Vibrations and inaccuracies of the guiding system will have the effect of widening the angular image size obtained by a telescope following the course of a sky object during the required exposure time.
Modern telescopes benefit from the progress in low-friction bearings and electro-mechanic drives. Also the performance of active loop control systems has progressed very close to the theoretical limits. Thus the guiding accuracy of a modern telescope is mainly limited only by the mechanical turbulence of the wind acting on the telescope structure. A first quantification of the perturbation brought by the wind will be given by the portion of the energy density spectrum at frequencies greater than the bandwidth of the guiding loop.