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The AO testing facility at the Coudé focus of the Copernico Telescope is now available for on-sky experimentation, a permanent laboratory with the aim of hosting visiting multi-purpose instrumentation that may be directly tested on sky. The Copernico telescope, part of INAF – Astronomical Observatory of Padova, with its 182 cm primary mirror, is the biggest visible telescope in Italy. It is an equatorially mounted classical Cassegrain with equivalent focal number F/9 and offers four focal stations: the Cassegrain focus, two Nasmyth foci and the Coudé focus, which has seen the opening in October 2018.
The 182cm Copernico Telescope at Cima Ekar-Asiago
Coudé Focus Specifications
Coudé Focus Specifications
Testing at the AO facility
Testing at the AO facility
The AO laboratory is now accessible for visiting instrumentation allowing for direct on-sky testing by instrument teams using their own stand-alone instruments and providing a scientific or technical test bench for new instrumental concepts, which may eventually be incorporated later in other instruments. This facility is intended for the implementation of dedicated equipment so optical experimentation can be carried on for relatively short periods of time.
The laboratory at the Coudé Room is enclosed in a light tight room measuring approximately 20 m2. The room can be darkened as needed with dimming lights and is thermally insulated, so optics are kept under stable temperature control. An optical bench of dimensions 2400x1200mm is present, on which users can set up their own instruments.
The AO Laboratory at the Coudé focus
The final transmitted beam at the Coudé focus has the following characteristics: a F/20 aperture ratio with a maximum unvignetted field of view of 2.4 arcmin and a scale of 5.6 arcsec/mm. A folding mirror (F4) redirects the beam parallel to the optical bench with a height of about 15cm between the bench and the optical axis (with the possibility of adjusting it through the insertion of folding mirrors). One of the main characteristics is that of the beam being telecentric, thus giving the system a versatile configuration that allows for a large range of optical set-ups to be arranged for on-sky testing. By analysis based on the system tolerances, the maximum non-telecentricity angle of a star in the field with respect to the optical axis is expected to be <2 arcmin.
The system is currently equipped with an auto-guiding camera that compensates for drifts of the image caused by tracking errors and flexures. A summary of the system specifications is given in the Table.
Optical bench set-up with optical components positions and dimensions, in mm, showing available space for instrumentation.
A sketch of the workbench set-up is shown in the Figure above, together with the optical components in the current configuration. The approximated available space on the workbench for the host instrumentation is shown, taking into account all the mounting components, dimensions are expressed in mm. The Coudé focal plane (FP) is at a distance from F4 of 710mm, with a focal extraction from the last surface of beam splitter (BS) of ~290mm. Precise focusing can also be done, if necessary, by moving the secondary mirror.
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