The image quality error budget for the VST telescope

Abstract

VST is a survey telescope with a wide field of view (1°x1°). This makes necessary to investigate the image quality over the whole field of view and not just in the centre. The image quality is studied in terms of diameter enclosing the 80% of the PSF energy. Several error sources are analyzed and optical sensitivity analysis are carried out to know the effect of each individual error source on the image quality. The individual contributions are added quadratically in the assumption they are uncorrelated. The worst case is generally found in the border of the field. The average of the results obtained in a number of fields along the whole field of view is considered as a metric for the telescope optical quality. The overall budget is a continuous work in progress because the requirements for the different subsystems, starting from the initial predictions, are then fed back by test data and further analysis.