Modeling wide-field telescopes in presence of misalignments: an application to the Vera C. Rubin Observatory

An accurate alignment of the optical surfaces of a telescope is essential to guarantee an optimal image quality since even small displacements introduce aberrations increasing towards the edges of the field. This effect is especially detrimental in wide-field imagers. This work proposes the derivation of a fully analytical model of the wavefront error as a function of the most likely system misalignments. An accurate response of the telescope under a predefined set of misaligned conditions is obtained through simulations in Zemax OpticStudio. The resulting data is combined through an integrated modeling approach, obtaining a map of the aberrations as a function of a vector of perturbations applied to the optical system. The analytical wavefront error allows for a quick and accurate assessment of the theoretical PSF across the entire image field. As a case study, the example of the Rubin Observatory is adopted, featuring an 8.4m primary mirror and a large field of view.