The Very Large Telescope Survey Telescope (VST) is equipped with an active optics system in order to correct low-order aberrations. The 2.6 m primary mirror is supported both axially and laterally and is surrounded by several safety devices for earthquake protection. We describe the mirror support system and discuss the results of the qualification test campaign.

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The VIRMOS Consortium has the task to design and manufacture two spectrographs for ESO VLT, VIMOS (Visible Multi-Object Spectrograph) and NIRMOS (Near Infrared Multi-Object Spectrograph). This paper describes how the Mask Manufacturing Unit (MMU), which cuts the slit masks to be used with both instruments, meets the scientific requirements and manages the storage and the insertion of the masks into the instrument. The components and the software of the two main parts of the MMU, the Mask Manufacturing Machine and the Mask Handling System, are illustrated together with the mask material and with the slit properties. Slit positioning is accurate within 15 µm, equivalent to 0.03 ′′ on the sky, while the slit edge roughness has an rms on the order of 0.03 pixels on scales of a slit 5 ′′ long and of 0.01 pixels on the pixel scale (0.205 ′′ ). The MMU has been successfully installed during July/August 2000 at the Paranal Observatory and is now operational for spectroscopic mask cutting, compliant with the requested specifications. Subject headings: instrumentation: spectrographs1

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