of vibrations produced by the movements of the dome and mobile floor. The main instrument is BFOSC (Bologna Faint Object Spectrograph and Camera), a focal reducer with multi-functional optics.

 

Characteristics

Optical configuration Ritchey-Chrétien
Mount Type English
Total weight 9000 Kg
Main concave mirror total diameter 152.4 cm
useful diameter 150.0 cm
focal ratio F/3
Secondary mirror total diameter 58.0 cm
useful diameter 55.5 cm
Mirror distance 308.7 cm
Cassegrain Focus equivalent focal length 1200 cm
equivalent focal ratio F/8
scale 17″/mm
useful corrected field 70′