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The VST telescope is going to be commissioned in Paranal, together with its main sub-systems, such as the Image Analysis and Auto-Guiding system. A preliminary work of fine tuning of each sub-system has been performed in Italy before their shipping to Paranal, where they are waiting for the telescope AIV to be completed in a way to start the final commissioning of the overall system. Each unit has been extensively characterized and tested, with particular care to the Active Optics Shack-Hartmann sensor and to the Auto-Guiding arm. We describe here the phases concerning the integration and test of all the VST Auxiliary Units performed in Italy before their shipping to Paranal.

The 2.6-m primary mirror of the VST telescope is equipped with an active optics system in order to correct low-order aberrations, constantly monitoring the optical quality of the image and controlling the relative position and the shape of the optical elements. Periodically an image analyser calculates the deviation of the image from the best quality. VST is equipped with both a Shack-Hartmann in the probe system and a curvature sensor embedded in the OmegaCAM instrument. The telescope control software decomposes the deviation into single optical contributions and calculates the force correction that each active element has to perform to achieve the optimal quality. The set of correction forces, one for each axial actuator, is computed by the telescope central computer and transmitted to the local control unit of the primary mirror system for execution. The most important element of the VST active optics is the primary mirror, with its active support system located within the primary mirror cell structure. The primary mirror support system is composed by an axial and a lateral independent systems and includes an earthquake safety system. The system is described and the results of the qualification test campaign are discussed.