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20 July 2010 The ADC for the VST Telescope: theory and preliminary test of the electromechanical system
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The VST telescope is equipped with an Atmospheric Dispersion Corrector to counterbalance the spectral dispersion introduced by the atmosphere. The well known effect of atmospheric refraction is the bending of incoming light due to variable atmospheric density along the light path. This effect depends on the tangent of the zenith angle and also varies with altitude, humidity and wavelength. Since the magnitude of refraction depends on the wavelength, the resulting effect is not only a deviation of the light beam from its original direction but also a spectral dispersion of the beam. This effect can be corrected by introducing a dispersing element in the instrument. In the VST case the device that compensates for this effect is based on a set of four prisms in two cemented doublet pairs. The system provides an adjustable counter dispersion by counter-rotating the two pairs of prisms. The counter-rotating angle depends on the atmospheric dispersion, which is computed with an atmospheric model using both environmental data (temperature, pressure, humidity) and the telescope position. Two different approaches have been compared for the computations to cross-check the results. The electromechanical system has been assembled, tested and debugged prior to the shipping to Chile. This paper describes the atmospheric models used in the VST case and the most recent phases of work.
© (2010) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Pietro Schipani, Jacopo Farinato, Carmelo Arcidiacono, Sergio D'Orsi, Luigi Ferragina, Davide Fierro, Demetrio Magrin, Laurent Marty, Francesco Perrotta, Roberto Ragazzoni, and Gabriele Umbriaco "The ADC for the VST Telescope: theory and preliminary test of the electromechanical system", Proc. SPIE 7739, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation, 773948 (20 July 2010);

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