Construction of the FORS focal reducer spectrographs: Status report and first test results

The hardware construction of FORS1, the first of the two focal reducer/low dispersion spectrographs of the ESO Very Large Telescope (VLT), is now finished. An extensive testing programme is under way which will guarantee that the instrument is fully understood and well calibrated when it will be installed at the Cassegrain focus of the first Unit Telescope of the VLT in 1998. This programme includes a full characterization of the optical system and the evaluation of the setting accuracies and reproducibility of the numerous electromechanical functions as well as testing the flexure compensation which will minimize image shift during telescope motions. Telescope and star simulators were specially built for this purpose in order to test the optical and mechanical behaviour of the instrument on the 8m-telescope. Acceptance tests of the optical performance and the subsystem tests of all electromechanical functions indicate an excellent quality, especially for the complex Multi Object Spectroscopy unit, while the overall system tests are just starting.